Composite Valves

Composite valves are made from strong, light weight composite materials. Their graphite and fiberglass reinforced thermoset and thermoplastic resins are resistant to acids, caustics, bleaches and more than one thousand other industrial and waste treatment chemicals, at half the cost of traditional alloy valves.

Go to Specific Subject: Basics about Composite Valves | Application and Selection of Composite Valves | Typical Composite Valve Specifications | Composite Valve Applications | Other Useful Composite Valves and Materials Links

 

Basics about Composite Valves

Nil-Cor^® Engineering Presentation - Wiliam Simendinger - This comprehensive composite valve seminar whilst being a huge download at over 20 Megs is well worth taking a look at, it covers the Basics about Composites, Composite Processing Methods, Composite Valve Design and Advantages, Composite Valve Applications an more. 

Nil-Cor^® Composites Guide  - Advanced composites are a family of high-performance materials consisting of a polymer matrix reinforced with a fiber. Nil-Cor Operations has pioneered the development of industrial products based on high strength, high stiffness, lightweight glass and graphite fibers in high performance plastic resins since 1966.

 

Application and Selection of Composite Valves

Nil-Cor^®Corrosion Guide - This guide has been developed to assist designers and process engineers in the application and selection of corrosion resistant valves.

Composite Valves can Solve your Internal and External Corrosion Problems - Valves are exposed to corrosive environments both internally (media) and externally (ambient conditions). Since either source of attack can ruin a metal valve or a plastic valve, such as PVC, each deserves serious attention.

 

Typical Composite Valve Specifications

• Typical Composite Control Ball Valve Specification
• Typical Composite Ceramic - Lined Ball Valve Specification
• Typical Composite Butterfly Control Valve Specification

 

Composite Valve Applications

Composite Valves in Wastewater Treatment Plant Applications - William H. Simendinger - Composite valves incorporated into Blue Plains Advanced Wastewater Treatment Plant outperform expectations while helping improve operations.

Butterfly Valve is Corrosion-Resistant Inside and Out - thomasnet.com - The butterfly-valve’s light-weight body is made of corrosion-resistant fiberglass-reinforced cast epoxy. The body, successfully tested to 800 PSI, combines outstanding strength and durability with high-heat resistance in corrosive environments. The valve features an integral ISO 5211 actuator mounting flange for strength and convenience.

Advanced Composite Valves selected for CVN-78 Gerald R Ford Nuclear Aircraft Carrier - Nil-Cor a manufacturer of corrosion resistant, light weight composite valves, will be supplying non-metallic ball valves for the new CVN-78 GERALD R. FORD-class nuclear powered aircraft carriers. This will be the first time that the U.S. Navy has installed non-metallic valves aboard a combatant vessel. Nil-Cor is the world’s largest manufacturer of composite valves, which are not affected by the corrosive nature of seawater and also provide a substantial weight savings.

Composite Pipe Valves Offer Corrosion-Free Performance - Composite valves and actuators have gained entry into offshore facilities, as well. At about one-third the weight of steel, fiber-reinforced composite flow control components are a welcome addition to piping systems and increasingly in demand for marine environments as a high-strength, corrosion-resistant alternative to steel or injection-molded plastics. From Composites World.

 

Other Useful Composite Valves and Materials Links

Development of a Family of Commercial Marine Composite Ball Valves - Vinod Bhasin, Dennis Conroy/NSWC, and Jim Reid/NAVSEA -from sigmatechconsulting.com. 

An Overview of Composite Plastics - from polymerplastics.com.

Facility Piping - Composite piping reduces offshore platform loads, saving cost in system design. From Composites World.

Fiberglass Ideal For Dry Deluge System Applications -  Around 1982, offshore platforms began using dry deluge systems, where the ring main is kept full of seawater but the downstream piping is dry. The dry piping is separated from the ring main by deluge valves, which automatically open and distribute water through the dry pipe to spray nozzles during a fire. This practice saves weight and minimizes corrosion-induced that the deluge piping is typically routed to avoid hazardous areas on the platform means that conductivity is not a requirement, but fire resistance is essential.

Composites World - Composites World is a useful website which is focused on composites.

Seven Things you must know before Selecting Composite Solenoid Valves for your Reverse Osmosis System - Anne-Sophie Kedad-Chambareau,  Roy Bogert, and David Park - This interesting white paper from ASCO highlights some important aspects of composite solenoid valve selection and design.

Understanding the New Lead-Free Water System Regulations - and Choosing Valves to Comply - Anne-Sophie Kedad-Chambareau - In the U.S., regulations governing lead content of the components of potable water systems have seen considerable changes as safety restrictions tighten. The federal law in effect since January 2014 dictates much lower lead content for certain systems and components than in the past. Manufacturers of potable water equipment and systems - including drinking water fountains, R/O (reverse osmosis) systems, coffee machines, and commercial kitchen equipment - as well as equipment maintenance contractors are affected. Many remain uncertain how the new regulations will impact their manufacturing and purchasing. This report outlines relevant sections of the law. It then focuses on the choices facing specifiers and purchasers who need to select important components of these systems - two-way solenoid valves - to comply. It considers the calculations that must be made to determine average lead content. Finally, it discusses the pros and cons of common valve materials (brass, composite/plastic, stainless steel, and lead-free brass), as well as other selection advantages. Original equipment manufacturers (OEMs) and contractors will get useful information to ensure their equipment remains efficient, safe, and compliant - from ASCO.

Control Valve Actuators

Go to Specific Subject: Compact Valve Actuator Solutions and Systems | Subsea Valve Actuators | Offshore Valve Actuator | High Pressure Manifolds Actuators | Safety Related Systems Valve Actuator Systems | Spring Return Hydraulic Actuators | Spring Return Pneumatic Actuators | Compact Double Block & Bleed (DBB) Valve Actuators | Double Acting Actuator | Compact Actuators in Floating Liquefied Natural Gas (FLNG) Applications | Valve Actuator General Information | Scotch Yoke Design Valve Actuators | Firesafe Actuators | Valve Actuator Standards | Hydraulic Actuator Design and Operation | Electrical Actuator Design and Operation | Control Valve Actuator Design and Operation | Valve Actuator Accessories

 

Control / On - Off Valve Actuator Description

Control, On-Off Ball, Gate, Globe and Butterfly valves all require a mechanism to actually “drive” them, this is what is called an “Valve Actuator”. These Valve Actuators come in various forms, and use various power sources as an operating medium. Typically the power sources utilised by the Instrument and Control System design engineers is pneumatic, hydraulic and electrical. Of course the most basic actuator is a manual hand wheel.

Design of the Valve Actuator - The design engineer has to consider the operating conditions such as:

1. The atmosphere and potential corrosion. If the Actuator is being utilised on an Offshore Platform or FPSO then particular care must be taken in selecting the actuator body materials and internal mechanism. Particular emphasis on this should be taken on the tubing associated with pneumatic actuators or any that ‘breathe’ on the return stroke, potentially sucking in salt or corrosive air into the internal mechanism. Under this scenario a technique called closed loop breathing is used (an excellent schematic of a typical system can be found here). Selection of any accessories such as quick exhaust, solenoid valves and limit switches etc must also consider the conditions. In the Offshore Oil and Gas Industry 316SS Actuators are sometimes selected.
2. Torque requirements must be carefully considered as too little power can mean that any stiction in the valve means that the valve may stick in the cycle. Too much power may actually cause the valve mechanism to shear.
3. Pneumatic Valve actuator 0 - 100% cycle may be various pressures, control valve actuators are generally 3 - 15 psi (20 - 100kpa). However they may sometimes be set differently to this.
4. On - Off Valve Actuators may be set to other pressures, commonly 0 to 100 psi, this is to keep the size of actuator as compact as possible.
5. Hydraulic Valve Actuators utilise much higher pressures, especially on very large ball valves, this design is used to obtain the higher torques required and to keep the actuator and valve footprint as compact as possible.
6. Smart Positioners may be used both on Control and On - Off Actuator Valve combinations, these are a superb maintenance tool in that the Valve/Actuator signature at new conditions can be taken. Any changes outside parameters then mean that any maintenance is condition based.

 

ATC Valve Actuators Technical Information, White Papers and Application Details

ACT Actuators accommodate a specific market need for a compact spring return actuator to operate quarter turn and linear operated valves. Applications that particularly benefit from their compact design are those where installation space is limited, like on topsides, high-pressure manifolds, internal / external turret areas and (vertical mounted) riser valves. A compact actuator design could also benefit the handling, mounting and alignment in case large valve sizes/high pressure ratings do apply. Due to the enhanced actuator design, ATC actuators are also installed in shallow to ultra deepwater, and available complete with ROV interfacing and receptacles to ISO. ATC actuators are SIL 3 compliant to IEC 61508 and are manufactured in compliance with the ISO 9001 2000 quality procedures.

 

Compact Valve Actuator Solutions and Systems

Compact Actuator Solutions and Systems - Some comprehensive Compact Actuator Design Information and Application details from Prochem.

 

Engineering Features of the ATC Valve Actuator

• Compactness - Design flexibility, combined with the innovative integration of all actuator parts, results in the most compact actuator available in the market. In virtually all applications, irrespective of hydraulic or pneumatic supply, the ATC actuator diameter is smaller than the Face-to-Face dimension of the valve. The ATC actuator enables designers to minimize overall dimensions, reduce platform weight & deck load and ease the design of steel support structures.
• Enhanced Performance - ATC compact actuators are based on an advanced compact design with a revolutionary self-lubricating, low-friction torque conversion mechanism which eliminates the risk of any mechanical wear and tear. If the application requires an advanced level of optimization (in dimensionsor torque), the actuator output can be adapted to the exact valve torque.As a further benefit, the air or oil displacement can be reduced by up to 50%, contributing to savings in the control system, HPU or airset.
• Reliability - Due to its innovative yet simple design, the ATC compact actuator is based on a minimum number of parts. As a result, maximum reliability is ensured throughout our entire range. ATC compact actuators are hermetically sealed, airtight and watertight under all conditions. A complete FMECA has been carried out, including verification of the complete global installed base. As a result, TUV Rheinland has certified the ATC actuators to SIL 3, in accordance with IEC 61508, and field-proven Type A. In addition the ATC actuator has been tested extensively in accordance with the Shell type approval test procedure (DEP 31.40.70.30) and the API 6A PR2 procedure. These tests included extensive functional and seal testing, a compressed spring test and a dynamic load cycle test at 95% of the maximum torque for a total of 6200 cycles at temperatures ranging from minus 20C to 65C. The successful completion of these tests has been certified by an independent body.
• Cost Savings for Contractors and Operators - Contractors can benefit directly from using ATC compact actuators, both at the FEED stage and the EPC(I) stage. The number of engineering hours (e.g. for piping lay-out) has been reduced drastically on a considerable number of projects. ATC compact actuators also make it possible to cut material costs and weight thanks to an optimised and shortened piping lay-out. In addition due to the nature of the design, no specific maintenance programs are required on ATC actuators during the lifespan of your project. Consequently, ATC compact actuators result in maximum availability at lowest operational cost without requiring periodic maintenance - not even actuator replacement!

 

Subsea Valve Actuators

Subsea Actuator Technical Features - ATC has a complete line of sub-sea actuators available suitable for shallow water applications and installation in ultra deep waters, including ROV interfacing. This includes Submerged production, Submerged (off) loading, Sub Surface Isolation Valve (SSIV), PLEMS, Subsea Manifolds, Production Valves, Pipeline Valves, and Pigging Valves.

Subsea Quarter Turn

Subsea Linear

 

Offshore Valve Actuator

Topside Actuator Applications - Topsides / Manifolds, FPSO Turrets, Loading Buoys, Riser Valves, Isolation Valves, and Ballast Valves.

Upstream Quarter Turn Hydraulic

Upstream Quarter Turn Pneumatic

 

High Pressure Manifolds Actuators

Application of Compact Actuators on High Pressure Manifolds - Space and Weight are an important consideration when designing Valving and their associated actuators on High Pressure Manifold Systems. Actuators which can be installed in different angles provide significant advantages. By utilizing Compact Actuators a “minimum design footprint” can be achieved.

 

Safety Related Systems Valve Actuator Systems

Actuator for Safety Related Systems - The ATC spring return actuator offers an enhanced reliability, while having a minimum quantity of actuator parts. A complete FMECA has been carried out in conjunction with a complete review of our installed base. The actuator is certified by TUV Rheinland to meet SIL 3, following IEC 61508 and based on a 1oo1 architecture applied.

Applications - Overpressure Protection Systems, HIPPS, and ESDV.

 

Spring Return Hydraulic Actuators

Spring Return Hydraulic Actuator Technical Features - The standard ATC spring return actuator is the most compact actuator available in the market. In short, the ATC actuator offers the following advantages:

 

Spring Return Pneumatic Actuators

Spring Return Pneumatic Actuators Technical Features - Due to the innovative design, The ATC pneumatic spring return actuator is available in dimensions which are close to the hydraulic version and therefore uniquely compact.

 

Compact Double Block & Bleed (DBB) Valve Actuators

Compact Double Block & Bleed (DBB) Valve Actuator Technical Features - The ultra compact ATC actuator allows for “redundant actuation” within one valve body (DBB) rather than using 2 individually installed valves. This optimisation results in a considerable reduction in pipe length, flanges, adapter sets and having the most impact in case exotic pipe materials are applied.

 

Double Acting Actuator

Double Acting Actuator Technical Features - The ATC double acting actuator is based on the same unique design approach and flexibility as applies to the spring return range.

 

Compact Actuators in Floating Liquefied Natural Gas (FLNG) Applications

FNLG Vessel Design Requires the Latest Weight and Space saving Concepts - Space and weight saving on FLNG facilities are an essential design parameter as “real estate” is very limited. Hence Compact Actuators are an important component in achieving this design goal and have been utilised in major projects around the world. Also whilst space and weight are paramount the additional savings associated with Passive Fire Protection add to the overall justification and use of these products.

 

Valve Actuator General Information

Valve Actuator - Actuators are used for the automation of industrial valves and can be found in all kinds of technical process plants: they are used in waste water treatment plants, power plants and even refineries. This is where they play a major part in automating process control. The valves to be automated vary both in design and dimension. The diameters of the valves range from a few inches to a few meters. Depending on their type of supply, the actuators may be classified as pneumatic, hydraulic, or electric actuators - This link from Wikipedia gives lots of technical information.

General notes for the Calculation and Selection of Actuators - These general notes from Samson Controls are useful.

A Descriptive Definition of Valve Actuators - Chris Warnett - A valve actuator is any device that utilises a source of power to operate a valve. This source of power can be a human being working a manual gearbox to open or close a valve, or it can be a smart electronic device with sophisticated control and measuring devices. With the advent of micro-circuitry the trend has been for actuators to become more sophisticated. Early valve actuators were no more than a geared motor with position sensing switches. Today’s valve actuators have much more advanced capabilities. They not only act as devices for opening and closing valves, but can also check on the health and well being of a valve as well as provide predictive maintenance data - from Rotork Controls Inc and Valve World.

 

Scotch Yoke Design Valve Actuators

Scotch Yoke - The Scotch Yoke principle is characteristic for its high torque when required - at the beginning and end of each operation. This increases safety, especially in applications where the valve remains stationary throughout long periods. From Austral Powerflo Solutions and Remote Control.

Scotch Yoke or Rack-and-Pinion Pneumatic Part-turn Actuator? - Günter Öxler - This article reports on the best choice between the different technical solutions offered by pneumatic part-turn actuators - from Valve World.

 

Firesafe Actuators

Firesafe Actuators - Thanks to Samson Controls.

 

Valve Actuator Standards

EN 15714-1:2009 - Industrial valves - Actuators - Part 1: Terminology and definitions.
EN 15714-2:2009 - Industrial valves - Actuators - Part 2: Electric actuators for industrial valves - Basic requirements.
EN 15714-3:2009 - Industrial valves - Actuators - Part 3: Pneumatic part-turn actuators for industrial valves - Basic requirements.
EN 15714-4:2009 - Industrial valves - Actuators - Part 4: Hydraulic part-turn actuators for industrial valves - Basic requirements.

 

Hydraulic Actuator Design and Operation

Hydraulic Actuator Design and Operation - Pneumatic actuators are normally used to control processes requiring quick and accurate response, as they do not require a large amount of motive force. However when a large amount of force is required to operate a valve hydraulic actuators are normally used - from Engineers Edge.

 

Electrical Actuator Design and Operation

Control Valve Actuators - Their Impact on Control and Variability - Chris Warnett - Electric control valve actuators provide excellent performance and are ideal for oil and gas wells in remote production fields. Instrument air supply systems are costly and require significant energy to run. If mains power isn’t available, an instrument air supply isn’t practical, especially when only a few control valves are in use at a location. Solar powered DC electric actuators are ideal for such an application - from Rotork.

How Electric Control Valve Actuators Can Eliminate The Problems of Compressed Air as a Power Medium - Today, a new major technological advance is available that can help control-valve users avoid many of the problems and inefficiencies associated with using compressed air as a power medium. The new solution uses electric power and eliminates dependence on compressed air. This totally electric solution is appropriate and cost-effective for a wide variety of control-valve applications, including those found in such sectors as power generation, chemical, petrochemical, and most other process industries. While the new generation of electric control-valve actuators may not be suitable for all process applications, it is ideal for many situations, especially where users have experienced problems with frozen air hoses, lack of process precision, stick slip, and so on. Therefore, it is prudent for today’s process control engineers to take a serious look at how the design features of the new generation of totally electric control-valve actuators can benefit them - from Rotork.

Specification - Electric Valve Actuators in Water and Wastewater Treatment Plants - This is a typical specification from Auma Actuators, whilst product specific it is a useful basis for developing a specification.

Guidelines for the Specification of Electric Valve Actuators - This draft standard provides general requirements for the development of specifications for electric actuators - from the ISA.

General Specification for Electric Actuators - Integral Motor Control - This is a typical specification from Rotork Actuators, whilst product specific it is a useful basis for developing a specification.

 

Control Valve Actuator Design and Operation

The Fisher Control Valve Handbook - This superb 295-page PDF whitepaper is a control valve resource that has been consistently updated for 30 years. It contains vital information on control valve performance and latest technologies. Thanks to Emerson Process Management.

Control Valve Actuator Bench Set Requirements - Jerry Butz - Control Valve “Bench Set” is an often-misunderstood point of confusion, and sometimes incorrectly described part of a control valve’s actuator specifications. But not understanding it can set one up for a failure in the form of a mis-sized actuator and spring. Maybe this information can help to clear the cloud of confusion and make it easier for engineers, technicians, and operators to understand - from Flow Control.

Understanding Control Valve Bench Set - Dave Harrold-from Control Engineering.

Control Valve Actuators and Positioners - Control valves need actuators to operate. This tutorial briefly discusses the differences between electric and pneumatic actuators, the relationship between direct acting and reverse acting terminology, and how this affects a valve's controlling influence. The importance of positioners is discussed with regard to what they do and why they are required for many applications - from Spirax Sarco.

Control Valve Actuator Options - Today’s Actuators Offer Imposed Performance With Lower Life-Cycle Costs. The Challenge Is Choosing the Right One for the Application - George Ritz - Over the past several years, valve actuators have received relatively little attention while process control specialists concentrated on controllers, sensors, and other components of the control loop. This is borne out by the unglamorous nickname “pig iron” assigned to the actuator/control valve unit. With the onset of the smart-valve generation, it suddenly appears that the control valve actuator may get more respect along with its new electronics degree - from CCI.

Linear Pistion Actuators - Samy, Stemler - High Reliability of actuation is of paramount importance in the nuclear power industry. Pneumatic actuators form the largest installed base with many in safety significant applications. This paper addresses the issues related to actuation, such as available Thrust, Stiffness, Sensitivity, Hysteresis, Dead band, Dynamic Stability and a sizing example. This paper also presents comparisons between various types of linear actuators and their relative advantages and disadvantages. Also presented will be evaluation techniques for troubleshooting actuator problems and improving plant performance - from CCI.

Closed Loop Breathing - This is a technique to ensure that corrosive or saline air cannot enter the internals of the valve on the breathing side of the valve. It is very popular in the Offshore Oil and Gas Industry and on Coastal Refineries etc - thanks to Rotork for this excellent schematic.

How to Select an Actuator - Wayne Ulanski - As the process industry continues to achieve more efficient and productive plant design, plant engineers and technicians are faced, almost daily, with new equipment designs and applications. One product, a valve actuator, may be described by some as simply a black box, having an input (power supply or signal), an output (torque), and a mechanism or circuitry to operate a valve. Those who select control valves will quickly see that a variety of valve actuators are available to meet most individual or plant wide valve automation requirements. In order to make the best technical and economical choice, an engineer must know the factors that are most important for the selection of actuators for plant wide valve automation. Where the quality of a valve depends on the mechanical design, the metallurgy, and the machining, its performance in the control loop is often dictated by the actuator - from SVF Flow Controls, Inc.

Control Valve Actuators: Their Impact on Control and Variability - Chris Warnett, In a process plant, the general function of a control valve is to restrict the opening of the valve so it affects the flow or pressure of the liquid or gas that is passing through it. In any given application, an installed valve, whether it is a rotary or sliding stem valve, has one fundamental variable - the position of the moving element. That single moving element determines the exposed orifice that allows greater or lesser flow through the valve, which in turn provides the control of the process. The valve itself may be extremely sophisticated with exotic body and seat material, or it may have complex flow patterns that allow for a high pressure drop or some other function. However, the fundamental requirement to move the valve stem to position the control element remains the same regardless of whether it is a simple or a sophisticated valve. A control valve actuator is used to move the valve stem (which is attached to the internal control element) to the desired position and hold it in place. In addition to the act of moving and holding positions, there are many other parameters to that movement which determine the best type of actuator that should be used for every specific application. For example, other important considerations might include speed, repeatability, resolution, and stiffness - from Rotork Process Controls and Valve World.

 

Valve Actuator Accessories

The following links are provided thanks to Austral Powerflo Solutions.

Rotary Limit Switch Boxes - Rotary limit switch boxes provide a visual and remote electrical indication of quarter turn valve/actuator position (ball, butterfly and plug).

Bolt Switches - "Bolt" switches are magnetic proximity switch suitable for any type of position indication.

Valve Position Indicators - The 3D Series namur indicators provide high visibility verification of valve/actuator position. The indicator features a rotor with red and green quadrants that rotate to indicate valve open and valve closed positions.

Control Valves

This Comprehensive Control Valve Technical Information Page covers Selection and Design, Cavitation and Flashing in Control Valves, Control Valve Actuators, Butterfly Control Valves, Control Valve Sizing, Split Range Control Valves, Control Valve Applications, Control Valve Noise Calculation and Prediction, Control Valve Maintenance, Control Valve Positioners and Self Operated Regulators.

Scroll Down for Technical Information on Control Valves

Go to Specific Subject: Control Valve Selection and Design | Control Valve Handbooks and Design Guidelines | Cavitation and Flashing in Control Valves | Control Valve Characteristics | Control Valve Emission Control | Control Valve Fail Safe Position | Control Valve Leak Class | Control Valve Noise Calculation and Prediction | Control Valve Performance | Control Valve Rangeability | Control Valve Sizing | Control Valve Styles | Control Valve Trim Materials | Control Valve Material Selection, Corrosion and NACE Applications | Control Valve Maintenance | Control Valve for Safety Instrumented Systems Applications | Split Range Control Valves | Control Valve Actuators | Butterfly Control Valves | Control Valve Applications | Control Valve Positioners and Accessories | Control Valve Education | Self Operated Regulators | Emergency Shutdown and Blowdown Valves | Composite Valves | Specialist Power Plant Valves | HVAC Control Valves

 

Control Valve Selection and Design

The following information is from Powerflo Solutions Pty Ltd and Masoneilan.

Selecting a Control Valve - Fluid velocity in a control valve is a key parameter that must be considered when sizing and selecting a control valve. High fluid velocities can lead to erosion damage, trim wear, trim component failure, vibration and high noise levels. Therefore, it is vital to design for valve velocities within acceptable limits so that these problems are avoided. This paper addresses these issues.

Looking Inside the Valve - Asher Glaun - Modern control valves can monitor pressure and flow control in a full range of specialist process industries. Now, even better prediction of a valve's performance can be calculated and it is possible to find out what is really going on inside a valve.

Fluid Velocity Considerations - by Jospeh Shahda, Senior Applications Engineer, Masoneilan Operations.

Why most Control Valves today are Throttling at around 60% opening.

 

Control Valve Handbooks and Design Guidelines

Control Valve Sizing Handbook - This handbook on control valve sizing is based on the use of nomenclature and sizing equations from ANSI/ISA Standard S75.01.01 and IEC Standard 60534-2-1. Additional explanations and supportive information are provided beyond the content of the standards. This document contains information on Flow Coefficient CV, Operating Conditions, Specific Gravity, Pressure Drop across the Valve, Flowing Quantity, Liquid Flow Equations, Liquid Pressure Recovery Factor, Combined Liquid Pressure Recovery Factor, Cavitation in Control Valves, Effect of Pipe Reducers, Equations for Non-turbulent Flow, Gas and Vapor Flow Equations, Multistage Valve Gas and Vapor Flow Equations, Ratio of Specific Heats Factor, Expansion Factor, Two-Phase Flow Equations , Choked Flow. Supercritical Fluids, Compressibility and Thermodynamic Critical Constants - From Powerflo Solutions Pty Ltd, Masoneilan and Instrumentation and Control Net.

Top 10 Masoneilan Control Valve Sizing Handbook Documents for the Instrumentation Technician - from Instrumentation and Control Net.

The Fisher Control Valve Handbook - This superb 295-page PDF whitepaper is a control valve resource that has been consistently updated for 30 years. It contains vital information on control valve performance and latest technologies. Thanks to Emerson Process Management.

Practical Control Valve Sizing, Selection and Maintenance - Dave Macdonald BSc(Eng) - This manual is intended to provide an understanding of the key issues involved in the selection of control valves for typical process industry applications. This chapter looks at the fundamental principles involved in the control of fluid flow and it describes how the adjustment of flow capacity is typically used to control pressure, flow, level and temperature in processes - thanks to IDC.

Control Valve Selection and Sizing Engineering Design Guideline - There are many available guidelines developed to aid engineers in selecting and sizing the valves, but mostly these guidelines are developed by certain companies and might only be suitable for the application of the valves provided by their own companies. Hence, it is important to get the general understanding about control valve sizing and selection first. Later, whenever changes are needed in a process system, this basic knowledge is still applicable. This guideline is made to provide that fundamental knowledge and a step by step guideline; which is applicable to properly select and size control valves in a correct manner. Control valve supports the other devices and work together resulting and ideal process condition. Hence, it is crucial to make some considerations before deciding the correct control valve sizing and selection. The selected valve has to be reasonable in cost, require minimum maintenance, use less energy, and be compatible with the control loop. Malfunction in control valve might cause process system does not work properly - from kolmetz.com.

Ease Control Valve Selection - Trevor Bishop, Meredith Chapeaux, Liyakat Jaffer, Kiran Nair and Sheetal Patel - With so many types and options available, choosing the right control valve can seem daunting. Selection can be simplified by considering the process fluid, the service requirements, and how the various valves function - from CEP Magazine.

Valve Sizing & Selection Technical Reference - This is an excellent resource! -A Control Valve performs a special task, controlling the flow of fluids so a process variable such as fluid pressure, fluid level or temperature can be controlled. In addition to controlling the flow, a control valve may be used to shut off flow. A control valve may be defined as a valve with a powered actuator that responds to an external signal. The signal usually comes from a controller. The controller and valve together form a basic control loop. The control valve is seldom full open or closed but in an intermediate position controlling the flow of fluid through the valve. In this dynamic service condition, the valve must withstand the erosive effects of the flowing fluid while maintaining an accurate position to maintain the process variable. A Control Valve will perform these tasks satisfactorily if it is sized correctly for the flowing and shut-off conditions. The valve sizing process determines the required CV, the required FL, Flow Velocities, Flow Noise and the appropriate Actuator Size - from Warren Controls.

Commonly Asked Questions about Control Valves - This list of questions will be very useful to Graduate Instrument Engineers - from Mitech.

Fluid Kinetic Energy as a Selection Criteria for Control Valves - by Herbert L. Miller and Laurence R. Stratton - Reproduced with the permission of CCI Sulzer Valves.

Your Best Bet in Control Valves - Hans Bauman - Control valves may be the most important, but sometimes the most neglected, part of a control loop. The reason is usually the instrument engineer’s unfamiliarity with the facets, terminologies, and areas of engineering disciplines, such as fluid mechanics, metallurgy, noise control, and piping and vessel design that can be involved depending on the severity of service conditions - From ISA and InTech.

Plant Design and Control Valve Selection under Increasing Cost and Time Pressure, Part 1 - Holger Siemers - Following a career spanning three decades, Mr Siemers is well aware of the pitfalls to be avoided when specifying control valves for a range of demanding applications. In his latest paper for Valve World, he looks further into plant design and control valve selection when working under increased time and cost pressure. This article is split into two parts: broadly speaking, part one looks at control valve operating points and provides a case history involving a mismatch. The author then introduces better valve sizing practices and uses this theory to resolve the problems introduced in the case history - from Conval and Valve World.

Plant Design and Control Valve Selection under Increasing Cost and Time Pressure, Part 2 - Holger Siemers - Part two starts by explaining the trends and definitions of inherent valve characteristics before focusing on "quick and dirty“ sizing. The paper then addresses cavitation before concluding with the expert software available to help select the optimum valve characteristic form - from Conval and Valve World.

The Plant Maintenance Resource Center has some very useful links on Control Valves including;

• Control Valve Concepts - Control Valves Do What They Are Told!
• Control Valve Terminology - A comprehensive terminology list
• Control Valve Tips & Tricks - An excellent list of useful tips and tricks for the control valve user
• Control Valves - Flow Recovery Coefficient
• Control Valves - Pressure Recovery Factor

 

Cavitation and Flashing in Control Valves

Control Valve Cavitation, Damage Control - James A. Stares - This paper outlines the application methods used by leading control valve manufacturers to avoid the damaging effect of cavitation on control valve performance and reliability - from Masoneilan.

Cavitation Guide for Control Valves - J. Paul Tullis - This guide teaches the basic fundamentals of cavitation to provide the reader with an understanding of what causes cavitation, when it occurs, and the potential problems cavitation can cause to a valve and piping system. The document provides guidelines for understanding how to reduce the cavitation and/or select control valves for a cavitating system. The guide provides a method for predicting the cavitation intensity of control valves, and how the effect of cavitation on a system will vary with valve type, valve function, valve size, operating pressure, duration of operation and details of the piping installation. The guide defines six cavitation, limits identifying cavitation intensities ranging from inception to the maximum intensity possible. The intensity of the cavitation at each limit is described, including a brief discussion of how each level of cavitation influences the valve and system. Examples are included to demonstrate how to apply the method, including making both size and pressure scale effects corrections. Methods of controlling cavitation are discussed providing information on various techniques which can be used to design a new system or modify an existing one so it can operate at a desired level of cavitation - from the Office of Scientific and Technical Information.

Control Valve Shutoff Classification and Allowable Leakage Rates - Jerry Butz - Sometimes when commissioning or troubleshooting automatic control valves, it is discovered that the control valve, even though fully closed, doesn’t fully shut off the flow of process fluid through the plug and seat. Although closed, there is an “allowable leakage rate” as part of each control valve’s specification. This article aims to clear up some confusion about control valve shutoff - from Flow Control.

Liquid Flow in Control Valves - Choked flow, Cavitation and Flashing - Jon Monsen - This blog gives details on Choked flow, Cavitation, Flashing and how to prevent Cavitation and Cavitation damage - from Valim.

Cavitation in Valves - Cavitation can occur in valves when used in throttling or modulating service. Cavitation is the sudden vaporization and condensation of a liquid downstream of the valve due to localized low pressure zones. When flow passes through a throttled valve, a localized low pressure zone forms immediately downstream of the valve. If the localized pressure falls below the vapor pressure of the fluid, the liquid vaporizes (boils) and forms a vapor pocket. As the vapor bubbles flow downstream, the pressure recovers, and the bubbles violently implode causing a popping or rumbling sound similar to tumbling rocks in a pipe. The sound of cavitation in a pipeline is unmistakable. The condensation of the bubbles not only produces a ringing sound, but also creates localized stresses in the pipe walls and valve body that can cause severe pitting - from Valmatic.

Video - What's Cavitation in Control Valves? - from Fisher.

Video - Fundamentals of Cavitation and Flashing Video - An explanation of cavitation, how it differs from flashing, the damage that it can cause, and methods of controlling it - from Fisher.

The following links are from Samson Controls:

Cavitation in Control Valves - Cavitation can arise in hydrodynamic flows when the pressure drops. This effect is regarded to be a destructive phenomenon for the most part. In addition to pump rotors, control valves are particularly exposed to this problem since the static pressure at the vena contracta even at moderate operating conditions can reach levels sufficient for cavitation to start occurring in liquids. The consequences for a control valve as well as for the entire control process vary and are often destructive causing: Loud noise, Strong vibrations in the affected sections of the plant, Choked flow caused by vapour formation, Change of fluid properties, Erosion of valve components, Destruction of the control valve and Plant shutdown.

Cavitation - Of the greatest importance in connection with valves has to be “cavitation”. Cavitation develops if liquids - due to high velocity - evaporate temporarily in the interior of the valve. The bubbles filled with vapor proceed through the liquid flow in the direction of the valve outlet. Due to an inevitable pressure recovery behind the throttling area the bubbles reach a zone of higher pressure and this leads to a sudden implosion of these bubbles. The implosion effect forms micro jets with velocities of up to 500 m/s. During the impact of such micro jets on a firm body (e.g. valve body wall or trim), extremely high local pressure peaks occur which can destroy almost any material very quickly.

Control Valves for Critical Applications - Know the Causes of Cavitation and Flashing and How to Prevent Them - J. Kiesbauer - In refineries, the process media flowing through valves are primarily liquids. With liquids, critical operating conditions caused by cavitation or flashing may occur. Symptoms are, for instance, increased noise emission, valve and pipe component erosion or low-frequency mechanical vibration in the valve and the connected pipeline. Under these conditions, in particular, neglecting details can result in negative influences on plant performance and costs of ownership. Unfortunately, common practice today is to select control valves in a “quick and dirty” fashion, because the phases of planning, bidding and order processing are connected with significant pressures of cost and time. This article presents the basic principles underlying these problems and shows how to eliminate them based on practical examples from refineries. Moreover, a new throttling element is introduced, that is especially suited to reducing noise emission produced by cavitation. This new throttling element is being implemented in refineries with increasing success.

Taking the Mystery out of Cavitation Pilot-Operated Automatic Control Valves - Brad Clarke and Kari Oksanen - Cavitation can be an extremely damaging force as related to the application of pilot-operated automatic control valves. The consequences of cavitation are numerous and can include: loud noise, extreme vibrations, choked flow, destruction or erosion of control valves and their components resulting in disruption of water distribution or plant shutdown. This white paper deals with cavitation solutions as they relate to valves and specifically pilot-operated automatic control valves. A high level description of what causes cavitation and the associated impacts is covered. Typical occurrences of cavitation and consequences are also discussed in some detail - from Singer Valve.

Vibration of Valves and Piping - What Would Cause Vibration in a Gas Service, and What Protection Can Be Applied If It Occurs? - A question and answer article from Control Global.

 

Control Valve Characteristics

Guidelines for Selecting the Proper Valve Characteristic - “The tank is overflowing!” Not a nice thought, but that could be a result of a system out of control due to a poor choice of the valve characteristic. Selecting the proper valve characteristic is the easiest way to ensure process stability at all loads. So what valve characteristic to use? This article makes recommendations for the four basic process controlling variables: liquid level, pressure, flow, and temperature. These recommendations are based on a complete dynamic analysis of the process and serve as “rules of thumb” to be used as part of valve selection. The “valve characteristic” refers to the relationship between the position of its flow-controlling element (e.g. valve plug) and its resulting flow. Graphically, this is normally plotted with the valve’s resulting flow on the vertical axis vs. the valve plug’s travel on the horizontal axis. The shape of the resulting output vs. input curve describes the type of valve characteristic - from Emerson Process Management.

Best Control Valve Flow Characteristic Tips - Greg McMillan - Often arguments as to whether a linear or equal percentage trim is best are based on the theoretical inherent flow characteristics. Valve rangeability is often stated as simply a deviation of the catalogue flow characteristic from the theoretical characteristic. Here we will see how the consideration of the changes in process dynamics, available valve pressure drop, and control valve dynamics can alter what you consider as the best flow characteristic - from Control Global.

Control Valve - What you need to Learn? - An interesting paper on Control Valves which includes information on Characteristics, Capacity Sizing and Rangeability - From the School of Chemical Engineering Malaysia.

Determine the Characteristic Curve of an Installed Control Valve - Jeff Sines - The performance of a control valve is defined by its inherent and installed characteristic curves. The inherent characteristic curve is a plot of the percent of valve opening vs. the percent of maximum flow coefficient (CV). The inherent characteristic curve is determined by measuring the flow rate at various positions of valve travel with a fixed differential pressure across the valve (typically 1 psid) and calculating the CV at each position using a form of the generalized Control Valve CV equation - From Engineered Software.

Control Valve Flow Characteristics - Trim design will affect how the valve capacity changes as the valve moves through its complete travel. Because of the variation in trim design, many valves are not linear in nature. The relationship between valve capacity and valve travel is known as the flow characteristic of the valve. Valve trims are specially designed, or characterized, in order to meet the large variety of control application needs. This is necessary because most control loops have some inherent nonlinearities, which you can compensate for when selecting control valve trim - from The Plant Maintenance Resource Center.

 

Control Valve Emission Control

How Stem Finish Affects Friction and Fugitive Emissions with Graphite Based Control Valve Packing - Mark Richardson - In previous papers we have discussed how graphite based valve stem packing can be used in control valve applications. Benefits of using a graphite based packing include improved thermal stability, compared to traditional PTFE chevron seals though, there is a minor penalty of increased friction. However, whilst the PTFE seals have been widely used for many years, achieving reliable performance with graphite packing sets in high cycle duties requires a different approach to the boundary tribology between the packing and stem. Further research into the effect this has on sealing performance and friction characteristics was required, as these were not well documented nor the effects well understood. The optimisation of the stem condition is required in order to achieve a desired high level of tightness, whilst minimising friction. A greater understanding of these factors, specifically in relation to control valve packing, would allow specification of a valve stem finish based on the sealing material and required performance. This paper discusses the equipment, test methods and results generated using the James Walker methane test facility that simulates a rising stem valve. Tests will be carried out on test stems with surface finishes ranging from polished chrome to a rough ground 2.6µm Ra. Effects of increased packing load and thermal cycling on leakage and friction will be investigated including the hypothesis that there is an optimum surface finish specific to a packing, which maximises performance of these two parameters - from James Walker.

The Development of Effective Fugitive Emissions Control for Valves - Dave Cornelsen - This article discusses development and testing work carried out to help reduce fugitive emissions of VOCs through valves. As restrictions tightened, the scope of the programme was widened to include the development of a new stem packing design. This packing was subsequently evaluated in the laboratory and during field trials - from ValveWorld.

Metal Bellows Seal - Stem sealing constructions utilizing a metal bellows seal, guarantee, unlike conventional stuffing boxes, a maintenance-free service and the retention of the specified tightness. However to ensure a life time of approx. 200,000 full stroke cycles - which corresponds normally to a non-interrupted service of several years - most control valves have to be improved in important details. As a rule of thumb, the length of a bellows seal should be approximately ten times the nominal stroke of the control valve. Only such a design ensures an adequate service life - from Samson Controls.

Packing and Gaskets - The chemical industry has carried environmental surveys for many years. These surveys provide valuable information regarding environmental pollution which is usually related to leaking packings and gaskets. Packings are, in principle, gaskets too, they are, however, in addition exposed to dynamic strain. For the reliability of packings or gaskets there are primarily two factors, Suitable selection of type and material, and regular maintenance, in order to avoid wear and tear and a compression of the sealing element - from Samson Controls.

Fugitive Emissions Philosophies for Control Valves - Holger Siemers - It is interesting to compare the use of the bellows seal design versus low emission packing material. The bellows seal design seems to have been forgotten in international discussions and published papers, but it is still unbeatable as regards its life cycle and 'quality of tightness'. In the 'world of valves' under the requirements of fugitive emissions approximately 5% are control valves - thanks to SA Instrumentation and Control.

Fugitive Emissions and Control Valves - This paper describes the history of the development of the fugitive emissions requests, the standards committees and manufactures reactions to them. How do these standards differ? How do they compare? The paper also describes the approach and issues a control valves manufacturer has to deal with to meet the various requirements on fugitive emissions. It is recognised also that control valves by their function of continuous movement have more tendency to wear out than on/off valves and are therefore more easily subject to packing leakage - from www.valve-world.net.

Video - Sliding-Stem Control Valve Packing - This video gives an excellent description on how spring loaded packing works - from BTC Instrumentation.

Control Valve Packing - Packing is a sealing system which normally consists of a deformable material such as TFE, graphite, asbestos, Kalrez, etc. Usually the material is in the form of solid or split rings contained in a packing box. Packing material is compressed to provide an effective pressure seal between the fluid in the valve body and the outside atmosphere - from The Plant Maintenance Resource Center.

 

Control Valve Fail Safe Position

Fail-safe Control Valves in Case of Fire - W. Schneider - An essential part of equipment safety is the fail-safe position to be maintained when a fire breaks out. In case of pneumatic linear actuators, the fail-safe position must be assumed and maintained when air supply fails or the diaphragm ruptures - from SA Instrument & Control.

Valve Fail Action - Frederick Meier and Clifford Meier - Control valves may fail in various positions -open, closed, locked, or indeterminate. The position of a failed valve can have a significant impact on associated equipment, and therefore, it is of interest to operations personnel - from the ISA and InTech.

Control Valve Actuator Operating Modes - Details on fail safe conditions, fail closed and fail open - from The Plant Maintenance Resource Center.

 

Control Valve Leak Class

FCI 70-2-2013 - Control Valve Seat Leakage - You will have to pay to download this document - This standard establishes six classes of seat leakage for control valves. Also defined are specific test procedures to determine the appropriate class. Included are classes commonly associated with double-port, double-seat or balanced single-port control valves with a piston ring seal or metal-to-metal seats; commercial unbalanced single-port, single-seat and balanced single-port valves with extra tight piston rings or other sealing means and metal-to-metal seats; valves for critical applications where the control valve may be required to be closed, without a blocking valve, for long period of time; and resilient seating control valves with "O" rings or similar gapless seals, among others.

ANSI Valve Leakage Standards - There are six different seat leakage classifications as defined by y ANSI FCI 70-2. These are detailed here - from GEMCO Valve.

Leak Testing of Valves - Standards for Acceptable Rates of Valve Leakage - Covers API standard 598, MSS standard MSS-SP-61, ANSI standard FCI 70-2 and ISO standard 5208 - from wermac.org.

Control Valve Seat Leakage - D Sanders - Tolerance of leakage can vary widely from application to application; tight enough in one case can be overkill in another and insufficient in a third. And to top it off, the various industry standards that classify seat leakage in industrial valves fail to address some of the practical issues that confront valve manufacturers, specifiers and end users. In fact, it is quite possible to successfully specify, manufacture and test a valve according to a well-established industry standard, yet still experience less-than-satisfactory results in the field. This article helps address the technical and practical issues related to seat leakage, discussing the fundamentals behind the governing industry standards and offering guidance that users can apply to enhance initial seat leakage performance and help extend the life of their valve assets - from Hydrocarbon Processing.

Leakage Classifications of Control Valves - Classification of seat leakage through control valves - Control valves are designed to throttle and not necessary to close 100%. A control valve's ability to shut off has to do with many factors as the type of valves for instance. A double seated control valve has a very poor shut off capability. The guiding, seat material, actuator thrust, pressure drop, and the type of fluid can all play a part in how well a particular control valve shuts off - from SVF.

Standards for Control Valve Seat Leakage - This document details the various leakage classes - from Mitech.

Control Valve Seat Leakage Classifications - There are actually six different seat leakage classifications as defined by ANSI/FCI 70-2-1976. But for the most part you will be concerned with just two of them: CLASS IV and CLASS VI. CLASS IV is also known as METAL TO METAL. It is the kind of leakage rate you can expect from a valve with a metal plug and metal seat. CLASS VI is known as a SOFT SEAT classification. SOFT SEAT VALVES are those where either the plug or seat or both are made from some kind of composition material such as Teflon - from The Plant Maintenance Resource Center.

 

Control Valve Noise Calculation and Prediction

Valve Noise Prediction verses Velocity Head Limitations in Gas Applications - Joseph Shahda - Principal Engineer Masoneilan - from Masoneilan.

In recent years, the control valve industry has seen an important debate about the validity of limiting the valve trim exit velocity head to a maximum of 480 kPa in gas and steam applications. This velocity limitation is assumed to provide an acceptable noise level and avoid problems that arise in control valve gas and steam applications. However, in a very large number of applications, adopting a velocity limiting approach may require the use of expensive multi-stage or multi-turn trim designs. This article demonstrates that low noise levels can be achieved without following this overly conservative and expensive trim exit velocity head limitation. It also highlights that having a trim exit velocity head lower than 480 kPa will still generate a very high valve noise level if the valve outlet Mach number is high.

Masoneilan Noise Control Manual - from Masoneilan - This 24 page manual provides comprehensive informative material regarding noise in general and control valve noise in particular. It covers Control Valve Noise, Aerodynamic Noise Prediction, Aerodynamic Control Valve Noise Reduction, Atmospheric Vent Systems, Hydrodynamic Noise and Installation Considerations.

Improving Prediction of Control Valve Noise - from Masoneilan.

Control Valve Exit Noise and its use to Determine Minimum Acceptable Valve Size - Alan H. Glenn - This paper describes general aerodynamic noise generation and prediction and, in more detail, the IEC 60534-8-3 exit noise prediction. It will describe noise generation inside the valve and at its exit, its propagation down the pipeline, and its transmission through the pipe wall and into the outside environment. Several sample cases are included. A simple computer program that could be used to facilitate the calculation of the control valve exit noise for control valves is also briefly explained - from Flowserve and Valve World.

Understanding IEC Aerodynamic Noise Prediction for Control Valves - from Emerson Process Management.

Valves: Noise Calculation, Prediction, and Reduction - Béla Lipták - This section begins with an overview of general noise principles, followed by a description of the types of noise produced by ?uid ?ow through control valves. The discussion of control valve noise mitigation includes both the treatment of the noise source (modifying the valve) and the treatment of the noise path (providing downstream insulation or silencers). Other options include protection of the receiver (by personal protective equipment such as earplugs or earmuffs) or the removal of the receiver (by placing a barrier or distance between the noise source and personnel). The section ends with a discussion about recent improvements in predicting and calculating probable noise levels. Because most valve noise calculation standards avoid excessive detail, only the SI system of units will be used in this section. Users of U.S. Customary units should refer to Appendix A.1 and A.2 for the proper conversion factors, including gravitational units conversions (i.e., gc) when necessary - from Unicauca.

Control Valve Noise - Without meaningful standards being adopted in environmental control (to which also the prevention of valve noise appertains), chemical or petrochemical plants would today not be approved. For this reason, “acoustic planning” for the dominating noise sources is categorically required. This applies particularly for compressors, process ovens, cooling fans and not least for control valves and pipelines. In order to keep the emitted sound power within limits quite extensive corrective measures are required. Since noise attenuation measures within a severe costs/benefit analysis must also make sense, one will only implement noise reducing precautions where it is absolutely necessary. As a result, the competitiveness of the whole enterprise, who wants to construct their plant near a residential area, may be questioned if the permissible sound power level near the plant boundaries has to be especially low - from Samson Controls.

 

Control Valve Performance

A Simple Method to Determine Control Valve Performance and Its Impacts on Control Loop Performance - Michel Rue - A control loop consists of the process, measurement, controller, and a final control element (valve, damper, etc. and its associated equipment such as positioner, I/P). Optimal process control depends on all of these components working properly. Hence, before tuning a loop, one must verify that each component is operating properly and that the design is appropriate. Choosing the optimal PID tuning should be done after making sure all of the other components are working properly. Our experience in the field has shown us that the impact of good tuning is more important than equipment performance itself. We will discuss a method to determine if the valve is performing well and this is done while the process is running. We will demonstrate how a poorly performing valve will have a minimal effect on control loop performance if the tuning parameters are not optimal. However, if a control loop is tuned to achieve performance, the control valve behavior will have a major impact on performance.

How to Achieve Optimal Control Valve Performance - Shawn Anderson and Neal Rineharts - ince control valves are the only devices in the process loop that actually “move” to adjust the process, their performance is critical. The best way to achieve excellent performance is to initially select the most appropriate final control valve for the application and then to maintain its performance over time - from Emerson Process Management.

Evaluation of Control Valve Performance is Necessary in Plant Betterment Programs - Sanjay V. Sherikar - Reproduced with the permission of CCI Sulzer Valves.

 

Control Valve Rangeability

What is Turndown and Rangeability? - A short definition - from Eng Tips.

Control Valve Rangeability - Greg McMillan - There are a lot of ways of looking at rangeability. Nearly all of them lead to the wrong conclusion as to what type of valve is best for process control. Some of the absolute worse valves for control (e.g. on-off piping valves) have the highest stated rangeability. Valve rangeability is particularly important for pH control, batch control, startup, and plant turndown - from Modeling and Control.

Inherent Rangeability - Ideally the open-loop gain remains constant independent of the position of the valve in a closed-loop control system. Unfortunately, this condition is only achieved in rare cases. Every user has already experienced a situation where a control valve at higher travel positions is completely stable, yet permanent oscillations occur at small travel positions. This is caused by a higher gain of the valve and a steeper slope of the valve characteristic. In order to simplify the application and the selection of control valves for the control specialist, certain boundary values for the slope of the inherent characteristic have been set. In this way, the permissible slope tolerance is exceeded if the inclination of the straight line which connects two neighboring measured values (e.g. points 5 % and 10 %), is more than 2:1 or less than 0.5:1. This rule applies for valve characteristics which the control valve manufacturer has specified for the same travel positions in its literature-from Samson Controls.

Limits of Rangeability - The term rangeability was, for a long time, not clearly defined so that it was interpreted in various ways. Even today “rangeability” is often confused with the term „turn-down ratio“ which means the ratio of maximum to minimum flow through a control valve without regarding any tolerances of the inherent flow characteristic, but usually considering flow repeatability. Using this definition and assuming the application of a control valve positioner which guarantees a travel repeatability of 0.5 %, a turn-down ratio of 100:1 and higher can be achieved, while the rangeability, as defined in standard IEC 60534 is not much greater than 15:1. With most trim types, the plug immerses into the seat ring, which requires a minimum gap width, in order to avoid sticking caused by thermal influences or even seizing of seat ring and plug. As a result, an unintentional flow occurs through the gap. This determines the minimum controllable flow and sets natural rangeability limits for any control valve - from Samson Controls.

 

Control Valve Sizing

It is very important that if you are contemplating sizing control valves that you source the latest sizing handbooks and/or software from the manufacturers that you are considering,

Masoneilan Control Valve Sizing Handbook - from Masoneilan - Masoneilan have been taken over by GE and thus the Handbook here may not be the latest edition.

Sizing Control Valves - This article defines a more standard procedure for sizing a valve as well as helping to select the appropriate type - From cheresources.com.

Valve Sizing and Selection - Sizing flow valves is a science with many rules of thumb that few people agree on. This article covers a more standard procedure for sizing a valve as well as helping to select the appropriate type of valve. From cheresources.com.

Nelprof Control Valve Sizing and Selection Software - Apply for the CD from Metso Automation.

Valve Sizing Information from Samson Controls.

Sizing Actuated Control Valves - Do you Really Understand your Application Requirements? - Jody Malo - There are many options and several conditions that need to be considered when purchasing a valve. The more information from the field, the better the choice will be. The ultimate goal is to identify the best valve for the job required at the most economical price. While it’s not rocket science to do this, there is some fundamental information that needs to be taken into account - from Flow Control.

 

Control Valve Styles

Introduction to Valves - By definition, valves are mechanical devices specifically designed to direct, start, stop, mix, or regulate the flow, pressure, or temperature of a process fluid. Valves can be designed to handle either liquid or gas applications. By nature of their design, function, and application, valves come in a wide variety of styles, sizes, and pressure classes. The smallest industrial valves can weigh as little as 1 lb (0.45 kg) and fit comfortably in the human hand, while the largest can weigh up to 10 tons (9070 kg) and extend in height to over 24 ft (6.1 m). Industrial process valves can be used in pipeline sizes from 0.5 in [nominal diameter (DN) 15] to beyond 48 in (DN 1200), although over 90 percent of the valves used in process systems are installed in piping that is 4 in (DN 100) and smaller in size. Valves can be used in pressures from vacuum to over 13,000 psi (897 bar). An example of how process valves can vary in size is shown in Fig. 1.1. Today’s spectrum of available valves extends from simple water faucets to control valves equipped with microprocessors, which provide single-loop control of the process. The most common types in use today are gate, plug, ball, butterfly, check, pressure-relief, and globe valves. Valves can be manufactured from a number of materials, with most valves made from steel, iron, plastic, brass, bronze, or a number of special alloys - from mhprofessional.com.

The following Technical Information is from Samson Controls.

Control Valve Styles - Control valves exist in innumerable styles and options. The most common constructions used in process industries today are discussed. To reach a certain systematic in the description of the various styles, a distinction is made regarding essential criteria and functionalities. A rough overview of the control valves most frequently used is given.

Butterfly Valve Styles - Butterfly valves contain a concentrically or eccentrically oriented disc which can be rotated in a normally sandwich-like housing or body. The angle of rotation is usually 90 degrees for ON-OFF service; for continuous control applications the aperture angle is normally limited to only 60 degrees. Because of the ease of manufacture and the cost-saving construction butterfly valves are - particularly at big nominal sizes and low pressure differentials - a more economical alternative to standard control valves.

Rotary Plug Valves - This valve construction, simply called “the rotary valve”- summarizes different valve styles under a generic term. All of them have one thing in common: a turning valve shaft for adjustments in valve opening. The form of the obturator varies between a simple drilled-through cylinder and a complicated eccentrically positioned plug with a spherical segment surface. To this category also belong armature types which are described as “cock” valves with a cylindrical or conical plug and a special opening cross-section whose profile is authoritative for the flow characteristics of the valve. The so called cock valve, with tapered plug, has been in use for more than 2000 years and was utilized in earlier days - carved out of wood - to tap wine. With the development of new, high corrosion resistant materials like PTFE or PFA which are frequently used for the lining of inferior metallic valve bodies, these well-known constructions have had a renaissance. This principle is used, however, principally for ON-OFF services and only seldom for continuous control applications.

 

Control Valve Trim Materials

Trim Materials

Trim Materials - Gases Versus Liquids - Clean gases are not usually a source of trim erosion, even at high velocities. However, entrained solids or liquid droplets in high velocity gas can wear the trim rapidly. Depending on the fluid’s composition, liquids at high velocity can produce accelerated erosion. For example, at high velocities water causes more damage than lubricating oil. With liquids, another harmful effect is cavitation which can erode most trim material, even hardened trim. Liquid application valves require the use of hardened trim more often than gas application valves - from ValTek.

 

Control Valve Material Selection, Corrosion and NACE Applications

Selection of Suitable Materials for Control Valves - The sizing and specifying of control valves presupposes a high degree of experience in order to meet the requirements in an optimum manner. This applies particularly to the selection of the correct materials for the valve body, valve bonnet and internal parts (trim). A “low cost” control valve, composed of unsuitable materials soon becomes very expensive if it has to be replaced after only a short working life. On the other hand a valve consisting of expensive, exotic materials does not automatically ensure long durability if other important influential parameters have been disregarded. A selection of suitable materials is by no means made easy by the wide spread offering of valve manufacturers. One is reminded of pharmacies who also offer prescriptions identical or at least very similar under different names. As a kind of introduction, a systematic survey of common control valve materials should be examined in order to provide an orientation for valve designers and users - from Samson Controls.

Corrosion and Erosion in Control Valves - Attack by corrosion occurs especially on the inner walls and internal parts of control valves and is therefore often influential in the durability of a component or for the entire valve. If one examines this corrosion process more closely, one finds that insoluble corrosion products forming an oxide layer develop on the material surface. This layer causes a separation between the attacking fluid and the material. This normally very thin layer is designated as the „passivation layer“ which prevents or at least delays a further corrosion. For this reason, high quality austenitic steels are usually treated at first in a pickling plant before any further fabrication. In this passivation process old oxide layers along with scaling and iron dust are removed and a new, precisely controlled passivation layer is formed. It is obvious that this layer must not show cracks and must not be damaged, otherwise the corrosion attack will continue - from Samson Controls.

Valve Materials of Construction for NACE Applications - from Metso Automation.

How to Select Control Valves - This very useful information from the renowned Béla Lipták comes in three parts - Part 1 - Part 2 - Part 3 - When it comes to selecting and sizing control valves, the non-commercial chart in this article not only helps you pick the right one for the job, but also serves as a fantastic reference tool you can download! From Control Global.

Valve Material Selection Chart - from Turnkey Industrial Pipe & Supply.

 

Control Valve Maintenance

Overhaul & Repair Of Control Valves - The repair procedure is as follows; Control Valve Sub-Assembly: (1) Components are marked to ensure correct orientation upon reassembly, and are tested, to reflect an ‘as received’ condition. (2) Complete disassembly. (3) Grit Blast and inspect all pressure containing components' (4) Supply written inspection report. (5) Recut, polish and Lap seat angles. (6) Hone Packing bore area to ensure no leakage through packing box. (7) Remachine flange gasket surfaces. (8) Replace all soft parts and hard parts as required. (9) Reassemble. (10) Test and Calibrate. (11) Paint. Actuator & Associated Instrumentation - (12) Complete disassembly and replace soft parts and hard parts as needed. (13) Reassemble. (14) Set Bench Range and calibrate. (15) Paint. Re-Assembly - (16) Remount all accessories. (17) Replace all tubing and fittings with stainless steel tube/fittings. (18) Test and calibrate valve assembly, including accessories.

Enhanced Maintenance Efficiency with Third-Generation Control Valve Diagnostics - Niklas Lindfors and Juha Kivelä - For more than two decades, maintenance managers and engineers at plants and mills have had a chance to use control valve diagnostics as help when planning shutdown activities. The first diagnostics tools were developed during the 1980s, and since then the technology has taken giant leaps, further providing a wide range of new possibilities. For a rather long time, real-time diagnostic information has been available, including when the process is online, making it possible to predict—and prevent—possible process disturbances. Users are now taking advantage of the additional information available and adopting predictive maintenance strategies to gain more value in the process industry every year. The latest development in the field of diagnostics, the so-called “third generation of diagnostics,” is also playing a role in this transition by further smoothening the shift from traditional corrective and schedule-based to predictive maintenance - from the ISA and InTech.

How to Achieve Optimal Control Valve Performance - Shawn Anderson and Neal Rinehart. - Leaders in the process industries realise that good process control performance is an essential element in achieving world-class reliability as well as optimizing overall process efficiency. Since control valves are the only devices in the process loop that actually “move” to adjust the process, their performance is critical. The best way to achieve excellent performance is to initially select the most appropriate final control valve for the application and then to maintain its performance over time -from Emerson Process Management.

Rethink your Control Valve Maintenance - Neal Rinehart - Learn how new diagnostic tools can help make predictive maintenance a reality - Far too little has been done over the years to sustain the performance of control valves once they go into operation, despite widespread agreement on the impact that valves have on process efficiency. Rather than considering control valves as assets to be preserved, too many plants treat them as liabilities — frequently replacing critical valves during shutdown for no reason other than length of service. As a result, millions of dollars have been wasted and perfectly good control valves often have been discarded - from Emerson Process Management.

The Control Valve’s Hidden Impact on the Bottom Line (Part 1) - Bill Fitzgerald and Charles LindenMany of the profitability issues facing the process industries today can be linked directly to control valve performance. Are there valve-related issues in your plant that you should be concerned about? Part 1 of this article will address dynamic performance of the control valve and how it impacts your bottom line. Part 2 will speak to other valve characteristics that are typically ignored when selecting control valves, such as leakage past the seat, long-term reliability, and maintainability. It will conclude with some case studies that illustrate the dramatic impact that control valves can have on the bottom line - from Emerson Process Management.

The Control Valve’s Hidden Impact on the Bottom Line (Part 2) - Part 1 of this article (VALVE Magazine, Summer 2003) made the case that the control valve, as part of the overall process control infrastructure, is often overlooked when end users consider ways to improve financial performance in their plants. One of the prime reasons for this problem is that control valves are generally selected and maintained as if they were static devices and not part of the highly dynamic process control system - from Emerson Process Management.

Valve Wellness Programs - David W. Douglas - To maximize the utility of diagnostic equipment used in chemical processing, technicians must stretch their knowledge of control valves and related diagnostic equipment that keeps tabs on valve health and safety. Thanks to plantservices.com.

Improving Valve Life and Operating Efficiency The Easy Way - John C. Robertson - Valves are, unquestionably, the most important part of any piping and pumping system because they direct the flow of fluids and regulate temperatures. Properly used and maintained, they can improve process efficiency and lower costs. It is wise to apply the basics of proper valve maintenance in ways that improve their life cycle and operating efficiency. Here are eight often-overlooked valve maintenance basics that can help you do just that. From maintenanceresources.com.

Improving Valve Life and Operating Efficiency The Easy Way - John C. Robertson - Eight often-overlooked valve maintenance basics.

Use of Ultrasonic Analysis in the Testing of Isolating Valves - Offshore installations use a series of isolation valves to divert the flows from the various pumps. One of the main reasons a pump test can "fail", is if the isolating valves are passing. This article describes testing the isolating valves using ultrasonic analysis. Overhaul of an isolating valve costs significantly less than undertaking an unnecessary pump major overhaul.

 

Control Valve for Safety Instrumented Systems Applications

Functional Safety of Globe Valves, Rotary Plug Valves, Ball Valves and Butter?y Valves - This manual is intended to assist planners and operators during the integration of control valves into a safety loop as part of the safety function and to enable them to safely operate control valves. This manual contains information, safety-related characteristics and warnings concerning the functional safety in accordance with IEC 61508 and concerning the application in the process industry in accordance with IEC 61511 - from Samson Controls.

Reliability Data and the use of Control Valves in the Process Industry in accordance with IEC 61508/61511 - Thomas Karte, Eugen Nebel, Manfred Dietz and Helge Essig - IEC 61508 and IEC 61511 are the relevant standards for the speci?cation and design of safety-related control loops in the process industry. Control valves used in these loops play a key role when it comes to determining the safety integrity level (SIL) of the safety instrumented function (SIF). A wide variety of sensors and PLCs, the other key components in the safety loop, are available with validated data concerning their probability of failure. However, this sort of data is only available for a limited number of control valves as statistical proof is dif?cult to obtain due to the multitude of process conditions that exist in the chemical industry. This paper describes the investigation method used for a series of control valves. The user can determine the SIL achieved using this investigation data, the planned plant structure, and an exact analysis of the process - from Samson Controls.

Enhanced Reliability for Final Elements - Process valves, sometimes also addressed as final elements are in many cases the most decisive factor when it comes to calculating the SIL level for a safety instrumented function (SIF). Due to the large variety of conditions of usage in the process industry there is a lack of appropriate data and approved devices. Testing procedures like partial stroke testing can provide enhanced diagnostic coverage and therefore help to get improved reliability data for the total loop. Verification of this 'diagnostic data' and proper integration of these procedures into the safety instrumented system (SIS) and basic process control system (BPCS) environment at the same time poses a challenge. New developments on actors and relevant approvals are presented as well as instrumentation with new functionality to support diagnostic coverage, different topologies for connection to SIS and BPCS are discussed - thanks to SA Instrumentation and Control.

 

Split Range Control Valves

Implementing MPC to Reduce Variability by Optimizing Control Valve Response - Ever had a problem with split range valves, this paper may just help! Thanks to www.controlglobal.com.

Split Range Control Valves - This tutorial details just what split range is along with some examples - from Contek Systems.

 

Control Valve Actuator Design and Operation

The Fisher Control Valve Handbook - This superb 295-page PDF whitepaper is a control valve resource that has been consistently updated for 30 years. It contains vital information on control valve performance and latest technologies. Thanks to Emerson Process Management.

Control Valve Actuator Bench Set Requirements - Jerry Butz - Control Valve “Bench Set” is an often-misunderstood point of confusion, and sometimes incorrectly described part of a control valve’s actuator specifications. But not understanding it can set one up for a failure in the form of a mis-sized actuator and spring. Maybe this information can help to clear the cloud of confusion and make it easier for engineers, technicians, and operators to understand - from Flow Control.

Understanding Control Valve Bench Set - Dave Harrold-from Control Engineering.

Control Valve Actuators - This is ICEweb's Technical Information page on Control and Quarter Turn Valve Actuators.

Control Valve Actuators and Positioners - Control valves need actuators to operate. This tutorial briefly discusses the differences between electric and pneumatic actuators, the relationship between direct acting and reverse acting terminology, and how this affects a valve's controlling influence. The importance of positioners is discussed with regard to what they do and why they are required for many applications-from Spirax Sarco.

Control Valve Actuator Options - Today’s Actuators Offer Imposed Performance With Lower Life-Cycle Costs. The Challenge Is Choosing the Right One for the Application - George Ritz - Over the past several years, valve actuators have received relatively little attention while process control specialists concentrated on controllers, sensors, and other components of the control loop. This is borne out by the unglamorous nickname “pig iron” assigned to the actuator/control valve unit. With the onset of the smart-valve generation, it suddenly appears that the control valve actuator may get more respect along with its new electronics degree - from CCI.

Linear Pistion Actuators - Samy, Stemler - High Reliability of actuation is of paramount importance in the nuclear power industry. Pneumatic actuators form the largest installed base with many in safety significant applications. This paper addresses the issues related to actuation, such as available Thrust, Stiffness, Sensitivity, Hysteresis, Dead band, Dynamic Stability and a sizing example. This paper also presents comparisons between various types of linear actuators and their relative advantages and disadvantages. Also presented will be evaluation techniques for troubleshooting actuator problems and improving plant performance - from CCI.

Closed Loop Breathing - This is a technique to ensure that corrosive or saline air cannot enter the internals of the valve on the breathing side of the valve. It is very popular in the Offshore Oil and Gas Industry and on Coastal Refineries etc - thanks to Rotork for this excellent schematic.

How to Select an Actuator - Wayne Ulanski - As the process industry continues to achieve more efficient and productive plant design, plant engineers and technicians are faced, almost daily, with new equipment designs and applications. One product, a valve actuator, may be described by some as simply a black box, having an input (power supply or signal), an output (torque), and a mechanism or circuitry to operate a valve. Those who select control valves will quickly see that a variety of valve actuators are available to meet most individual or plant wide valve automation requirements. In order to make the best technical and economical choice, an engineer must know the factors that are most important for the selection of actuators for plant wide valve automation. Where the quality of a valve depends on the mechanical design, the metallurgy, and the machining, its performance in the control loop is often dictated by the actuator - from SVF Flow Controls, Inc.

Control Valve Actuators: Their Impacton Control and Variability - Chris Warnett, In a process plant, the general function of a control valve is to restrict the opening of the valve so it affects the flow or pressure of the liquid or gas that is passing through it. In anygiven application, an installed valve, whether it is a rotary or sliding stem valve, has one fundamental variable - the position of the moving element. That single moving element determines the exposed orifice that allows greater or lesser flow through the valve, which inturn provides the control of the process. The valve itself may be extremely sophisticated with exotic body and seat material, or it may have complex flow patterns that allow for a high pressure drop or some other function.However, the fundamental requirement to move the valve stem to position the control element remains the same regardless of whether it is a simple or a sophisticated valve.A control valve actuator is used to move the valve stem (which is attached to the internal control element) to the desired position and hold it in place. In addition to the act of moving and holding positions, there are many other parameters to that movement which determine the best type of actuator that should be used for every specific application. For example, other important considerations might include speed, repeatability, resolution, and stiffness - from Rotork Process Controls and Valve World.

Valve Actuator Accessories

The following links are provided thanks to Austral Powerflo Solutions.

Rotary Limit Switch Boxes - Rotary limit switch boxes provide a visual and remote electrical indication of quarter turn valve/actuator position (ball, butterfly and plug).

Bolt Switches - "Bolt" switches are magnetic proximity switch suitable for any type of position indication.

Valve Position Indicators - The 3D Series namur indicators provide high visibility verification of valve/actuator position. The indicator features a rotor with red and green quadrants that rotate to indicate valve open and valve closed positions.

 

Butterfly Control Valves

Why a Butterfly - Vinod Bhasin -thanks to Sigma Tech- This is a pretty old document but has some good information.

Application of Butterfly Valves for Free Discharge, Minimum Pressure Drop, and for Choking Cavitation - Flow Component and Control valve Research -Utah State University.

 

Control Valve Applications

The following links are from Masoneilan.

Avoid Control Valve Application Problems with Physics-based Models - Kinetic energy criteria have many limitations- from Masoneilan - This article explores the rationale for KE limitations and demonstrates that KE criteria often provide very rough approximations of the actual physical phenomena that cause valve problems.

Boiler Feedpump Recirculation Valves

Condensate Pump Recirculation Valve

De-Aerator Level Control

Natural Gas Storage - Valve Solutions - by Larry Swartz.

Other Links

Getting Optimum Performance through Feedwater Control Valve Modifications - by Brian Leimkuehler and Sanjay V. Sherikar - Reproduced with the permission of CCI Sulzer Valves.

The Application of Control Valves to Compressor Anti-surge Systems - E.W.Singleton - Pipelines transporting gases and vapours are invariably dependent on centrifugal or turbo-compressors for the propulsion of these fluids. Under normal operation, with the compressor running at any constant speed there is a specific relationship between the pressure head across the compressor and the flow through it. But this stable relationship can be disturbed by sudden changes in flow, pressure and density, usually caused by sudden variations in demand downstream of the compressor or in the case of systems requiring multiple compressors a disturbance can be caused by the switching of compressors in and out of service. All these can give rise to formidable pulsations of pressure and flow, better known as a surge. Under surge conditions the compressor may run erratically and a situation can arise where the pressure build up in the downstream pipe may overcome the delivery pressure of the compressor resulting in a flow reversal, reversing the compressor and causing mechanical damage - from Koso Kent Introl.

Control Valves for Pump Protection (Recirculation) Service - EW.Singleton - This paper discusses the essential procedures involved in the application of control valves for the protection of pumps operating at low flow conditions. Automatic Recirculating Valves (ARC Valves), although they do not fall into the category of control valves, do play an important role in pump protection, so a reference to these is also included - from Koso Kent Introl and Valve World.

Control Valve Sourcebook - Pulp & Paper - This Control Valve technical reference is focused on the selection, use and applications in a Pulp Mill - from Emerson Process Management.

Predicting Control Valve Reliability Problems and Troubleshooting in Petrochemical Plants - Critical Outlet Velocities - The Hidden Valve Enemy - Holger Siemers - In the complex area of the prediction control valve reliability, the various aspects of the cost-driven market, which have forced valve manufacturers to develop valves for typical market segments, have to be looked at. In the oil and gas market, a signi?cant portion of valves are severe service valves with high power consumption. A good balance between commercial aspects and necessary safety requirements for the long-term has to be found. This article recommends steps for long-term control valve reliability - from Samson Controls.

Control Valve Design Aspects for Critical Applications in Petrochemical Plants - Holger Siemers - Samson Controls - With three decades of experience in demanding applications, Mr Siemers has a deep appreciation of developments and trends in sizing control valves. In this paper, he reviews the past, present and future of valve design and sizing, taking all-important issues such as increasing cost pressure and time pressure into account. This paper is presented in two parts: firstly, how to use manufacturer independent software to analyse given or calculated plant parameters in more detail from an overall pointof view with a complete power check and optimizing possibilities. Some case studies are also discussed. The second section, scheduled for a future issue, includes information on to design, size and use severe service control valves with good performance for long maintenance intervals. Different philosophies of valve design (plug design), pressure balance systems, stem sealing, actuator sizing, cost philosophies for" high end" applications are discussed. The paper covers:

Accurate sizing & software tools.
Energy saving by plant and valve optimization.
Debottlenecking: Can the old valve do the new job ?
Predictable troubles with control valve sizing in case of sub-critical flow conditions and in case of flashing.
Control valve failures & troubleshooting.
The hidden valve enemy: Critical outlet velocities need to take priority.
Fugitive emissions philosophies for control valves.
Actuator sizing philosophies.
Control valve design and cost philosophies for "high end" applications.

A Valve as a Flowmeter - Because valves are already installed for process control, process optimization and performance can be further improved by using control valves to measure the flow rate - Technical information from Metso Automation.

 

Control Valve Positioners and Accessories

Smart Valves, Positioners and Flow Conditioning Technology - One of the newer devices that offer improved performance of control valves is the smart positioner. A smart positioner is a microprocessor-based electronic positioner that derives benefit from digital programming to obtain improved positioning performance. Some models offer predictive maintenance and diagnostic benefits as well. An advantage of the smart positioner is that it may be programmed to use a position control algorithm to achieve better dynamic response than standard pneumatic positioners.- from Masoneilan.

Doing Business Differently-Digital Positioners - from Masoneilan.

The Next Generation of Smarter Valves part 1 and part 2 - By Béla Lipták, thanks to ControlGlobal.com.

Smart Technologies Sustain Plant Reliability, Help Control Costs - Todd Gordon - This article highlights the benefits of DVC technologies in a power plant - from Emerson Process Management.

Positioner and Actuator Operating Modes - The terms "direct" and "reverse" are frequently used when discussing control valves, positioners, and controllers. While the definitions of direct and reverse seem pretty straightforward, they cause quite a bit of confusion - especially when split-ranging is done. From The Plant Maintenance Resource Center.

Mission Possible - Analog-to-Digital Valve Upgrades - Sandro Esposito - A transformation is underway in process control, as a wide variety of new digital devices have been introduced in recent years, and a growing number of facilities have installed them. The transition is still a work in progress, however. Some process control facilities have simply been a bit slower to adopt digital valve positioners, for example, as they seek to become more comfortable with this unfamiliar technology. Others have made the switch to digital devices, but have maintained an “analog mindset” and use the digital positioners as they did their analog predecessors. The status quo is maintained and technologies that could help plant operators save time, money and frustration while potentially improving product quality and enhancing safety, are either not adopted or are underutilized. The first step in making the transition to digital valve positioners is understanding how they can be easily and cost-effectively implemented in a facility. This article will begin to bridge that gap by reviewing the various technologies available and highlighting the steps that should be taken to help ensure a successful transition. In addition, it will explain how plant operators can achieve what many consider to be a “mission impossible” - i.e., “hot cutover,” or switching to a digital valve positioner while the process workflow continues uninterrupted - from Kentrol and Flow Control.

Upgrading to Digital Positioners on Feedwater Regulating Valves - Chuck Linden and Bill Fitzgerald - Positioner problems such as spool valve fretting, feedback arms and linkages have been an ongoing issue in the Nuclear Industry. The decision was made to look at new technology in an attempt to eliminate the problem(s). The option of a digital positioner was selected for the upgrade. Several features such as remote mounting capability, on board diagnostics capability and allow integration to a future Digital Process Control System modification at Fort Calhoun Station. Based on the experiences at Fort Calhoun Station and discussions with plants installing digital positioners on Feedwater Regulating valves many of the challenges were similar. This presentation is important because some of the issues were technical in nature but many revolved around cultural paradigms and work practices. To gain the full advantage of equipment upgrades such as this one, one must be ready to address culture and to change work practices - from Fisher.

Intrinsic Safety and Flameproof Enclosure - An Impossible Team in Explosion Protection? - Dipl.-Ing Guido König and Prof. Dr.-Ing. Heinfried Hoffmann - The increasing application of digital field devices in process automation has revived the discussion about the best types of protection for instrumentation used in hazardous areas. The large number of electrical components integrated in microprocessor based devices requires more precautions to be taken per field device in order to ensure explosion protection. A positioner designed for pneumatically operated control valves is used to demonstrate different solutions - from Samson Controls.

Smart Valve Positioners and their Use in Safety Instrumented Systems - Thomas Karte, Jörg Kiesbauer - As part of efforts to reduce life cycle costs of control valves in the process industry, smart electro-pneumatic positioners play an important role due to their self-adaptive features and their highly developed diagnostic functions. Their use can lead to decisive improvements in availability and reliability. To make full use of this potential, which has often been discussed in theory in the past but hardly been put into practice to date, NAMUR Recommendation 107 and Guideline VOl 2650 provide information on the scope of diagnostics and the generation of alarm states. Applications in safety instrumented systems are of particular interest as smart positioners are used more and more with on/off valves in place of classic solenoid valves. In the process industry, the use of on/off valves in safety instrumented systems is governed by the IEC 6 1511 standard. The basic principle behind this standard is the safety management life cycle, which can be effectively supported by the diagnostic functions of positioner - from Samson Controls.

Solenoid Valves

Solenoid Valves - ICEweb's solenoid valve page has a vast amount of information on Solenoids.

 

Control Valve Education

Professional Certificate Of Competency in Control Valve Sizing, Selection And Maintenance - Control valves are the workhorse of our facilities, continually functioning to ensure our systems work as intended. A properly specified, engineered, designed, installed, and maintained control valve can be one of the most profitable investments a facility can have, while a control valve that "does not work well" can be an increased risk of injury (more exposure of maintenance personnel working on the valve), and disruption to your system. With today's focus on data management, the control valve is the part of the control loop that not only requires integration with modern data collection methods, but also involves mechanical features (moving parts, exposure to process fluids, material selection issues) as well as occupational health and safety issues not associated with other parts of the control loop (such as noise).Often the benefits of modern SCADA systems can be lost with inappropriate or minimal attention to the control valves. This comprehensive certificate course covers the essentials of control valves and actuators. With this knowledge, the user is better placed to fully realize the full potential and benefit of any control system. Selections of case studies are used to illustrate the key concepts with examples of real world working control valves. The course is aimed at those who want to get a solid appreciation of the fundamentals of their control valve design, installation and troubleshooting - from EIT.

 

Self Operated Regulators

For Details on Self Operated Regulators see ICEweb's Pressure Regulator Page.

 

Emergency Shutdown and Blowdown Valves

ICEweb's comprehensive page on ESD and BDV valves contains a super vault of technical papers on this important subject.

 

Composite Valves

Looking for a valve without corrosion problems? These valves made from plastics and potentially using Nanotechnology techniques may just solve them.

 

Specialist Power Plant Valves

These valves are specific to those power plant issues such as de-superheaters, steam service etc.

 

HVAC Control Valves

HVAC Control Valves Ball vs. Globe - No longer a Cost Issue - In the past, ball valves had been attractive to HVAC control contractors primarily because they appeared to be half the price of a comparable globe valve. However, this included the purchase price of the valve only, and not the costs of extra pipe reducers and added installation time. That said, with the advent of new ball valves and more competitively priced globe valves, the decision on whether to use a globe or ball valve is no longer dictated by price. This paper addresses some technical differences between ball and globe valves and makes recommendations on factors to consider when selecting the proper valve - from Siemens.

Selecting HVAC Control Valves - from Siemens Building Technologies, Inc. The Tech Tips section from page 90 is particularly relevant.

HVAC Control Valve Characteristics - Amrish Chopra - In HVAC systems, control valves are primarily used to control the flow of chilled water, hot water or steam. To understand the importance of valve flow characteristics in HVAC control it is necessary to understand valve construction, type of valve flow characteristics and few basics of control theory - From - Anergy lnstruments.

Evaluation of ControlValve Performance is Necessary in Plant Betterment Programs

Sanjay V. Sherikar, Ph.D., P.E.
CCI
22591 Avenida Empressa
Rancho Santa Margarita, CA 92688
Phone (949) 858 1877
Fax (949) 858 1878
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it..

Abstract

Control valves affect the performance of power plant in terms of output, heat rate, reliability and availability because they are the final control elements in the operation. Therefore, critical evaluation of control valves must to be an integral part of any plant betterment program because the ultimate goal of such efforts is to improve the efficiency and reduce costs. Even control valves in the few severe service applications, which affect efficiency more than the rest of the valve population, have traditionally not been included in such efforts.

Recent studies indicate that eliminating control valve problems alone can improve the heat rate of power plants in the range of 2% to 5%. The elements that are critical in realizing the potential benefits are: analyzing the whole system and quantifying the losses, identifying the root causes of the problems causing these losses and then, finally, eliminating the root causes of those problems. Methods to estimate loss due to control valve non-performance have to be judiciously applied, and sometimes developed, on a case-by-case basis, as shown by examples in this paper. The commonly observed causes of valve problems are discussed, followed by practical strategies for implementing solutions to the valve problems.

Besides the potential for heat rate and efficiency improvement, solving severe service valve problems also removes a major obstacle for the plants to operate for longer intervals between outages, reduce scope of outage maintenance and provides opportunity to upgrade systems to modern practices.

Introduction

Operating power plants reliably, at full power and maximum efficiency, is desirable because of the great economic significance. This affects the economics of the individual power station, the electric utility and the whole economy that depends on it. Therefore, a great effort is made at the design stage to ensure efficient and reliable operation of these plants on a daily basis.

Key parameters are monitored for overall plant efficiency as prescribed by the designers of each station. Traditionally, severe service control valves have not been included in the efficiency analysis. This may have been due to a combination of factors - their treatment only as “necessary evils” in control, poor recognition of their contribution to plant efficiency and, perhaps, a lack of systematic methods in quantifying their effect on efficiency. However, there is a growing awareness in this regard. This is reflected in the critical scrutiny given to severe service control valves, as opposed to general service valves, when building new power plants and in improving efficiencies of existing power plants.

Control valves are the final control elements in the operation of a power plant. Therefore, plant efficiency is directly affected by non-performance of the valves, either in terms of output or in terms of reliability and availability. Figure 1 shows a simple process in which a control system which generates the control signal, a valve which operates according to the signal and then a feedback sensor which relays the parameter being monitored to the control system. The weakest link in this control loop will be the limiting factor in the control of such a process. Even the sophisticated digital control systems (DCS) or modern feedback sensors cannot make up for the limitations in the performance of a control valve.

Figure 1. Simplified diagram of process control.

Severe Service Valves

Of the hundreds of control valves in any power plant, some valves experience tough operating conditions either at all times or under some operating conditions. These are known as severe service valves. Although they are few in numbers, they pose challenges to maintenance and operation. In most cases, problems are caused by the misapplication of general service valves in severe service duty. These severe service applications also affect efficiency more than the rest of the valve population. Conversely, for an existing power plant, eliminating problems in the severe service valves offers one of the quickest and effective means of improving its efficiency.

While contributions to plant efficiency loss from individual valve applications may be small, together they all can add up to be a significant value. When the invisible effects of the valve problems are taken into account, the net impact is even greater.

Severe Service Valve Problems and Their Impact on Plant Efficiency

The most critical factor used to judge the performance of a power plant is the heat rate of the unit. To achieve operation at lower heat rates the effect of controllable parameters on the plant heat rate should be quantified. Controllable losses typically are monitored and efforts are made to reduce these. By definition, and as a minimum, the fuel-cost penalty due to the controllable losses, which has direct impact on the efficiency of the unit, can be eliminated with proper solutions.

Examples of severe service control valve applications in the main power-generating loop in nuclear power plants are: main feedpump (MFP) minimum flow control, feedwater control, turbine bypass, atmospheric dump and emergency heater drains. In addition, there are many other severe applications in various other systems in nuclear plants, such as the residual heat removal (RHR), high pressure core injection (HPCI), service water, high pressure injection (HPI), reactor coolant system (RCS) and chemical volume control system (CVCS).

The typical problems caused by incorrect technology in severe service valves are:

• Premature trim and body erosion due to lack of control of fluid velocity along the flowpath
• Poor shutoff capability, i.e. leakage through the valve under closed condition, because of inadequate actuator thrust, damage to the sealing surfaces caused by high velocities and improper calibration
• Process controllability problems with the valve operating at lower openings
• Poor dynamic response

Most often, the visible effects of control valve problems are:

• Loss in production capacity
• Occasional plant trips
• Frequent maintenance
• Safety concerns

In addition, there are other costs, which may sometimes be invisible, because of the valve problems:

• Penalty in heat rate/ high operating cost
• Longer time for startup
• Lower Unit availability

• Collateral damage to other expensive plant equipment (e.g., turbine, heater, boiler tubes) because of occasional transients that cause operation beyond normal operating conditions

• Low flexibility in operation, e.g. part-load operation, or sliding pressure mode, in fossil power plants may not be possible even when it is desirable.

Expression of Loss Due to Control Valve Non-performance

There are several ways of expressing the estimates of loss due to control valve non-performance. The most direct, and perhaps the simplest, measures are those of generation capacity in MWe, heat rate and overall cycle efficiency.
In a majority of the cases, the plants can operate at the rated generation capacity because of built-in over-capacity in the auxilliaries, burning more fuel and the ability to replenish the losses in sub-systems. In such cases, the losses may be expressed in terms of Btu’s/hr directly, or in terms of “equivalent MWe”. In this context, equivalent MWe is defined as the additional electrical power output that the plant could generate by eliminating the existing control valve problems if there were no other limitations.

For quantifying inefficiencies due to control valves, the operational losses due to control valve problems can be categorized as follows:

• Primary losses of energy

• Secondary losses of energy

Examples of primary losses of energy are leakage or flow from turbine bypass valves, emergency heater drain valves, main steam drain valves and boiler feedpump recirculation valves. In general, it includes all “high-energy dump valves”, i.e. those with high energy at the inlet and dumping to atmosphere or the condenser or a drain tank, that should be shut tight during normal operation. The energy loss is easily quantifiable when the process parameters and leakage flow estimates are available. At best, more fuel has to be burnt to make up the loss of energy in the leakage flow; at worst, the plant’s load is limited and the maintenance cost is high.

In fossil-fired power plants, the primary losses also include the effect of leaking attemperator spray valves. In this case, the leakage flow causes the steam temperature to drop. As a result the boiler must be fired harder to raise the steam temperature to the set value. The penalty in heat rate as a result of this can be translated to efficiency loss. This loss is quantifiable from the data provided by the plant designer at the time of commissioning.

Secondary energy losses include those due to unavailability because of control valve problems, loss due to degraded operation because of poor controllability and second-order effects of control valve problems. These can be quantified using historic data of plant operation. Judgement based on prior experience, and understanding of plant operation, is required for estimation and to assess if they are significant.

Methods for Estimating Penalties Due to Control Valve Non-performance

Calculation of energy losses due to control valve leakage first require estimation of the leakage rate. Some of the methods that have been used for this purpose are based on:

1. Anticipated degradation of the specified shutoff leakage class

2. Typical damage observed in similar applications

3. Actual damage observed in the specific service

4. Process indications, pressure, temperature etc., in the system

5. Heat & mass balance analysis of well-defined control volume in the system.

The order above indicates increasing reliability of estimates going down the list.

Calculation Based on Anticipated degradation

As a general rule, “high-energy dump” valves are closed during normal operation and should seal very tightly when shut. In severe service applications, even a tiny leak path creates high velocity jets of leakage flow that damage sealing surfaces progressively, thereby creating a major leak. The ANSI class IV shutoff specification allows a maximum leakage equivalent to 0.01% of the capacity, Cv, of the valve. While this may seem pretty tight, this performance for a severe service application may be achieved in factory test and not much beyond that. In practice, the degradation of shutoff of such severe service valves has been observed to cause leakage flow equivalent of 1 to 5% of the valve capacity, Cv.

Calculation Based on Typical Damage

Examples of typical trim damage in severe service control valves are shown below in Figures 2a-c. Such damage to the sealing surfaces of a control valve can be translated into area of the leak path for which the leakage flow capacity, Cv, can be readily calculated. In such instances, the actual leakage flow when the valve is closed can be calculated from the known process parameters upstream and downstream of the valve, and from the leakage flow Cv.

If the typical damage is known from previous maintenance history, it can be used directly. A calculation based on this method is shown here for the case of a main feedpump (MFP) recirculation valve in a pressurized water reactor plant.

Case - MFP recirculation valve : The cage from this valve after one cycle of operation is shown in Figure 3. Measurements of the damage to the sealing surface indicate that its total cross-sectional area to be 0.087 sq. in. Then, the flow capacity (Cv) of the damaged area = (0.087 sq.in.)(31) = 2.7 For upstream flow conditions of 1150 psig and 431 oF, and condenser pressure downstream , Leakage flow, Q = (Cv)(DP/G)1/2 = 83.1 gpm, where G is the specific gravity. This translates to approximately 35,100 lbs./hour of leakage. The energy of this leakage flow is being lost from the cycle. The enthalpy upstream is known from process conditions to be 409.7 Btu/lbm; the enthalpy of the condensate is 69 Btu/lbm. Therefore, the estimated energy loss is = (35,100 lbs/hour)(409.7-69) = 3.9 MW-thermal This is loss per valve. At 33% overall efficiency, the loss in electrical power is 1.3 MWe. Since there are 2 valves per Unit, the total loss is 2.6 MWe for the Unit.

Is this estimate credible? - It has been reported [Reference 4] that PSE&G, Salem, gained 2 MWe per Unit by eliminating the leakage in their MFP recirculation valves!

Figure 2 (a) to (c), clockwise from top

When such information on damage to the sealing surfaces is lacking, prior experience of typical damage in the specific application can be used.

As a quality check, the leakage Cv should be compared to the full Cv of the valve.

Figure 3. Damaged trim from main feedpump (MFP) recirculation valve showing areas of damage on the sealing surface. The depth and width of individual damage locations were measured to arrive at an equivalent leakage area.

Calculation Based on Available Process Indications

In some instances, pressure and temperature indications may be available across an element, which is located downstream of the leaking control valve, and which offers resistance to flow. In such cases, the geometry of this component, or its design data, may be used to calculate its equivalent flow capacity, Cv. From this and the process indications available, leakage flow can be estimated. At times, a flow transmitter is located in the same line as the control valve. Then such valves leak, the leakage can be read directly from this indication.

Estimate Based on Heat and Mass Balance

This requires a true system analysis and use of data that is available at the plant. In this type of procedure, a control volume is defined in the vicinity of the subject valve(s) and conservation principles are applied using the actual process conditions at a given time.

Figure 4 shows the final result for such an analysis for a start-up system in a fossil power plant. To arrive at this heat balance, mass balance and power balance equations were applied to the control volume shown, and also to heaters 1 &2 and the HP-IP turbine.

Estimation of Secondary Losses

Secondary losses, which include those due to unavailability and degraded operation resulting from poor control valve performance, can be estimated from power plant’s operational history and records. They are silent MW-killers as well and have to be estimated on a case-by-case basis.

Non-operational Costs

Besides the operational inefficiencies as described above, there are additional costs resulting from control valve problems. These include the cost of maintenance, spare parts, inventory, and most importantly the additional time required to attend to the problematic valves during planned shutdowns. The collateral damage cause by valve problems must also be taken into account in the cost-benefit analysis of the solution.

Recovering Losses due to Valve Problems

When a control valve continues to be problematic despite good maintenance practices and skilled staff, it is the first clue that incorrect technology is being applied in that service, which is not suitable for the specific application requirements.

Figure 4: Final mass balance between boiler inlet and IP turbine outlet to determine total leakage from the control volume.

Identifying the root cause is the first step in solving problems in an existing valve and recover the losses that they cause. Then follows the step of ensuring that the correct valve technology is used in the case of new applications.

All severe service applications are not the same. This makes the details of each application all the more important. A discussion of the causes of valve problems in severe service applications, and the importance of addressing their root cause, can be found in References 1-3.

System Improvements

The power plant designers use the best technology for various systems and sub-systems that is available at the design stage - sometimes! Where that is not the case, and just with the advancement in technology over the years, plant betterment programs are an excellent opportunity to simplify systems and modify operations where it is beneficial.

Figures 5 (a) and (b) show simplification of controls in the feedwater system in a combined cycle plant. With the correct technology for control valves, this solution reduces valve maintenance drastically while solving root cause of problems specific to those valves.

Some examples of system improvements that have been realized by different power plants are:

• Flexibility in operation,
• Elimination of valves and some of the system components altogether,
• Combining the function of two or more valves into one,
• Incorporating warming flow function in upstream valves instead of separate warming lines,
• Elimination of safety-related problems.

Figure 5a: Schematic of the flow diagram showing the locations of severe service valves

Figure 5b: Simplified feedwater system and the locations of severe service valves.

Conclusions

In conclusion,

• Control valve performance must be evaluated as part of any plant betterment program. Such an effort, especially focussed on severe service valves, can improve plant in plant efficiency and reliability.

• Evaluation of system as a whole is a key ingredient in eliminating losses due to severe service control valve problems.

• Evaluation of control valves in plant betterment programs provides opportunity to upgrade systems to modern practices.

• Quantification of losses due to control valve problems is possible by evaluating the system operation and the data that is generally available.

• Elimination of severe service valve problems removes a major obstacle for the plants to operate for longer intervals between outages, and/or reduce outage maintenance.

References

• Sherikar, S.V. Technology In Severe Service Control Valves, 15-th Annual Air-Operated Valve Users Group (AUG) Meeting, Tuscon, AZ, June 9-12, 1998.
• Miller, H.L., and Stratton, L., Fluid Kinetic Energy As A Selection Criteria For Control Valves, ASME Paper FEDSM97-3464.
• Miller, H.L., Frequent Control Valve Problems, Seventh EPRI Valve technology Symposium, Incline Village, NV, May 26-28, 1999. [to be presented]
• Coleman, M., 15-th Annual Air-Operated Valve Users Group (AUG) Meeting, Tuscon, AZ, June 9-12, 1998. [private communication]

Fire Safe Control Valve Actuators

An essential part of equipment safety is to be able to maintain the fail-safe position when a fire breaks out. In case of pneumatic linear actuators, the fail-safe position must be assumed and maintained when air supply fails or the diaphragm ruptures.

Usually, springs are used to perform this task. They force the valve to move to the fail-safe position when dangerous situations emerge or damages occur. On failure of air supply, the Actuator springs act against the pressure of the process medium on the plug to move the valve to the fail-safe position and keep it there.

Fig. 1: Control valve with pneumatic actuator

When a fire breaks out, the fail-safe position of the pneumatic actuator will be adversely affected. The high temperatures cause the springs to lose their force. With increase in time and temperature, the springs can no longer keep the valve in its fail-safe position. In the case of “Fail-close“ action, increasing leakage cannot be avoided.

Fig. 2 shows how a preloaded spring loses its force under the influence of time and temperature.

Shortly after the fire has broken out, the spring force decreases considerably. As a result, the ability to keep the valve in its fail-safe position during the fire will be lost within a short period.

The loss of rigidity and the considerable decrease of force are caused by recrystallization processes within the material structure of the spring.

The use of conventional fire protection systems, such as coatings, do not provide decisive advantages since springs are moving components and subject to dynamic stress. Coatings cannot sufficiently retard the loss of force either.

Safety cartridge

The problems discussed above were addressed by developing a thermostatic system. This passive system was designed to recognize non-typical temperature rises and respond to them actively. A quite simple cartridge element, was developed to perform this task.

This cartridge consists of two metal cylinders sliding freely within each other. It is filled with intumescent material which is composed in such a way that it reacts on reaching the release temperature, within certain boundaries, and then increases the force it exerts.

Fig. 3: Schematic of safety cartridge

The cartridge is made up of a two-piece cylindrical case. The enclosed cylindrical chamber contains the intumescent material. This material is composed in such a way as to ensure activation of the cartridge before the diaphragm of the pneumatic actuator is destroyed by high temperature. The increase in volume causes the cylinders to move in opposing directions. During this process, considerable forces are developed. The operating direction of the cylinders corresponds to that of the springs, thus opposing their gradual loss in strength. Installed in actuators with safety equipment [5], these patented cartridges compensate for decreasing spring force.

The safety cartridge is heated according to the unit-temperature curve in which the development of temperature over time is plotted in accordance with DIN 4102, Part 8 [6].

Installation

The design of this irreversibly operating cartridge is simple and allows retrofitting into already installed pneumatic actuators.

To do this, the safety cartridge must be installed in the center of the actuator springs. The mounting position of the pneumatic actuator is not important, the cartridge can always perform its task of closing the valve in the event of a fire.

The selected overall length of the cartridge does not affect the travel or operating range of the springs at standard ambient temperatures. Only in the event of a fire does the cartridge become effective, reacting to the unusually high temperatures.

Fig. 6, a: Arrangement of cartridges in the pneumatic actuator (sectional drawing) Fail safe, shaft extends.

a) Actuator springs “fail-close“; safety cartridges in deactivated state

b) Safety cartridges after temperature rise

Fig. 6, b: Arrangement of cartridges in the pneumatic actuator (sectional drawing) Fail safe, shaft retracts.

a) Actuator springs “fail-open”; safety cartridges in deactivated state

b) Safety cartridges after temperature rise

Simulation of a fire

A control valve equipped with a safety cartridge was subjected to a simulated fire test.

Technical data of the control valve used in the simulation:

Valve:	SAMSON, Type 3241, nom. size DN 25, nom. pressure PN 40
	Characteristic:	equal percentage
	Valve plug:	lapped-in-metal
	Plug material:	Cr steel, WN 1.4006
	Seat material:	Cr steel, WN 1.4006
	Body material:	GS-C 25, WN 1.0619
Actuator:	SAMSON, Type 3271 Pneumatic Actuator
	Effective diaphragm area:	350 cm²
	“Actuator stem extends”
	Signal pressure range:	0.6 to 3 bar
	Material:	St 1203
	Diaphragm:	NBR with polyester fabric

The test aimed at maintaining the tightness of the valve over 30 minutes minimum with constant system pressure acting on the valve. The time span is based on the specifications given in BSI 6755/2 [7].

The test valve described above was heated in a test oven according to the unit-temperature curve. The pneumatic actuator was equipped with 6 cartridges installed in the actuator spring assemblies.

The valve contained water. During the heating phase, steam was produced. A pressure regulator installed outside the test room maintained a constant system pressure of 30 bar. Prior to starting the test, a pump had been used to produce this pressure. Downstream of the seat/plug restriction area, the valve was open to atmosphere.

The temperatures in the test oven and at the pneumatic actuator were measured via thermocouples.

The temperature increase over time in the test room and in the pneumatic actuator was correspondent to the unit-temperature curve (see Fig. 5). The system pressure of 30 bar in the valve upstream of the seat remained constant during the entire test procedure.

Fire Test Summary

As expected, the rubber diaphragm was completely destroyed at the end of the test. With the exception of the springs, none of the metallic components showed any visible damages or deformations.

The task, to provide tight shut-off against the 30 bar pressure throughout the test during the high temperatures of a fire, was fulfilled for the entire period of high temperature supply.

Reversing operating direction

Apart from safety cartridges, there are additional solutions that can be integrated in the pneumatic actuator for safety.

Where a valve may normally be required to “fail open”, it is possible to use a preloaded spring assembly released at a pre-set temperature to oppose the standard fail-safe position.

This patented method [8] is composed of preloaded spring discs which act in opposition to the standard actuator springs. Upon release of the spring discs, the standard fail-safe action is reversed.

The spring discs are bound together by a solder strip. The selection of the type of solder determines at which temperature the spring discs are released to act as an additional safety device. The solder joint is extremely stable under practical operating conditions, such as permanently increased ambient temperatures.

A pneumatic actuator equipped with such a safety device is presented in the sectional drawing below.

Summary

The safety equipment detailed here are simple systems, enabling the pneumatic control valve to maintain, or to reverse, the fail-safe position upon outbreak of fire. Pneumatic control valves could now be used in fields of application not previously considered possible.

Safety Cartridges:

Compared to pneumatic control valves with standard fail-safe action, actuators equipped with these innovative safety devices are able to maintain the fail-safe position over an extended period of time when exposed to fire.

The safety cartridge filled with intumescent material plays an essential role in this safety technique. Thanks to these cartridges, the valve trim remains effective even at the extremely high temperatures of a fire, thus preventing leakage of potentially hazardous media or loss of product. The cartridges compensate for the loss in force of the springs, which under normal conditions guarantee fail-safe action.

Another asset of this system is its cost-effectiveness compared to other safety equipment in use. Since the use of safety cartridges can replace more complex and expensive safety devices or additional fire shut-off valves, they will prove to be another counter to increasing costs.

Reversing Fail safe units:

With this system, conventional fail-safe action can be reversed when a fire breaks out. The release of preloaded and bound spring discs reverses the direction of the standard fail-safe action of pneumatic actuators. An important aspect of this method is the fact that the temperature range at which the springs are released can be pre-selected as needed.

In view of all the advantages of the modern safety equipment developed by SAMSON, the use of pneumatic control valves could now be considered even where sensitive applications are concerned.

Bibliography

1. Schneider, W. 1992. Der Metallbalg, ein zuverlässiges Dichtelement in Stellgeräten. In Chemietechnik, No. 3: 54-60.
2. Schneider, W., and Bartscher, H. 1988. Stellgeräte im Rütteltest. Chemie-Anlagen-Verfahren, No. 8: 84-90.
3. Kiesbauer, J., and H. Hoffmann 1998. Verbesserte Prozeßzuverlässigkeit und Wartung mittels digitaler Stellungsregler. Automatisierungstechnische Praxis, Vol 40, No. 2: 22-34.
4. Vogel, U. 1991. Trends in der Stellgeräteentwicklung. Chemie-Anlagen-Verfahren: 59-62.
5. SAMSON AG. 1994. Stellantrieb mit Sicherheitseinrichtung. Patentschrift DE 42 39 580 C2.
6. DIN 4102, Brandverhalten von Baustoffen und Bauteilen.
7. BSI 6755/2, Testing of valves, Part 2 1987. Specification for fire type-testing requirements.
8. SAMSON AG. 1997. Pneumatisch betätigbare Antriebseinheit. Patentschrift DE 196 49 440 C1.

Fluid Kinetic Energy as a Selection Criteria for Control Valves

Abstract

A selection criteria is provided that assures a control valve will perform its control function without the attendant problems of erosion, vibration, noise and short life. The criteria involves limits on the fluid kinetic energy exiting through the valve throttling area. Use of this criteria has resolved existing valve problems as demonstrated by retrofitting of the internals of many valves and vibration measurements before and after the retrofit. The selection criteria is to limit the valve throttling exit fluid kinetic energy to 70 psi (480 KPa) or less.

Nomentclature

• A_o Valve Throttling Area, in^{2 or m2}
• c Fluid Sonic Velocity, ft/s or m/s
• KE Fluid Kinetic Energy, psi or Kpa
• M1 Units Conversion Factor, Table 1
• M2 Units Conversion Factor, Table 1
• Vo Fluid Velocity at Trim Throttling Area, ft/s or m/s
• w Mass Flow Rate, lb/h or kg/s
• ro Fluid Density at Trim Exit, lb/ft3 or kg/m3

Introduction

For many years the traditional method of sizing and selecting control valves has been to select a valve that contains the design pressure and temperature and meets the maximum capacity requirements. In addition to meeting capacity requirements and serving as a pressure boundary vessel, the valve should perform its intended control function, have long internals (trim) life, provide good shut-off and be relatively maintenance free. There is a need for guidelines to evaluate if a valve and its trim will provide this type of service.

This paper presents a criteria for selecting a valve design capable of eliminating problems. The guideline imposes limits on the kinetic energy of the fluid exiting from the valve trim. The criteria applies to all linear motion valve types. Each type of valve is capable of meeting the kinetic energy criteria for many of the flow conditions that have been dictated by tradition and experience.

Butterfly and Ball valves usually meet the proposed criteria for kinetic energy. The pressure drop across these valves is not large enough to accelerate the flow to a high velocity level. Thus, a much lower value of energy is realized.

Examples are given in which measurements have been made on problem valves and the same measurements made after the valve has been retrofitted with a different trim that limits the kinetic energy exiting from the valve trim. The measurements that are reported are vibration measurements that quantify the effect of the change in the valve trim. The vibration of the valve and the piping system is a strong indicator of valve integrity. It is a direct result of the energy levels in the fluid passing through the valve. As such, it is an indicator of the ability of the valve to provide good control with long life and low maintenance costs.

Valve Selection Process

There are numerous texts that cover the selection of control valves. Two of the most frequently used are ISA (1976) and Driskell (1983). The first step in selecting a control valve is to calculate the required flow capacity, Cv, based upon the requirements of flow rate, inlet and outlet pressure, and the fluid properties. Internationally accepted standards for calculating the required capacity are available in ANSI/ISA (1985) and IEC (1976, 1978, 1980) publications. The required Cv is then compared against tables of valve size and designs provided by the valve manufacturers. The valve hardware is selected to provide enough flow for the given conditions. Many different valve designs will satisfy the capacity requirements and so additional selection guidelines are used to make the final decision. Final selection of the valve and trim type is made through experience and/or by looking at one of the following parameters: pressure drop, pressure drop ratio (pressure drop divided by inlet pressure), fluid velocity or as presented here, the fluid kinetic energy.

Valve designs have ranges for the amount of pressure drop (energy) that they can effectively absorb. For example, low pressure drops are handled by butterfly valves. As the pressure drop level increases, a ball valve would be needed. Still larger pressure drops would require the linear motion globe/angle type valves. The globe/angle designs incorporate many different valve trims depending upon the level of pressure drop starting with a simple plug that opens an orifice. The next range of pressure drops would require a ported cage to help guide the plug and contain the energy dissipation. For the largest pressure drops, a tortuous path trim design is needed. For different valve and trim selections, the acceptable pressure drop ranges overlap. In general, the cost of the selected valve increases with the valve's ability to handle higher pressure drops. Manufacturers have developed designs to extend the pressure drop ranges in order to serve the market with the lowest first cost equipment. This extension of ranges usually is achieved by harder materials that may tolerate the resulting cavitation, erosion, vibration and noise levels.

Driskell (1983) in his chapter titled “Velocity, Vibration, and Noise” discusses the reasons why velocity should be controlled. Excessive velocity causes all of the destructive effects that result in a poor valve application. He notes that velocity induced vibration and noise are “...a blessing in disguise in that they are a warning of impending failure.” Driskell does not discuss where in the valve the velocity needs to be controlled. Unfortunately, when velocity guidelines have been translated to control valve selection they have been interpreted as the velocity exiting the valve body. By the time the fluid is ready to exit the valve body, the influence of “high energy” has already been imprinted into the fluid stream. For example, the fluid velocity exiting the trim may have created high velocity, erosive jets, areas of low pressure with resulting flashing and cavitation damage and noisy shock waves. Velocities should be controlled at the trim outlet, not the valve outlet.

The valve industry has in some cases defined velocity through the trim as a design guideline. These are presented in Ho (1995), Kowalski, et al. (1996), Laing, et al. (1995), Miller (1993, 1996), Stratton and Minoofar (1995) and are used as a basis for the presentation of the criteria discussed in this paper. Schafbush (1993) argues for emphasis on the driving force, pressure drop, instead of the results of the driving force (velocity and kinetic energy) as the selection criteria. Just looking at the pressure drop or fluid velocity at the trim exit ignores the density of the fluid, which is an important parameter in accessing potential problems. A guideline based on the kinetic energy exiting the valve trim involves the driving force, pressure drop, the resultant velocity and the fluid density. Many years of experience in applying this criteria have indicated it is a reliable indicator that is not overly conservative and is applicable to all valve designs.

Trim Outlet Kinetic Energy

For kinetic energy evaluation, the location in the valve of greatest concern is just downstream of where the fluid is throttled or controlled. At this location, the flow area is the smallest and the fluid velocity and kinetic energy are the highest. The parts of the valve responsible for controlling and seating are often located at this point and are therefore subjected to the highest energy fluid.

Figure 1 shows the throttle area for various kinds of valve trim. For a top guided globe valve, the trim outlet flow area is the annulus area between the plug and seat. In a cage guided valve, the trim outlet flow area is the exposed area of the windows in the cage. For a multi-path cage, the trim outlet flow area is the total area of all the exposed flow paths. For multi-stage trims, the flow area from stage to stage must not increase too rapidly or else the throttling will take place across the first stages and the later stages will be ineffective, see Figure 1(e).

In a valve, the disk or plug moves to increase or decrease the area through which flow can pass. For a given set of conditions, a fixed area of the trim is open to flow. Under any significant pressure drop conditions, this area will be considerably less than the inlet or outlet area of the valve. As a result, the fluid passing this point will have much higher velocities and kinetic energy levels than in other valve locations. The only way to increase this flow area without increasing the flow rate, is to increase the resistance of the throttling flow path. The flow conditions define how far the valve is open and the valve’s trim design (flow path resistance) defines how much flow area exists at the trim outlet. Once this area is defined, the continuity equation can be used to calculate the velocity of the fluid at the outlet of the trim.

(1)

Figure 1. Throttling exit area (A_o ) examples for typical valve trim designs

The fluid density and velocity are used to establish the fluid’s kinetic energy.

(2)

For gas or steam, the fluid velocity at the trim outlet may be sonic. If it is, the density of the fluid at the trim outlet must be higher than the outlet density, r_o, in order to pass the given mass flow rate, w. This higher density can be estimated using Equation 1 by substituting the fluid’s sonic velocity, c, for the outlet velocity, Vo, and solving for density. Then, this density and sonic velocity are used in Equation 2 to find the kinetic energy.

Table 1. Numerical Constants for Velocity and Kinetic Energy Equations

Valve Trim Kinetic Energy Criteria

The piping industry has long recognized the need to control the kinetic energy levels in the transport of fluids through a pipe. The industry has created design criteria that limits the fluid velocity in the pipe to acceptable limits. For example, a normal criteria for liquids in pipes is to limit the fluid velocity to a range of 5 to 50 ft/s (1.5 to 15 m/s). Assuming normal water densities, this is equivalent to a kinetic energy of 0.16 to 16 psi (1.1 to 110 KPa). The typical criteria for gases is to keep the fluid Mach number (actual velocity divided by the fluid’s sonic velocity) below 0.15. Assuming saturated steam of 100 to 1000 psi (0.7 to 7 MPa) and a sonic velocity of 1630 ft/s (500 m/s), the kinetic energy is in the range of 1.5 to 15 psi (10 to 100 KPa).

Velocity criteria for liquids are much lower than for gases because liquid densities are much higher, resulting in higher energy levels. While the velocity limits are quite different, the kinetic energy limits are very close to the same.

Table 2 shows criteria for a valve trim’s outlet kinetic energy. The valve trim should be selected to keep the kinetic energy below these levels. The examples that follow support the values shown in the table.

Table 2. Trim Outlet Kinetic Energy Criteria

 

For most conditions, an acceptance criteria of 70 psi (480 KPa) for the trim outlet kinetic energy will lead to a trouble free valve. In some applications, where the service is intermittent (the valve is closed more than 95% of the time) and the fluid is clean (no cavitation, flashing or entrained solids), the acceptance criteria can be increased, but should never be higher than 150 psi (1030 KPa).

In flashing service, liquid droplets are carried by their vapor at much higher velocities. To eliminate the risk of erosion, the acceptance criteria for flashing or potentially cavitating service should be lowered to 40 psi (275 KPa). The same criteria exists for liquids carrying entrained solids.

Special applications may require even more stringent kinetic energy criteria. For example, pressure letdown valves used in pump test loops must be vibration free so that proper evaluation of the pump can be made. These valves are designed with trims that reduce the kinetic energy to less than 11 psi (75 KPa). Gas or steam valves with very low noise requirements may also result in extra low trim outlet kinetic energy requirements.

Retrofit Examples

Table 3 shows a summary of the service conditions, before and after trim style, and the corresponding kinetic energy levels for four valve designs retrofitted with multi-stage trim. Each of these valves was retrofitted because the original valve trim was not allowing good control or there were limitations in the valve’s use due to excessive vibration. In some cases, the valves would cause the system to trip. After repeated attempts to fix the problems and the plant’s need for working valves, the valves were retrofitted with trim designed to reduce the kinetic energy at the trim outlet. The only change made to the valves was to change the internal valve trim and hence, the trim outlet kinetic energy. No changes were made to the valve bodies. Since the bodies were not changed, the fluid velocities exiting the valve bodies were the same before and after the retrofit. In all cases, significant improvements in valve performance were achieved by retrofitting the trim to meet the suggested kinetic energy design criteria.

Table 3. Attributes of Four Valves, Before and After Retrofit

 

For examples 1 and 3, the water outlet pressures were close enough to the water’s vapor pressure to suggest cavitation and two phase flow conditions may exist. Therefore, the acceptance criteria for the trim outlet kinetic energy was the more stringent 40 psi (275 KPa) value for the pressure conditions that could result in vaporization.

Example 1, Residual Heat Removal, arnold, et al. (1996)

The valves were originally top guided, Figure 1(a) control valves without a cage. The valves were retrofit with a tortuous path trim such as shown in Figure 1(g). The kinetic energy on the top guided version is calculated in the annulus area created between the plug and the seat ring. The kinetic energy for the retrofitted trim is at the outlets of each of the disks forming the cage.

A typical reduction of the vibration velocity is shown on Figure 2. The accelerometer that resulted in this maximum output was located on the actuator and measured a direction that was rotational around the centerline of the pipeline. Vibration velocity for the five accelerometers located on each of four valves showed reductions in value that ranged from 49 to 91 percent with even larger reductions occurring on piping components in the system.

The retrofitted valves were able to pass full design flow rates without the accompanying cavitation. All concerns regarding the potential of piping fatigue as a result of the vibration were eliminated.

Figure 2: Residual heat removal

Example 2, Feedwater Regulator, parker, et al. (1994)

The original trim started out as a cage guided trim and was later changed to a drilled hole cage in one of many attempts to salvage the valve design. The retrofit used a tortuous path trim, Figure 1(g), that absorbs the fluid energy inside the trim and has an acceptable exit kinetic energy. The throttling points in the original trim are the cage orifices, Figure 1(b), and the small holes in the drilled hole cage, Figure 1(c), tried later.

The vibration velocity results are shown in Figure 3. The reductions in the vibration are quite dramatic because the vibration levels are not very high to begin with. The comparison of results is made with the drilled hole cage trim as results did not exist with the original cage trim. The reductions resulted in at least a 40 percent reduction in the velocity at the piping frequency of 10 Hertz and essentially an elimination of the vibration at the higher frequencies. Displacement measurements showed reductions of 53 percent and acceleration measurements showed an 86 percent reduction.

All of the problems of vibration, plant trips, and broken stems were resolved by the lower kinetic energy levels at the trim exit. The plant was started up and power escalated to full load for the first time on automatic control as was intended from the inception of the plant design.

Example 3, Core Spray, arnold (1995)

The valves were designed with a top guided plug, Figure 1(a). The trim was retrofitted with the tortuous path trim using the logic of Figure 1(g). The throttling area of the original valve was the annulus area between the plug and the seat ring. The retrofit throttling point was the exit from the disk outlets.

Another change in the system was made in this application. When the retrofitted trim was installed, downstream restricting orifices were removed. Thus, the valve pressure drop was increased to a value equivalent to the original trim and the orifice. This represents a more severe set of conditions for the retrofit trim in controlling any destructive affects due to the higher potential energy that would be converted to kinetic energy across the trim.

The downstream piping system vibration measurements were the most significant changes recorded between the pre and post retrofitted valves. These measurements showed that the pipe displacement dropped from 64 to 92 percent. Pre-retrofit values of displacement were 0.090 inches (2.3 mm) or greater and the largest displacement after the retrofit was 0.020 inches (0.51 mm).

The root cause of the system vibration was cavitation. The post retrofit vibration levels were minor and eliminated any concern regarding the piping system stresses and potential for damage due to fatigue.

Figure 3. Feedwater regulator

Figure 4: Steam dump

Example 4, Steam Dump, persad (1995)

The valve instrumented was a steam valve with a flow to open trim consisting of three concentric cages with drilled holes in each cage. The cages were tightly touching so that there was no axial flow between the cages. Each cage was

slightly offset to create a tortuous path for the pressure letdown. This type of trim is shown in Figure 1(f). The throttling area is the flow area caused by the restriction of the last two cages. The outlet area of the last cage is not the throttling area because there is little pressure letdown associated with the expansion from the overlap orifice. The expansion is too large to have much influence and the jet from the overlap area is the dominate kinetic energy source exiting the trim.

The values reported in this case were a sum of the vibration velocity peaks in the 0 to 500 Hertz range. The results are shown in Figure 4 where the vibration velocity magnitude is plotted as a function of the valve stroke. Values are not available beyond 65 percent of stroke for the original trim as the valve was not operated in this region because of the severity of the vibration.

The reduced trim exit kinetic energy solved the severe vibration problems associated with this steam system.

Other Examples

All of the examples presented above happen to be installed in nuclear plants. However, these are typical control valve applications and are representative of the many applications in different industries that have been experienced. In the past 20 years, over 150 valves ranging in size from 2" to 24" x 36" have been retrofitted to achieve the kinetic energy criteria identified above.

Table 4. Partial List of Retrofit Applications

Applications
Condensate Recirculation	Atmospheric Steam Dump
Aux Pump Recirculation	Turbine Bypass
Recirculation	Reactor Water Cleanup
DA Level Control	Wellhead Choke
Aux Feedwater Regulator	Compressor Recycle
Feedwater Regulator	Compressor Anti-Surge
Reheat Spray	Water Injection
Steam Letdown	Injection Control
Auxiliary Steam	Moisture Separator Reheater
Condenser Steam Dump	Gas to Flare

 

Table 4 is a partial list of applications involved. All of these retrofits arose as a result of a problem with the original installation. In all of the cases, the retrofits were successful in resolving the root cause of the valve problem and the only significant change was the limiting of the fluid kinetic energy exiting the valve trim.

Conclusions

A criteria for the selection of a control valve has been provided which goes beyond the many rules and exceptions being used in the industry. The criteria is a limit on the kinetic energy exiting from the valve trim, defined as the throttling point of the trim. It addresses the energy that contributes to the problems associated with valves. The combination of fluid velocity and density cause:

• unstable forces inside the valve,
• low local pressures that result in cavitation,
• erosion of critical parts,
• shock waves that create unwanted noise, and
• turbulence that results in vibration.

Using the kinetic energy criteria, which has many years of application experience, will eliminate valve problems. It will provide the user with a means to evaluate the different types of valve designs that look as though they will meet the system needs.

The first step is to select the valves that can meet the capacity requirements. Then the valve types are sorted to select the correct valve by using the kinetic energy levels. This will assure the engineer that the lowest cost system is installed.

Acknowledgements

We wish to thank the utilities that shared their vibration measurements so that the retrofitted valve benefits could be quantified. Dr. S. V. Sherikar is also acknowledged for his arranging, collection and analyzing the Example 2 data.

References

ANSI/ISA S75.01-1985, Flow Equations for Sizing Control Valves, Instrument Society of America, Research Triangle Park, NC.

Arnold, J. R., 1995, “Private Communication,” Commonwealth Edison Company, January and June.

Arnold, J. R., Miller, H. L., Katz, R. E. , 1996, “Multi-stage Valve Trim Retrofits Eliminate Damaging Vibration,” Power - Gen 96 International, Orlando, Dec. 4 - 6, Penn Well Conferences and Exhibitions, Houston, Book IV pp. 102 - 119.

Driskell, L. R. , 1983, Control Valve Selection and Sizing, Instrument Society of America, Research Triangle Park, NC.

Kowalski, R. A., Mueller, T. J., Ng, K. C., Miller, H. L., 1996, “Black Point Gas Pipeline Storage Pressure Letdown Control Valves,” ASME International Pipeline Conference, June 9 - 14, Calgary, Alberta Canada.

Ho, T. R., 1995, “DragÔ Valves give Kuosheng a 24 MW Boost,” Nuclear Engineering International, January.

IEC Standards: Industrial Process Control Valves, International Electrotechnical Commission, Geneva, Switzerland.
534-1 (1976), Part 1: General Considerations
534-2 (1978), Part 2: Flow Capacity. Section One - Sizing Equations for Incompressible Fluid Flow under Installed Conditions.
534-2-2 (1980), Part 2: Flow Capacity. Section Two - Sizing Equations for Compressible Fluid Flow under Installed Conditions.

ISA Handbook of Control Valves, 1976, 2d ed., Hutchinson, J. W., Editor, Instrument Society of America, Research Triangle Park, NC, pp 180-220.

Laing, D. E., Miller, H. L., McCaskill, J. W., 1995, “Redesigned Recycle Valves Abate Compressor Vibration,” Oil and Gas Journal, June 5.

Miller, H. L. , 1993, “Controlling Valve Fluid Velocity,” Intech, Volume 40, Number 5, pp 32-34, Instrument Society of America, Research Triangle Park, NC.

Miller, H. L. , 1996, “Tortuous Path Control Valves for Vibration and Noise Control,” ASME - API Energy Week Conference and Exhibition, Jan 29 - Feb. 2, Houston.

Parker, Q., Avery, K. J., Miller, H. L., Sterud, C. G., 1994, “Retrofitting Feedwater Valves at North Anna Reduces Vibration and Improves Control,” Power Engineering, November, pp. 69 - 71.

Persad, J., 1995, “Private Communication,” Ontario Hydro, July.

Schafbush, P., 1993, “Take Account of Pressure Control to Avoid Control Valve Cavitation,” Power, August, pp. 55-57.

Stratton, L. R. and Minoofar, D., 1995, “Specifying Control Valves for Severe Service Applications,” Instrumentation & Control Systems (I&CS), October.

Getting Optimum Performance through Feedwater Control Valve Modifications

Brian Leimkuehler, P.E.
(Presently at ComEd, LaSalle County Nuclear Station)

Sanjay V. Sherikar, P.E.
CCI
22591 Avenida Empressa
Rancho Santa Margarita, CA 92688

FROM: Sixth EPRI Valve Technology Symposium
July 14-16, 1997
Portland, Maine

Abstract

Good control of the feedwater system is very important for smooth operation at nuclear power plants. The performance of the feedwater control valves, which are the final control elements, is crucial in achieving the desired level of control in the system. Modifications were made to existing feedwater control valves at a 565 MWe BWR nuclear power plant. These modifications were part of an overall system upgrade, resulting in significantly improved controllability of the Feed Water Control system. The characteristics that are critical for best performance from the feedwater control valves are : fluid velocity control at all operating conditions, high rangeability, proper flow characterization, high actuator stiffness and good dynamic response. By analysis, and observed through experience, a properly designed and maintained pneumatic control system can provide the dynamic response and resolution necessary for feedwater control performance.

Introduction

Typical loops for the main working fluid in boiling water reactors (BWR’s) and pressurized water reactors (PWR’s) are shown in Figures 1a and 1b, respectively. While the two types of nuclear power generation are quite different, there are many similarities concerning the control of the feedwater being fed into the steam generator, or reactor. In both types of plants, smaller startup, or bypass, valve is quite common because conventional valves do not have the high rangeability required for feedwater control service. This type of service can lead to oscillating control problems during transfer from the startup valve to the main valves, which may cause plant to trip. In both these systems, maintaining fine level control in the reactor, or steam generator, is essential. Finally, the feedwater control valves are required to have good responsiveness to recover from transients. Thus, the performance of the feedwater control valves is critical to all nuclear plant performances.

In this paper, the original feedwater control valves at a 565 MWe BWR nuclear power plant are described, along with their characteristics and performance. Following are the modifications made to the feedwater control valves to enhance their characteristics and how the changes affected the overall system performance.

Original Feedwater System

This plant had been in operation for about 24 years when the system modifications were initiated. The feedwater control valves in service since the commissioning of this plant are “velocity control” valves with tortuous flow path trim.

Feedwater Control Valves

A typical configuration of a velocity control valve is shown in Figure 2. Description and characteristics of this type of valves can be found in previous publications (ref. 1,2 and 3). One of the special features of these types of valves is the trim design in which control of fluid velocities is maintained under all operating flow conditions. This approach practically eliminates cavitation which is likely to occur during startup, or under low flow conditions, when the DP across the valve is significantly higher than normal flow conditions. Essentially, the trim is made up of disks which are multi-stage, multi-path flow controlling elements. Each disk has a tortuous flow path consisting of many right angle turns, each of which provides a discrete pressure-reducing stage. The disk stack formed from these disks forms a multi-path cage as shown in Figure 3.

Since each disk can be unique, the overall flow versus stroke characterization for the valve can be customized for individual applications. In the case of feedwater control valves, fine control is required at low flows and high DP’s and, at full load, with high flow low and DP. In the disk stack such as one shown in Figure 3, this is easily accomplished by incorporating disks with large number of turns for low flow conditions, and by incorporating low number of turns, or no-turns, for the high flow end.

Other significant benefits of controlling fluid velocity at all operating conditions is elimination of excessive vibration, noise, and erosion of the trim and body. These problems are common in valves of conventional designs where trim exit velocities are not controlled.

Characteristics of the Original Control Valves

The trim of the original feedwater control valves was a combination of “velocity control” disk stack with a cage on top. The trim was designed so that the valve would operate under normal conditions within the range of the disk stack; however, to handle transients, the valve could open into the caged area. The Cv versus stroke characteristics of the valve, shown in Figure 4, indicates the abrupt slope changes at the transition from disk stack to the cage.

Additionally, there is a transition zone between the disk stack and the cage area where flow control is unresponsive and creates controller problems to maintain steady flow around the transition zone. When the power plant decided to do a power uprate, a corresponding increase in feed flow was required. This increase in flow caused the valve plugs to control flow in the transition zone of the trim and lead to flow oscillations at full power. As a result, the controllability of feedwater flow was poor. This, in turn, led to fluctuations in reactor level and caused reactor power to be reduced farther below the allowable thermal limits which then causes a reduction in power plant efficiency and power output.

The original valve actuators were 200 sq.in. pneumatic, double-acting piston type with internal springs and equipped with positioner, lockup valves and volume boosters. This type of actuator has been known for their reliability, simplicity and ease of maintenance. However, the large chamber required to accommodate the spring results in limited actuator stiffness. This impacts resolution which, in turn, affects the smallest step change that the valve position, or flowrate, can be achieve.

Enhancing Feedwater System Performance - Control Valve Modifications

This plant undertook multiple changes for enhancing the feedwater control system performance. The major contributors towards improving the feedwater control valve characteristics were improved flow characterization and increasing pneumatic stiffness. Other improvements were in the designs of the plug assembly design, bonnet, yoke, positioner and pneumatic controls. All the upgrades were installed without any changes to the design of the existing valve body.

Cv versus Stroke Characterization

A new “full range” disk stack replaced the original disk stack and cage combination. The new trim has essentially the same overall capacity (Cv) in the full open position as before. However, the new stack was characterized to minimize the rate change between normal and transient areas. Also, the transition zone was eliminated. The characteristics of the valves with new trim is shown in Figure 5.

The disks in the new stack were designed for trim exit velocities under 100 ft/s, as before, to eliminate the potential for cavitation, vibration, noise and other associated problems over the entire range of operating conditions.

Actuator Pneumatic Stiffness

The actuator type was changed to a low-volume actuator while keeping the piston area the same. In this type of actuator, the volume of the air inside the actuator above and below the piston is minimized by removing the internal spring. As a result, the actuator becomes much stiffer.

The governing equations of actuator stiffness, and its relationships to valve resolution are defined below.

Referring to Figure 6, the spring constant (stiffness), K, of pneumatic piston actuator is given by

K = 1.4 *A*{P1/L1 + P2/L2 + Ks} (1)

where, A is area of the piston, P1 and P2 are pressures in the lower and upper chambers of the actuator respectively, L1 and L2 are the equivalent lengths of the air volumes in the lower and upper chamber, and Ks is the stiffness of the internal spring. L1 and L2 are defined by,

L1 = V1/A (2a)

L2 = V2/A (2a)

where, V1 and V2 are the air volumes in the lower and upper chambers of the actuator respectively.

This leads to position resolution, Dx, that the valve can achieve as given by

Dx = {Fs - Fd}/K (3)

Fs and Fd are the sums of static forces and the sums of dynamic forces, respectively, that act on the plug. From Equation (1), actuator pneumatic stiffness can be modified by changing any of the variables. However, in practice, the only parameters that makes the biggest changes are piston area (A) and equivalent lengths (L1 and L2) in the chamber. In this case, the piston area was maintained while changing the actuator length to a low-volume actuator. The stiffness for the original actuator and the new actuator are shown in Figure 7. The high values of stiffness that can be achieved show that a properly designed pneumatic actuator is capable of fine resolution control, as in applications for feedwater control valves.

Figure 8 shows typical resolution for the new low-volume actuators when compared with the original actuators, based on Equation (3). Note that the resolution indicated is the capability of the valve and the actuator combination only; in practice, the sensitivity of the positioner and other control elements providing signal to the valve also affect the resolution.

Rangeability

The rangeability of the feedwater control valves is the ratio of the maximum Cv to minimum controllable Cv. The rangeability with the new trim is 170:1 which is comparable to that for the old trim. Such high rangeability allows for a better overlap between the startup valve and the main feedwater control valves during transitions between the two valves.

Other Modifications

A new standard designs for plug assembly, bonnet and yoke significantly improved structural rigidity in the feed water control valves. A new packing configuration consisting of 8 rings of larger OD replacing the original set of 33 rings, eliminated packing leaks during plant shutdown. In addition, the old positioner was replaced by a new type of positioner with simplified controls which resulted in lower maintenance and no drifting.

Results

Since the installation of the upgrades to the original valves, the system operation has improved significantly. The overall enhanced performance is a result of modifications to the feedwater control valves, actuators and controls. The gains in performance due to the actuator upgrades alone are indicated by the reduction in vessel level oscillations, from about 2” peak-to-peak to 1” peak-to peak, and reduction in feed pump discharge pressure oscillations (Figures 9 and 10). During a refueling outage, the valve trim was upgraded and the control system was modified; this resulted in additional oscillation reduction in reactor level, down to about 0.5” peak-to-peak, feed water flow, and eliminated all of the differential pressures between the two feed pump discharges (Figures 10 and 11).

As shown in Figure 8, the resolution of the actuators at full load is significantly better when compared to what was achievable before. In operation, overall resolution of 0.62% was noted. This level of accuracy in positioning allows for fine control of the water level in the reactor.

With the smoothing out of the disk stack characterization, elimination of abrupt flow regions and transient zone have resulted in stable control over the entire range of the valve operations.

The plant has reported “nearly straight-line control” of reactor level, as desired and has practically eliminated all power fluctuations. This allows operation closer to the allowable thermal limit and a small corresponding increase in power.

These results stated above are consistent with the experiences at number of other nuclear power plants, including pressurized water reactors (PWR’s). In each of the cases, proper rules of fluid velocity control, flow versus stroke characterization, high rangeability and stiff pneumatic actuation systems have eliminated feedwater control valve problems.

The new packing configuration has improved reliability in terms of preventing leakage especially during shutdown conditions. Ease of calibration and practical elimination of drift are two benefits realized from the positioner change. Finally, the modifications of pneumatic controls improved dynamic response of the valve enabling it to better respond to transients.

Conclusions

Improving the control valve characteristics significantly enhanced the feedwater system performance. The significant improvements in valve performance were achieved by modifying the valve flow characterization, increasing the actuator pneumatic stiffness, and by understanding and maintaining the actuator system.

The feedwater control valves are reported to operate quietly over the entire range and with considerable less vibration than before. This is attributed to the controlling of trim exit velocities below 100 ft/s, and increased actuator components rigidity.

A properly designed feedwater control valve, with high rangeability, allows for a better overlap between the startup valve and the main feed water control valves during transitions between the two valves. In some cases, use of the startup valve may not be required if the rangeability of the main feed water control valves is adequate.

As proven by this utility, a properly designed and maintained pneumatic controlled feed water valve system can meet the requirements of providing the resolution and responsiveness needed to maximize power plant efficiency and minimize operational problems.

References

1. Brailey, E.J. and Miller, H.L. High Differential Pressure Control Valves to Limit Temperature Swings. Power Engineering, April 1991, pp. 47-50. [industry magazine]
2. Miller, H.L. Controlling Valve Velocity. INTECH/Instrument Society of America, Research Triangle, NC, May 1993, pp. 22-24. [ISA magazine]
3. Rahmeyer, W.J., Miller, H.L., and Sherikar, S.V., Cavitation Testing Results for a Tortuous Path Control Valve. ASME FED-Volume 210, Cavitation and Multiphase Flow, 1995, pp. 64-67. [Conference proceedings]

Specialist Oil and Gas Valves

Go to Subject Titles:- Oil and Gas Cryogenic Ball, Gate, Globe and Check Valves | Oil and Gas General Service Valves | Oil and Gas High Pressure Valves | Oil and Gas High Integrity Valves for Critical Applications | Ball Valve Single Isolation and Double Block and Bleed | Zero Stem Leak Valves | Anderson Greenwood | Primary Isolation Double Block and Bleed Valves |

Prochem Specialist Valving Solutions - Speciality valves are all manufactured from bar or forgings in BSM's state-of-the-art production facilities. With the newest equipment BSM can guarantee the highest quality and the shortest of lead times.

 

Oil and Gas Cryogenic Ball, Gate, Globe and Check Valves

Cryogenic Service Ball Valve

Cryogenic Service Gate Valve

Cryogenic Service Globe Valve

Cryogenic Service Check Valve

Cryogenic Valves for LNG and LPG Applications - Cryogenic valves are used extensively in LNG and LPG terminals and Marine Tankers. Applications include LNG and LPG production trains, gas chambers, transportation pipelines, liquefaction, carrier vessels, FPSO’s, regasification terminals, peak saving plants, storage tanks etc.

 

Oil and Gas General Service Valves

General Service Ball Valve

 

Oil and Gas High Pressure Valves

Jacketed Gate Valves

Pressure Seal Bonnet Gate Valves

Bolted Bonnet Gate Valves

 

Oil and Gas High Integrity Valves for Critical Applications

Prochem Specialist Valving Solutions - World leading onshore and offshore valve applications are detailed in this technical overview.

 

Ball Valves Single Isolation and Double Block and Bleed

Gate Valves

Needle Valves - Single Operation and Double Block and Bleed

Check Valves - Swing and In-Line Piston

PACSON Heads for Deep Water - These high integrity flow control solutions, which unite quality engineering with robust, long-life performance, are seen as the valves of choice for demanding subsea applications the world over. The Pacson name could soon be equally familiar to specifiers of topside, chemical and power generation valves too - from Valve World.

 

Zero Stem Leak Valves

Habonium Valves, Actuators and Accessories - This Oil and Gas Bulletin from Prochem Stainless Steel Specialists includes: Three Piece Valves, Flanged Valves, High Pressure Valves, Cryogenic Valves, Metal Seat Valves, 3, 4 and 5 Way Valves, Special Valves to Eliminate Fugitive Emissions, Spring Return Hand Valves, A Locking Device for Valves, Special Tailor Made Valves, Double Block and Bleed Valves, Compact Actuators and ProfiX Control Valves.

Dedicated Petrochemical Solutions for Valves and Actuators - The process of refining crude oil into petrochemicals involves handling abrasive materials at extreme temperatures and high pressure, whilst adhering to stringent safety and quality requirements at every stage of the process, from refining to distribution. Habonim’s tough metal seated ball valves (MTM) are specifically designed to operate under the severe conditions of the fractional distillation, hydro-cracking and treatment processes. Habonim has been granted certification by SIRA covering automated packages intended to work in a SIL2/SIL3, which demands the highest levels of reliability.

LNG Solutions for Valves, Actuators and Specials - LNG (Liquefied Natural Gas) production involves handling rough, unrefined materials in harsh conditions while adhering to strict safety and quality requirements. From coping with contaminants and high pressure during extraction of the raw gas from deep beneath the earth’s surface, to converting gas at extreme temperatures, Habonim valves provide high quality, durable and reliable solutions to the challenges inherent in LNG processing.

LNG Case Studies - These Case studies detail a range of LNG Cryogenic Valve Applications.

Petrochemical Industry Case Studies - These Case studies detail a range of Petrochemical Valve Applications.

 

 

Primary Isolation Double Block and Bleed Valves

Primary Isolation Double Block and Bleed Valves - Primary isolation double block and bleed valves meet both instrument and piping engineer's specifications, offering significant savings on space, weight, installation and cost. Suitable for line isolation, sample connectors and chemical injection service.

Technical Reference on Primary Isolation Valves - This comprehensive Technical reference from Anderson and Greenwood gives excellent information on:

• Primary Isolation Valve - Primary Isolation Valve applications, advantages and disadvantages, features and benefits, Quarter Turn Ball Valve specifications, OS&Y Needle Type Globe Valve Specifications, HD Needle Type Globe Valve Specifications, along with a comparison with more traditional valve hookups.
• Double Block and Bleed Valves - These valves are integrally forged, one-piece double block and bleed assemblies for primary isolation of pressure take-offs, where the valve is directly mounted to the vessel or process pipe. Instruments may be directly mounted to the valve outlet or alternatively remotely mounted with gauge lines/impulse pipe work. .
• Unique Series of Optional End Connections - This bulletin feature a unique series of really smart optional end connections which can be bolted onto the valve outlet in place of the standard 1/2-inch NPT female threaded connection. Bolt on connections are available as: Instrument Kidney Flange / Welded Connection / Dual Threaded Connection.
• Enhanced Locking Security of Instrument Valves - Ball valve locking handle provides additional security against tampering or accidental loosening as a result of vibration or physical damage. Allows the valve to be locked open or closed.
• Quill for chemical injection and sampling service - designed to ensure high pressure media can be injected into the optimum position of the flow stream through the process pipe work. It also enables clean product samples to be removed from the main flow. Includes details on Sour Gas Materials, Integral Check Valves and Low Temperature service versions.
• Monoflanges - also see ICEweb's Monoflange and Instrument Manifold page.
• Root Valves - An integrally forged one-piece block and bleed assembly for primary isolation of pressure take-offs, where the valve is either screwed or welded directly into the vessel or process pipe without the need for a flanged connection. Instruments may be directly mounted to the valve outlet or alternatively remotely mounted with gauge lines/impulse pipe work.

Installation, Operation and Maintenance of Monoflanges - Comprehensive Information from Anderson and Greenwood.

Close Coupled Monoflanges - This design incorporates all the integrity features of the convention models, however adds even more safety and cost saving features. The design eliminates the requirement for instrument tube, fittings and threaded connections. Mono Flange Direct, can be provided in a direct mount version or a interface mounting plate can be facilitated if required.

“Close Coupled” Manifold and Isolation Valve Mounting System for Direct Mounting DP Transmitters - These systems overcome the problem associated with traditional impulse line connects on transmitter/manifold installations. Remote mounted DP transmitter/manifold installations with impulse lines were first used over 50 years ago to allow technician’s access to transmitters that required regular calibration and continuous maintenance. With the advent of ‘Smart HART and Fieldbus Technologies’ along with highly accurate, reliable transmitters less maintenance, and longer periods between calibration is required. Hence transmitters can be located right at the impulse points with all the associated advantages of this advanced engineering concept.

Specialist Power Plant Valves

HORA is one of Germany's leading manufacturers of control valves with more than 35 years of experience. This independent company specialises in the design and manufacture of severe service valves in power plants, e.g turbine bypass stations, desuperheaters, pump protection valves and feedwater control valves. The company's minimum flow valves protect centrifugal pumps from potential damage caused by thermal and hydraulic overloads at low load operations. Hora and Powerflo Solutions Pty Ltd offer a whole range of products for use in industry, power plants, as well as electric and pneumatic actuators.

Power Engineering Technologies for the Highest Demands - Power plant operators and plant manufacturers research and develop new processes and technologies for power plants worldwide with efficiencies of more than 50 percent and steam temperatures of more than 700°C. HORA is one of the first manufacturers world-wide to tackle the 700° technology. HORA supplies the control valves for the extreme parameters of 700°C and 350 bar in these power plants. For this purpose, new resilient materials which contain high levels of nickel and chromium are researched and applied. In this way, the plant efficiency can be increased above 50 percent, and the CO2 emissions can be reduced simultaneously by a third: Setting the agenda for safe and efficient energy supply across the globe.

Steam Conditioning Valves - Steam conditioning engineering is of considerable importance in the steam generating and steam consuming industries, e.g. power plants, pulp and paper industries, seawater desalination plants, breweries, refineries etc.. As the name already implies, steam conditioning is the simultaneous change of both temperature and pressure - pressure reducing and de-superheating station (PRDS). A steam conditioning valve replaces the separate arrangement of a pressure reducing valve and a de-superheater. It requires less space and is more cost effective.

Guidelines for Operation of Minimum Flow Control Valves - The design and methods to protect a boiler feed pump is a connection of very complex control systems. The information given here should serve as a basis to avoid mistakes in the selection of the components and of the control systems to be used.

Heavy Duty Control Valve - The Heavy Duty Control Valve is a versatile, modular globe valve designed for severe duties. This type of valve can be utilized to regulate and control the flow of gases, steams or liquids in all industrial applications. It is particularly suitable for the water-steam cycle in high pressure/high temperature power plant applications.

De-Superheater Regulator - A de-superheater is a regulating device for control installations in many fields of industry, providing precise cooling.

Forget Your Problems - This Power Technology Bulletin describes the advantages of the Hora Solution and how problems can be solved by these specialist Power Plant Valves.

HORA Turbine Bypass System - A turbine bypass system permits operation of the boiler independently from the steam turbine during start-up, commissioning, turbine trip (shut down) and load alternations. It gives a higher plant availability and operational flexibility over all different operating conditions. The start-up time under cold, warm and hot conditions is reduced. Keeping the thermal transient in the boiler to a minimum continuous flow through superheater and reheater (maintained tube cooling) must be provided and the pressure during the entire start-up has to be controlled. This article describes how the bypass valve achieves this.

Power Plant Valve Applications

Applications for Specialist Power Valves - This technical bulletin provides some information on the various applications.

Stay Cool when Overheating - Cooling of superheated steam is usually performed by the boiler feed water, which is sprayed directly into the steam pipes by fine nozzles. Sometimes, in the event of extreme condition (excessive temperature), quick transition from high to low temperatures can result in thermal shock at the walls of the cooler. The experts at HORA developed a shock therapy named Cooled Cooler to overcome this problem. It prevents an abrupt cooling process and minimizes the risk of thermal stress at materials and the resulting damage.

More efficiency at 700 degrees Celsius - Increasing efficiency in power plant engineering is a hot topic. This technologically challenging endeavour of increasing conventional steam temperatures of 600°C up to 700°C is the requirement and the goal of the project COMTES700. The abbreviation stands for "Component Test Facility for a 700°C Power Plant". It is sponsored by the European Union and involves HORA as one of the technology partners: The power of innovation from Schloß Holte-Stukenbrock. Raising steam temperature from 600°C to 700°C and achieving thermal efficiencies of over 50% is a major step. Increased efficiency of the power plant can be easily explained with physics. The hotter the steam entering the turbine, the more heat energy the turbine blade can transform into rotational energy and feed into the generator. At the same time, it reduces the quantity of coal per kilowatt of generated electricity and the CO2 emissions. At the present time, coal-fired power plants around the world currently emit about eight billion tons into the atmosphere every year.

Pump Protection with Minimum Flow Control Valves - There are two possible methods to protect a high pressure boiler feed pump from overheating through use of a minimum flow control valve during a low load situation or during starting. They are through on/off control or continuous control. Continuous control is used in case of large power stations that must be often started or stopped, in order to minimize the recirculation of the minimum flow required. This results in a substantial increase in the efficiency and a reduction in operating cost.

Desuperheater - The Desuperheater is a regulating device for control installations in many fields of industry providing precise cooling.

Automatic Pump Recirculation Valve - Automatic pump recirculation valves protect centrifugal pumps from possible damage caused by thermal and hydraulic overloads at low load operations by means of an automatic controlled bypass flow which corresponds with the required minimum flow of the pump.

Steam Cooling - Two shift operation power plants Power stations that were originally designed for base load applications are now increasingly being asked to operate on a two shift, stop/start regime; this is more commonly known in the industry as dual shifting. The multiple start/stops that these stations are now experiencing is in some instances causing an increase of operational issues due to the to the constantly changing process parameters. For example dual shift stations will experience additional thermal stress in the headers, drums, high temperature piping, valves plus the auxiliary equipment leading to additional wear and tear of their systems and component parts. This is due to the more frequent use of the plant at severe service conditions. The consequences of the change in plant operation cannot be ignored. If the plant is not operated correctly or more importantly modified properly to handle these changes the lifetime of the components within the plant will decrease enormously. The changing operational requirements of the plant require that the steam coolers, de-superheater valves, drains, feed water control valves, main steam isolation valves and the turbine quick closing valves are reviewed. These critical pieces of equipment have to be specifically designed to take the new dual shifting process requirements into consideration, once this has been done the operational performance of the plant can be improved and wear and tear of systems and components can be controlled and significantly reduced. Consequently as these pieces of equipment have been specifically designed for the new operating conditions of the station they are no longer a limiting factor to the start up time of the plant. The following paper highlights some of the more common issues found in dual shifting power stations with special regards to steam control - Another paper on the same subject can be found here.

Pressure Reducing De-Superheater Stations (PRDS) - In the energy markets for example, power stations, paper mills, municipal waste incinerators or any steam raising plants, the control of steam is of crucial importance. The main function of a PRDS is to control both the pressure and temperature of the steam. A de-superheater valve is basically a control valve with an integrated spray water steam cooling facility. Every application is different and requires a custom built solution. A standard “off the shelf valve “ is rarely the answer. HORA can produce all types of steam cooling devices and de-superheater stations. Every HORA valve is designed and optimised for the specific application and duty - from Chase.

Industry, Power Plants and Process Technology - Pressure Reducing De-Superheater Stations PRDS Installation Guide.

Servicing Power Plant Valves

Power Plant Valves Servicing - The servicing of these severe service valves requires extensive knowledge of the application along with a highly specialised service and maintenance capability.

Other Power Plant Valve Links

Steam Converting Valves - The conversion of superheated high pressure steam into steam at lower temperatures and pressures is a common practice in process industries. This technology is also used in power stations to utilize the steam energy leaving the turbine for other purposes (e. g. for heating). Some applications use two different valves for the steam conversion process: the first for the reduction of the steam pressure and the second for the control of the cooling water - from Samson Controls.

Pressure Regulators

A Pressure Regulator automatically regulates the flow to maintain pressure in accordance with the amount of demand.

Go to Specific Area of Interest: Pressure Regulator Technical Information | Principal of Operation and Sizing of Pressure Regulators | Pressure Regulator "Droop" | Pilot Operated Regulators | Tank Blanketing Valves | Vacuum Regulators and Breakers |

 

Pressure Regulator Technical Information

The following information is from GO Regulator:

Regulator Technical Reference - This Technical reference details Mass Spectrometer Helium Leak Certification, Subatomic Units of Measure, Flow Calculations for GO Regulator Products, CGA Connection Chart, Typical Pressure Regulator along with Applications.

Regulator Glossary of Regulator Terms - A useful reference

Instructions for the General Use of Go Products - Some very useful technical instructions.

Go Regulator Pressure Animations - These Animations give a good indication of how regulators work.

GO Regulator Corrosion Chart

Calculators - A series of Cv, Maximum Flow and Backpressure Calculators from Go Regulators:

• Maximum Flow Calculator for Gases
• Minimum Cv Calculator for Gases
• Maximum Flow Calculator for Liquids
• Minimum Cv Calculator for Liquids
• Back Pressure Maximum Flow Calculator for Gases
• Back Pressure Minimum Cv Calculator for Gases
• Back Pressure Maximum Flow Calculator for Liquids
• Back Pressure Minimum Cv Calculator for Liquids

PSI Conversion Factors

Temperature Conversion Calculator

 

Principal of Operation and Sizing of Pressure Regulators

Cutting Costs using Self-Operated Regulators - Wolfgang Hesse - At the beginning of the last century, the first self-operated regulators were used for simple control tasks which marked the beginning of process automation. Nowadays, many of us are not aware of the advantages, the design, the principle of operation as well as the limits of this type of technology. In this paper, Samson’s Mr Wolfgang Hesse outlines how cost effective self-operated regulators can be. This is a zipped file thanks Samson Controls.
Introduction to Self-operated Regulators - Self-operated regulators take over all the tasks required in a control loop. They integrate measuring sensor, controller as well as control element all in one system (Fig. 2). The combination of these components results in very rugged and reasonably priced devices - Thanks to Samson Controls.

The following links are from Emerson Process Management:

• Introduction to Regulators - Instrument engineers agree that the simpler a system is the better it is, as long as it provides adequate control. In general, regulators are simpler devices than control valves. Regulators are self-contained, direct-operated control devices which use energy from the controlled system to operate whereas control valves require external power sources, transmitting instruments, and control instruments. This comprehensive Technical Reference guide includes articles covering regulator theory, sizing, selection, overpressure protection, and other topics relating to regulators. This section begins with the basic theory of a regulator and ends with conversion tables and other informative charts.
• Glossary - Glossary of regulator terms for reference.
• Principles of Operations & Regulator Sizing Theory - Regulators provide a means of controlling the flow of a gas or other fluid supply to downstream processes or customers. An ideal regulator would supply downstream demand while keeping downstream pressure constant; however, the mechanics of direct-operated regulator construction are such that there will always be some deviation (droop or offset) in downstream pressure.
• Valve Sizing (Standardised Method) - Fisher^® regulators and valves have traditionally been sized using equations derived by the company. There are now standardized calculations that are becoming accepted world wide. Some product literature continues to demonstrate the traditional method, but the trend is to adopt the standardized method.
• Complete Technical Section on Pressure Relief Valves - This huge 10 Meg file is a Download of the complete Technical Section tabbed with bookmarks.
• Temperature Considerations - Freezing has been a problem since the birth of the gas industry. This problem will likely continue, but there are ways to minimize the effects of the phenomenon.
• Sulphide Stress Cracking - NACE MR0175, “Sulfide Stress Corrosion Cracking Resistant Metallic Materials for Oil Field Equipment” is widely used throughout the world. In late 2003, it became NACE MR0175/ISO 15156, “Petroleum and Natural Gas Industries - Materials for Use in H2S-Containing Environments in Oil and Gas Production”. These standards specify the proper materials, heat treat conditions and strength levels required to provide good service life in sour gas and oil environments.

Reference - This section contains information regarding elastomers, metals, regulator tips, conversions, equivalents, and physical data.

The following papers are from CEESI, whilst they are older they still address the fundamentals:

• Operation and Maintenance of Regulators - Jim Massey - the operation and maintenance of regulators is extremely important because a gas regulator is the most critcal mechanism for controlling the movement or ther flow of gas.
• Fundamental Principles of Self Operated Regulators - James Thomson - This paper discusses the basic purpose of regulators, what affects their performance, things to consider when sizing a regulator and capacity calculations for safety devices.
• Causes and Cures of Regulator Instability - William H. Eamey - This paper addresses the gas pressure reducing regulator installation and the issue of erratic control of the downstream pressure. A gas pressure reducing regulator’s job is to manipulate flow in order to control pressure. When downstream pressure is not properly controlled the terra unstable control is applied.
• Gas Service Regulators Installation, Selection, And Operation - Robert McCaslin - Of the many varieties of gas pressure regulators the service regulator is one of the most basic and widely used types. They are typically found on residences, small businesses, and apartments. They are often the final stage of pressure reduction before residential meters, and they typically reduce pounds per square inch inlet pressure to inches water column pressure.
• Fundamental Principles Of Pilot-Operated Regulators - Brent E. Sayer - A regulator is a mechanism for controlling or governing the movement of machines or the flow of liquids and gases, in order to meet a standard.
• High Pressure Regulators - Brent E. Sayer - A regulator may be described as a "mechanism for controlling or governing the movement of machines or the flow of liquids and gases, in order to meet a standard." The primary function of a gas or liquid regulator is to match the supply of the fluid moving through it to the demand for the fluid downstream. To accomplish this, the regulator continuously measures the downstream pressure and makes adjustments accordingly.
• Also there are a huge "swag" of Pressure Regulator papers on the excellent CEESI website, just go to their technical page and type in "Pilot Operated Regulator" on their search engine.

Pressure Reducing Regulator Flow Curves - Selecting a regulator for an application first requires review of its performance capabilities and their alignment with the application’s requirements. The best starting point is the regulator’s flow curve provided by the manufacturer, because it illustrates the regulator’s range of capabilities at one glance. The curve represents the range of pressures that a regulator will maintain given certain flow rates in a system. This technical bulletin provides an overview of how to read regulator flow curves for pressure-reducing regulators. It describes some of the complexities, including droop, seatload drop or lockup, choked flow, hysteresis, and supply pressure effect (SPE), also known as dependency - from Swagelok.

Pressure Regulator Selection Strategy - Using Flow Curves for Effective Regulator Specification - Bill Menz - The best way to select a regulator for your application is to examine its flow curve, which is often provided by the manufacturer. "Flow curve" is a misleading name. You could easily call it a "pressure curve" instead, since a regulator controls pressure, not flow. The curve represents the range of pressures that a regulator will maintain given certain flowrates in a system. When selecting a regulator, you are not just looking for the right size - you're looking for a set of capabilities, which is a function of the regulator's design. A flow curve illustrates the regulator's range of capabilities at a glance - from Swagelok.

Pressure Regulators Simplicity May Suffice - Seeking a good, economical alternative to control valves? Pressure regulators may be the right choice - Pressure regulators are very simple control devices, taking necessary operating energy from the process. In contrast, control valves require transmitters, controllers, and external energy sources - From Dave Harrold and Control Engineering.

 

Pressure Regulator "Droop"

Combating Droop in Self-Contained Pressure Regulators - Tim Gainer - When qualifying valves for any pressure reduction application, there are several factors to consider. Initially, you must decide whether the application requires a control valve in order to be effective, or would a self-contained or piloted regulator be sufficient? from Jordanvalve.com

Dealing with Droop - Maintaining the Set Point in Self-Contained Pressure Regulators - T. Gainer - When qualifying valves for a pressure-reduction application, chemical plant engineers must consider several factors. Initially, they must determine whether or not the application requires a control valve to be effective. Would a self-contained or piloted regulator be sufficient? To make this decision, plant personnel should consider (a) The pressure drop, or the difference between P1 and P2, (b) The set point, (c) The potential for large flow variations and (d) the level of importance of regulation/control. If it meets the design criteria, a regulator will prove a more effective means of pressure reduction in almost all cases. In addition to lower overall costs, a regulator offers other advantages, most important of which is fast response - from Chemical Processing.

 

Pilot Operated Regulators

Fundamental Principles of Pilot Operated Regulators - Steve Berry - For all practical purposes, regulators, used by the gas distribution industry can be placed in either of two categories: Self-Operated or Pilot-Operated. This paper examines them both. Thanks to Emerson Process Management and www.ceesi.com.

 

Tank Blanketing Valves

Tank Blanketing Regulators for Effective Gas Blanketing - Over many years, gas blanketing has become a widely accepted practice in many industries. The process of gas blanketing is simply to create and maintain a slightly positive pressure in a storage tank, vessel or container with an inert gas - from SA Instrumentation and Control.

The Complete Blanketing and Safety Valve System - This technical bulletin gives a description of blanketing or padding, Blanketing Valve Operation and Performance Characteristics - from Anderson and Greenwood.

The Tank Blanketing Technique - Tank blanketing, also known to as tank padding, is the procedure of smearing a gas to the empty space in a storage tank or container (the term storage container refers to any container that is used to store products, regardless of its size). This technique is used for a variety of reasons and typically involves using a buffer gas to protect products inside the storage container. Some of the benefits of blanketing include a longer life of the product in the container, reduced hazards, and longer equipment life - from cheresources.com.

Tank Blanketing Basics Covered - Tank blanketing, or padding, refers to applying a cover of gas over the surface of a stores commodity; usually a liquid. Its purpose is either to protect or contain the stored product or prevent it from harming personnel, equipment, or the environment. In most cases the blanketing gas is nitrogen, although other gases may be used. Blanketing may prevent liquid from vaporizing into the atmosphere. It can maintain the atmosphere above a flammable or combustible liquid to reduce ignition potential. It can make up the volume caused by cooling of the tank contents, preventing vacuum and the ingress of atmospheric air. Blanketing can simply prevent oxidation or contamination of the product by reducing its exposure to atmospheric air. It can also reduce the moisture content. Gas such as nitrogen is supplied in a very pure and dry state - from cheresources.com.

 

Vacuum Regulators and Breakers

Vacuum Control - Vacuum regulators and vacuum breakers are widely used in process plants. Conventional regulators and relief valves might be suitable for vacuum service if applied correctly - from Emerson Process Management.

Pressure Safety Relief Valves

Safety and Relief Valves for Steam, Gas, Vapour & Liquid Service - Protection of personnel and equipment is the paramount concern in the selection of safety relief valves for plant operating systems. Only the most reliable safety valves should be considered for such a crucial role. 

Go to PSV Engineering Headers that interest you by clicking on the hyperlinks: Technical Data | Sizing and Selection | Two Phase Relief Sizing | Safety Relief Valve Design | Codes and Standards | Noise Issues | Safety Issues | Buckling Pin Technology | PSV Replacement, Maintenance, Installation and Inspection | Testing | PSV Monitoring by Wireless | Forums

 

Pressure Safety Relief Valves Technical Data

Pilot Operated Relief Valves - It is a common question asked amongst process engineers on why use a pilot valve for a particular application ? The following article answers this question and provide some insights into the different types of pilot valves available on the market today and their many features and benefits - thanks to Powerflo Solutions Pty Ltd.

General Information on Consolidated Relief Valves - This document covers the Design, Selection, Sizing and More.

Consolidated Safety Relief Valve Maintenance Manual - Whilst predominantly a Maintenance Manual this document does have some very useful technical information including terminology, Pre-Installation and Installation Instructions, Design Features and Nomenclature, Recommended Installation Practices, Maintenance, and Inspection and Setting / Testing.

Anderson and Greenwood Pressure Relief Technical Manual - This 68 page manual from Anderson and Greenwood is fantastic.

Crosby Pressure Relief Valve Engineering Handbook - A 93 page publication-includes fundamentals of relief valve design, terminology, valve sizing and selection - a very handy publication from Crosby.

Pressure Relief Valve Engineering Handbook - Whilst specific for Anderson Greenwood, Crosby and Varec products this manual this document has some useful information. It has been designed to provide reference data and technical recommendations based on over 125 years of pioneering research, development, design, manufacture and application of pressure relief valves. Sufficient data is supplied so that an individual will be able to use this manual as an effective aid to properly size and select pressure relief devices for specific applications. Information covering terminology, standards, codes, basic design, sizing and selection are presented in an easy to use format - from Pentair.

Safety Relief Valve Technical Data - A swag of useful information from Fisher Regulators/Emerson.

Pressure Relief Valve Engineering - The purpose of this amazing resource from Leser Valves is to help understand the “world of safety valves”. Specifically, it explains:

• What is a safety valve
• The applications in which safety valves are used
• How a safety valve is installed
• How to size and select a safety valve
• The global standards and requirements which apply to safety valves

This Technical Engineering Book is intended to be a knowledge resource for the occasional user as well as the advanced user of safety valves. It covers; History and Basic Function, Design Fundamentals, Terminology, Codes and Standards, Function, Setting and Tightness, Installation and Plant Design, Sizing, Selection, Materials, Connections, Quality and Environmental Management, Markings, Approvals, Shipping, Handling and Storage, LESER USPs, Frequently Asked questions and Trouble Shooting. It is a large download but worth it!

Pressure Relief Devices Requirements - The scope of this document applies to manufacture, assembly, selection & sizing, inspections, repairs, servicing, setting & sealing and installation of Pressure Relief Devices in Alberta, Canada. This document covers; Definitions & Acronyms used in this document, Certificate of Authorization Requirements, Overview of The Act, Regulations, Codes And Standards, Scope of Alberta’s Bench Testing Program, Pressure Relief Devices Manufacturing, Assembling, Selection And Sizing, Installation, Operation, In-Service Inspections Requirements and Servicing Intervals, Pressure Relief Devices Design Registration Requirements and Quality Management System Requirements - Whilst being targeted at Alberta Canada this document provides some very useful information - from ABSA.

Safety Relief Valve information - This site is full of excellent information including Introduction to Safety Relief Valves, Types of Safety Valves, Safety Valve Selection, Safety Valve Sizing, Safety Valve Installation, Alternative Plant Protection Devices and Terminology - Spirax Sarco.

Safety Relief Valve Technical Data - Lots of super information here - Safety relief valves are key assets in any process plant that operates under pressure. Acting as a 'last resort', these fully mechanical devices are designed to operate if an over-pressure situation occurs. They therefore safeguard the plant and help guarantee production, but, more importantly, protect the plant's most valuable asset, its workforce. This special interest box has been designed to provide an introduction to safety relief valves. A number of technical papers are provided, giving an overview of basic design types, codes, testing, etc, as well as addressing topical problems such as the influence of back pressures and safety valve noise - from Valve World.

Pressure Relief Design - This resource from cheresources.com has a real "vault" of excellent technical articles including:

• Relief Valve Set Pressures
• Relief Valves: "What Can Go Wrong" Scenarios

Relationship of Design Pressure, Test Pressure & PSV Set Point - William M. Huitt - There have been a number of issues and questions raised over the topic of pipe system leak test pressures, design pressures, and how they relate to the pressure relief device set point pressure. The easiest way to clarify their relationship is to use, as an example, a simplified flow diagram with only the necessary elements included. Using the following simplified flow diagrams this paper will describe the relationship between the pressure relief device, its set point and how and when it affects the design pressure of a piping system, and therefore its leak test pressure - from W.M.Huitt Co.

Pressure Relief "Grace Under Pressure" - Harry J Toups - This presentation is an excellent overview of Pressure Relief terminology, systems, design, code requirements, location of relief systems, choosing relief types, backpressure, Pros and Cons of various types of relief valves and rupture discs, relief event scenarios, sizing of reliefs, typical calcs, chatter, worst case event scenario, Installation, Inspection and Maintenance and typical errors - From the Safety and Chemical Engineering Education Program - from Sache.

Safety Relief Valves Protecting Life and Property - Lester Millard - Generally speaking, safety relief valves have been around since the 1600s in more or less the same design concept. In its primary function, the pressure safety relief valve serves to protect life and property. Acting as a 'last resort', this fully mechanical valve is designed to open based on an over pressure situation within a process pressure system, thus not only protecting life but safeguarding the investment and plant itself. This article reviews the principles of pressure safety relief valves for spring loaded and pilot operated designs. It covers the applicable European and American codes and standards as well as end user procedures that are key elements in establishing safety and safe selection. Testing (set pressure verification) and maintenance - important criteria once the safety valve has been installed and commissioned is also addressed - from Valve World.

Needless Loss of Refrigerant Through Relief Valves During Abnormal Operating Conditions - From Henry Technologies - To prevent nuisance refrigerant loss through pressure relief valves during high ambient or abnormal operating conditions, it is necessary that the relief valve setting be substantially higher than the system operating pressure.

Specifying Surge Relief Valves in Liquid Pipelines - Surge relief valves often last line of protection for a pipeline, saving the day when all else fails, but only if specified and installed correctly - Trilochan Gupta - A pressure surge can consist of multiple events, resulting in up to ten times the normal pipeline pressure. When a surge relief valve opens, it vents the pressure to a safety system. Probably the most infamous example of a relief valve failing is the nuclear accident at Three Mile Island in 1979, but many other incidents have occurred. In 2005, for example, relief valves were partially blamed for the BP Texas City refinery explosion. In that case, the relief valves opened properly, but they caused a flammable liquid geyser from a blowdown stack that was not equipped with a flare. In other words, the relief valves were installed improperly. In 2009, at the Sayano-Shushenskaya hydroelectric plant in Siberia, severe water hammer ruptured a conduit leading to a turbine. A transformer exploded, killing 69 people. It is not known if the plant had surge relief valves, but this is exactly the kind of problem that surge relief valves are designed to solve. To prevent similar problems from occurring in an oil pipeline, proper attention must be paid when specifying and installing surge relief valves - from the ISA and InTech.

 

Pressure Safety Relief Valve Sizing and Selection

Selection and Sizing of Pressure Relief Valves - Randall W. Whitesides - This is an excellent document - The function of a pressure relief valve is to protect pressure vessels, piping systems, and other equipment from pressures exceeding their design pressure by more that a fixed predetermined amount. The permissible amount of overpressure is covered by various codes and is a function of the type of equipment and the conditions causing the overpressure. It is not the purpose of a pressure relief valve to control or regulate the pressure in the vessel or system that the valve protects, and it does not take the place of a control or regulating valve. Proper sizing, selection, manufacture, assembly, test, installation, and maintenance of a pressure relief valve are critical to obtaining maximum protection - from pdhcentre.com.

Valve Sizing & Selection - This link provides valve sizing and selection software programs for Anderson and Greenwood, Crosby, Yarway and Varec- From Tyco Flow Control North America.

Rigorously Size Relief Valves for Supercritical Fluids - Ryan Ouderkirk - Previously published methods can be tricky to apply, and may lead to improperly sized valves. Here is a stepwise, detailed method that more-accurately determines the orifice area. Thanks to Fluor Corp and Clarkson University.

Relief Valve Sizing for Cryogenic Systems - Within a cryogenic system, adequate relief valves must be installed for all vacuum and cryogenic vessels, and also for any cryogenic lines that have the potential to trap cryogenic fluids. Relief valves must be sized so that under worst-case failure conditions, the maximum pressure reached in any vessel is below the maximum safe working pressure (MSWP) for the vessel. No fixed prescription can be given to determine valve sizing for all, or even most cases. Each system must be analysed in detail to properly determine worst-case failure modes and the required relief valve sizing. Such analysis should proceed through several steps, these are detailed in this technical article - from the Physics division of the Argonne National Laboratory.

 

Pressure Safety Relief Valves - Two Phase Relief Sizing

Select the best model for Two-Phase Relief Sizing - Ron Darby and Paul R. Meiller, Texas A&M University Jarad R. Stockton, Ruska Instrument Corp and Clarkson University - A variety of methods exist for sizing valves, but not all give the best predictions for certain conditions. Two-phase flow is frequently encountered in various relief scenarios and there are no data or Red Book coefficients, or even an accepted and verified two-phase flow model that may be used to size valves for such conditions. One reason for this is that two-phase flow is considerably more complex than single-phase, since there is a large number of variables associated with the fluid properties, distribution of the fluid phases, interaction and transformation of the phases, etc. Consequently, there is a variety of models, each of which is based on a specific set of assumptions that may be valid for certain specific conditions, but may not be accurate for others.

Prediction of Two-Phase Choked-Flow through Safety Valves - G Arnulfo, C Bertani and M De Salve - Different models of two-phase choked flow through safety valves are applied in order to evaluate their capabilities of prediction in different thermal-hydraulic conditions. Experimental data available in the literature for two-phase fluid and subcooled liquid upstream the safety valve have been compared with the models predictions. Both flashing flows and nonflashing flows of liquid and incondensable gases have been considered. The present paper shows that for flashing flows good predictions are obtained by using the two-phase valve discharge coefficient defined by Lenzing and multiplying it by the critical flow rate in an ideal nozzle evaluated by either Omega Method or the Homogeneous Non-equilibrium Direct Integration. In case of non-flashing flows of water and air, Leung/Darby formulation of the two-phase valve discharge coefficient together with the Omega Method is more suitable to the prediction of flow rate - from IOP Science.

Proper Relief-Valve Sizing Requires Equation Mastery - JS Kim, HJ Dunsheath, NR Singh - This article is related to the sizing of relief valves for two phase flow.

Sizing of Relief Valves for Two Phase Flow in the Bayer Process - Quoc-Khanh Tran and Melissa Reynolds-Kaiser Engineers Pty Ltd - This paper reviews the methods currently used in engineering design calculations for predicting the relieving capacity of a safety relief valve under various entering flow conditions. The methods considered include the Recommended Practice (RP) 520 of the American Petroleum Institute (API), the Homogeneous Equilibrium Model (HEM) and various published empirical Slip Models. Recent research conducted by the Design Institute for Emergency Relief System (DIERS) has indicated that the API method leads to undersized relief valves in comparison with HEM under certain conditions. Researchers have found that the experimentally observed relief discharge rates are a factor of three times higher than discharge rates predicted by HEM, especially for low pressure fluids. The Slip Models give results close to experimental data, however there are several correlations from which the slip ratio must be carefully selected to obtain appropriately conservative results - from iKnow.

 

Pressure Safety Relief Valve Design

Frequently asked Pressure Relief Valve Questions (from Farris Please note this useful document has been sourced from Webarchive because it is no longer available) including :

• Can pressure relief valves be mounted horizontally?
• How much seat leakage can I expect from a pressure relief valve?
• How often should a pressure relief valve be serviced?
• What are the benefits of soft seat valves versus metal seat designs?
• When must I specify a lifting lever on a Pressure Relief Valve?
• When must I specify the use of a Balanced Bellows pressure relief valve?
• When should I specify a pilot operated relief valve?

Safety Relief Valves Questions and Answers - This document covers some frequently asked questions on Safety Relief Valves - from Instrumentation Tools.

Safety Selector Valve - Dual Pressure Relief Device Systems - Anderson Greenwood developed the patented, Safety Selector Valve in response to the growing demand for cost-effective, dual pressure relief valve and/or rupture disc installations in today’s process industries. The Safety Selector Valve is designed specifically to function as an effective ‘switchover’ device that permits routine or emergency servicing of redundant pressure relief devices with no process interruption, thus providing continuous system overpressure protection.

Reducing Pressure Relief Valve Discharge Noise to Acceptable Levels.

Relief Valve Orifice Sizes - This article details general relief valve information along with orifice sizes. Thanks to controlandinstrumentation.com.

Relief Valves and Vents, How Exit Conditions Affect Hazard Zones - John B. Cornwell, David W. Johnson, and William E. Martinsen - Pressure relief valves and vents in the petrochemical industry are often the last line of defence in averting a major accident. Recent design standards (API 520/521) have been developed which have reduced the recommended exit velocities for hydrocarbons from pressurized storage. There are computer models available which predict the release and dispersion of high velocity gas jets. In some instances, these models have been modified to account for the formation and dispersion of aerosol clouds. This paper compares the API recommended practices with actual test data and current model predictions - from Quest Consultants.

Safely Size and Design Relief Headers - It is often desirable to combine the discharges from safety relief valves into common pipe headers. The common headers are piped to a safe location, with provision for collecting liquid relief and treating vapor discharge. This page discusses the design of relief valve discharge manifolds - from chemeng software.

 

Pressure Safety Relief Valves - Codes and Standards

Relief Systems / Vent Systems - This Technical Measures document refers to codes and standards applicable to the design of relief and vent systems - from the UK Health and Safety Executive.

List of Safety Pressure Relief Valve Standards - This list details both the API (American Petroleum Institute) and International EN ISO Standards for Safety Pressure Relief Valves - from Valve World.

 

Pressure Safety Relief Valves - Noise Issues

PSV Noise - Criteria, Limits and Prediction - MDG Randall - The noise engineer has some twenty or so criteria by which to judge noise and reduce its effect. For the general purposes of power and gas plants, petrochemical and pharmaceutical engineering this article considers the most important three. These are acoustic fatigue, risk of hearing damage and reaction from local communities - from Valve World.

Safety Valve Noise; Limits, Reduction and Control - M. D. G. Randall - First a little philosophy - As a contractor's engineer, one wants to have a model or other method of solution in place before one meets a cause for its use. Surely to have "no available model" shows absence of prior thought. Some models will show lack of thought. As examples we might think of: a model inconsistent with known facts or common sense; no data to substantiate the maths; predictions inconsistent with the data. We will all accept that a simple or basic model is better than no model at all, because, as information is gathered, the extra descriptions and data can be used to improve or change the model. In the following discussion the reader will find examples of a simple model, old information, and issues that are not well defined, but with which it is suggested he work at the present time. No apology is made for this. The issue of noise from safety valves does not appear to be well covered in the general literature and by making reference to issues where there is uncertainty, the author hopes that others may be encouraged to add definition or associate numerical results to them - from Valve World.

 

Pressure Safety Relief Valve Safety Issues

Balanced bellows pressure relief valves - problems arising from modification of the bonnet vent - The UK Health and Safety Executive.

Guidance Manual for Operators of Small Natural Gas Systems (Chapter Two - Regulator and Relief Devices) - From the office of Pipeline Safety.

Safety Engineering Technology Course - This is a really excellent power point presentation which shows examples of mistakes that can be made - From the Materials Processing Research Institute.

Transient Analyses In Relief Systems - Dirk Deboer, Brady Haneman and Quoc-Khanh - Analysis of pressure relief systems are concerned with transient process disturbances that potentially cause overpressure of piping and mechanical equipment. This paper focuses on the application of transient process analyses on the high pressure leach (or Digestion) area of alumina refineries. The impact of vessel blockages and plant power failures are discussed with emphasis on analysis methodology for power failures. Thanks to Hatch.

Back-Pressure Effects on Safety Valves Operating with Compressible Flow - Vincenzo Dossena - The effects of back-pressures on safety valves is a potentially serious problem. Superimposed or built-up back pressure strongly affects the operational characteristics and flow capacity of safety valves. It is common knowledge that this feature is connected to a reduction in the disc lift and/or to the establishment of a subsonic flow regime. Laboratory tests on five different commercial safety valves, especially ordered for the purpose of operating under back-pressure conditions, show a difference between the performance guaranteed by the manufacturer and the actual valve performance. This difference may be so great that the protected equipment might operate over the maximum allowable pressure - from Valve World.

Vibration and Chattering of Conventional Safety Relief Valve under Built Up Back Pressure - S. Chabane, S. Plumejault, D. Pierrat and A. Couzinet - Safety relief valves are devices designed to open when the pressure in the process to be protected exceeds the design pressure. However, in industrial practice, it often happens that the outlet of these valves are canalized through discharge lines which can be different from atmospheric, then there is a built up pressure generated by the flow in the piping which is superimposed to the back pressure in the discharge system. As a consequence, the initial sizing and selection of the safety relief valves, using results from tests conducted under conditions without back pressure are not necessarily valid - from Cetim.

 

Pressure Safety Relief Valve - Buckling Pin Technology

Buckling Pin Technology - From PlantServices.com - The rupture pin and buckling pin valve are self-contained, self-actuating valves for dependable pressure relief or emergency shutdown at accurately predetermined setpoints. A slender, round pin- the buckling pin- restrains a bubble-tight piston or plunger on a seat. Low-tolerance inserts hold the pin at both ends. Too much axial force from system pressure acting on the piston or plunger buckles the pin. Once the pin is bent, subsequent valve action is full and rapid.

 

Pressure Safety Relief - Rupture Discs

ICEweb has a comprehensive Rupture Disc Page.

 

Pressure Safety Relief Valves - High Integrity Pressure Protection Systems (HIPPS)

Pressure Safety Relief Valves and HIPPS systems - ICEweb's very comprensive HIPPS page.

 

Pressure Safety Relief Valves - Replacement, Maintenance, Installation and Inspection

Safety Relief Valves Replacement, Maintenance, Installation Recommendations - From Henry Technologies - Safety relief valves are relatively maintenance free devices. Even so, we would recommend a periodic inspection of these devices every 6-12 months. A visual inspection should be made to verify the condition of the valves.

Pressure Safety Valve Inspection - This Pressure Safety Valve Inspection article provides information about inspection of pressure safety valve and pressure safety valve testing in a manufacturing shop as well as in operational plants - from Inspection for Industry.

NBIC Pressure Relief Device (PRD) Inspection Guide - This guide provides a basis for NBIC Inspectors use in reviewing Pressure Relief Devices (PRD’s) for compliance with the National Board Inspection Code (NBIC).

What is the Required Frequency of Relief Valve(s) Maintenance? - Bryan Haywood - This is a useful article - from SAFTENG.net.

Pressure Relief Valve Maintenance - This is what you should expect from your repair facility - Alton Cox - Pressurized systems are protected from catastrophe by safety measures including preventive maintenance. The most important piece of equipment in a pressurized system, the pressure relief valve (PRV), is the one piece of hardware that must always be ready to operate properly when needed. However, the PRV also is the one piece of equipment we hope never needs to operate. Because the PRV is the last line of defense against a catastrophic failure of a pressurized system, it must be maintained in “like new” condition if it is to provide the confidence necessary to operate a pressurized system - from Plant Services.

Best Practices in Pressure Relief Valve Maintenance and Repair - Kate Kunkel - Information about maintenance and repair programs for pressure-relief valves. This article covers the various types and functions of PRVs and defining their physical characteristics, Donalson and Simmons along with codes and standards covering PRVs - from Valve Magazine.

Maintenance of Safety Relief Valves - This Technical Resource from LESER provides a collection of documents for repairing or maintaining safety valves. The following topics are covered; Maintenance Fundamentals of safety valves, Repair process, Suggested equipment for assembling, disassembling and rework of critical parts, Disassembly, including sectional drawings, Rework of critical parts including an overview of critical dimensions, Assembly, including options, Spring charts, Testing procedures (set pressure and leak tests), Spare parts lists, Guidelines for inspection, storage and transport and Trouble shooting.

Inspection and Test Plan for Pressure Safety Valve - This is a useful typical Inspection and Test Plan spread sheet - from Inspection for Industry.

 

Pressure Safety Relief Valves Testing

Pressure Safety Relief Valves Testing using incorrect setting methods means your Safety valves may not relieve at the correct pressure! AUSTRAL-POWERFLO’s High Capacity Test Rig is your best guarantee that relief valves will relieve at set point and reseat correctly, without leakage. How Do You Know Your Repairer is Competent? You may not realise that there is much more to achieving safety than just sending your safety and relief valves to any repairer. Austral-Powerflo’s High Capacity Test Rig is designed to simulate conditions close to those occurring in the process. Other methods of setting and testing relief valves, such as nitrogen bottles or air compressor and receiver, do not achieve the same level of accuracy and repeatability. These methods do not simulate a pop action with full lift and, in many cases, only achieve the point of simmer, and may damage your valve. Leaking valves mean energy losses and pollution, increasing your maintenance of ancillary equipment, reducing up-time, which costs you money! The following Table shows results of an evaluation of various commonly used test methods. What method does your repairer use?

Set Point Testing - E. Smith and J. McAleese - Traditional methods of testing Safety Relief valves in BP Amoco group companies conform to the recognised industry standard API 576, and the usual procedure requires that all PSVs are removed from the plant periodically so that their condition can be evaluated in a workshop. Prior tore-installation valves are then "pop" tested on a test bench. On steam boilers the bench set pressure must also be proven in-situ by "floating" the valve. This method is both time consuming and costly. There are, however, methods of testing safety relief valves on line (with and without pressure), notably the Furmanite 'Trevitest" safety valve testing system and comparable in-situ test systems offered by e.g. Crosby and Consolidated. The benefits of these methods are lower costs and, where valves are not "spared", extended plant run times - from Valve World.

 

Pressure Safety Relief Valves - Monitoring by Wireless

Relief Valve Acoustic Monitoring by Wireless - Valve monitoring system can offer operational benefits - Clifford Lewis - The purpose of relief valves are, simply enough, to relieve pressure and provide safe operation. They typically function by opening at a given set pressure, venting, and then resealing after establishing a safe pressure. Very frequently, relief valves see use in gas service where the gas vents to the atmosphere or to a safety flare. These valves are frequently installed in remote locations where monitoring of the valves is difficult. Wireless technology allows for continuous monitoring of these valves without significant capital expense. The non-invasive installation of an acoustic sensor coupled with wireless transmission of data on the relief valve operation provides an easy and inexpensive monitoring solution - from Intech.

Pressure Relief Monitoring Using Wireless Instruments - Wireless sensor networks enable new best practices of pressure relief valve monitoring. In particular, the application of wireless acoustic monitors is very effective for a large component of the installed pressure relief valve population. The same sensors can also detect leakage through isolation and by-pass valves for many service conditions - from Control Microsystems.

 

Pressure Safety Relief Valves - Forums

Safety Relief Valve Engineering (PSV) Technical Support Forum - mutual help system for engineering professionals - From Eng-Tips.com.

Relief Devices Forum - from Cheresources.com.

Rupture Discs

Rupture Disc Technical Information

An Introduction to Rupture Disc Technology - from BS&B.

The following excellent technical references are from Cheresources Philip Leckner:

• Rupture Disks for Process Engineers - Part 1: General
• Rupture Disks for Process Engineers - Part 2: How do we size it?
• Rupture Disks for Process Engineers - Part 3: How Do We Set the Burst Pressure?
• Rupture Discs for Process Engineers - Part 4: Temperature and Back Pressure
• Rupture Disks for Process Engineers - Part 5: The Relief Valve/Rupture Disk Combination
• Rupture Disks for Process Engineers - Part 6: Specifying the Rupture Disk

Getting the Most Out of Your Rupture Disc - For Optimum Rupture Disc Performance, Pay Attention to Installation, Operation and Maintenance - Dean Miller - Rupture disc devices provide overpressure protection for a variety of storage and process vessels and equipment. The objective of the rupture disc is to maintain a leak tight seal and be a passive bystander until called upon to relieve excess pressure. While this is generally the case, there are times when rupture disc performance can be adversely affected through various installation, operation and maintenance practices. This article reviews some of these practices, real-life observed consequences, and corrective or preventative measures that can improve rupture disc performance - from Fike Corporation.

The following technical papers are from oseco:
Rupture Disc Terminology and Concepts - A comprehensive list here.

A Structured Method for Proper Selection of Rupture Disks for Safety Relief in Ammonia Plants - Jeff Scoville and Alan Wilson - Proper selection of a rupture disk is more than performing sizing calculations to make sure it is adequatelysized for the emergency event. Criteria such as operating pressure and temperature, material selection, gasor liquid service, etc. must be evaluated to determine the best disk type for the application. The cost of notevaluating such criteria can be significant to operations if the ammonia plant has excessive “nuisance” failures of an improperly specified rupture disk. This paper will present a structured step-by-step method for determining the appropriate rupture disk type for an application - from Oseco Inc.

The Use of Certified KR for Rupture Disks - Jeff Scoville - The ASME Section VIII, Division 1, 1998 code established a new code symbol stamp forrupture disks in 1999 called “UD”. While the Code recognized rupture disks as acceptable pressure relief devices prior to this revision, there was no formal process for product certification. Very few manufacturers had performed flow testing of their products, therefore the methodologies for sizing relief systems reflected in the ASME Code and API Recommended Practices (RP) were estimates at best. The new UD stamp now requires any product carrying the stamp to be flow tested at an ASME PTC-25 accepted flow laboratory in the presence of a representative from the National Board of Boiler and Pressure Vessel Inspectors. Results of the flow testing are communicated directly to the user via the certified flow resistance factor (KR) and minimum net flow area (MNFA) stamped on the disk tag. These values are also published in the National Board Red Book, which also covers relief valves.

Rupture Disc Specification

Rupture Disc Specification - A simple way of understanding and comparing rupture disk specifications is to recognise the definition given by AS1358 for PERFORMANCE TOLERANCE.

Rupture Disc Questions - A series of questions to ask when specifying a rupture disc - from Fike Corporation.

Rupture Disc Standards

Rupture Disc Australian AS1358 Standard

ASME Code and Rupture Discs - A technical bulletin covering Standards, Terminology, Rupture Disc Performance Requirements, Sizing Methodologies, Manufacturer Certification, Rupture Disc Device Certification,  Rupture Disc Marking Requirements and ASME Application Requirements - from Fike Corporation.

Rupture Disc Sizing

Rupture Disc Sizing - The objective of this bulletin is to provide detailed guidance for sizing rupture discs using standard methodologies found in ASME Section VIII Div. 1, API RP520, and Crane TP-410 - from Fike Corporation.

Bursting Disc Technology - Some useful information from Marston Technologies.

Rupture Disk Preliminary Sizing for Atmospheric Venting - Preliminary sizing for rupture disks on liquid or gas service venting to atmospheric pressure. Imperial (English) units only - from www.cheresources.com

Rupture Disc - Pressure Relief Valve (PRV) Combinations

Best Practices for Rupture Disc (RD) - Pressure Relief Valve (PRV) Combinations - Rupture discs, also known as bursting discs, are commonly used to isolate pressure relief valves from corrosive or otherwise fouling service on the process side and/or the discharge side. This paper will discuss the various code requirements, the practical aspects, and recommended best practices. The basis of most of the discussion comes from ASME Section VIII Division 1; however similar requirements and/or principals are found in API RP520 and EN ISO 4126-3 - from Fike Corporation.

Rupture Disk Specification

Whilst every effort is made to ensure technical accuracy of the information supplied on iceweb.com.au, Keyfleet Pty Ltd and its employees accept no liability for any loss or damage caused by error or omission from the data supplied. Users should make and rely on their own independent inquiries. By accessing the site users accept this condition. Should you note any error/omission or an article offends please do not ignore it, contact the This email address is being protected from spambots. You need JavaScript enabled to view it. and we will review, rectify and remove as necessary.

Provided by POGC Sensor Technology

Performance Tolerance

A simple way of understanding and comparing rupture disk specifications is to recognise the definition given by AS1358-1989 for PERFORMANCE TOLERANCE (section 1, definition 1.2.8, as follows):

“Performance tolerance - a range of pressure in positive and negative quantities or percentages which include both manufacturing range and bursting tolerance at a coincident temperature, which is applied directly to the specified bursting pressure.”

• Section 1, AS1358 is available here.

A rupture disk is usually specified using a MIN-MAX range of pressure at a specified temperature. When a MIN-MAX range is given by the supplier, the other specific details necessary to specify are:

1. The nominal burst pressure

2. The manufacturing range

3. The burst tolerance

In some cases suppliers try to confuse the issue by stating a MIN/MAX but applying it to the manufacturing range only. The above (1-3) should be asked of the supplier to ensure their complete understanding of the true MIN/MAX per AS1358 as the true MIN/MAX incorporates not only the manufacturing range but also all burst tolerances.

The performance tolerance can be shown in the following diagrammatical arrangement.

The inclusion of manufacturing ranges and tolerances in the PERFORMANCE TOLERANCE means that the batch of disks being ordered today and future batches will not burst outside this range at the at the customer’s specified coincident temperature.

The testing that is done in the factory determines the actual burst pressure of the batch. If the customer nominates ASME VIII certification, 2 tests are made in an oven at the customer’s coincident burst pressure. The average of these tests must lie in the manufacturing range and is stamped on the disk tab in accordance with ASME VIII. If ASME certification is needed, then the stamping on the disk tab cannot vary.

If stamping is needed to be MIN/MAX one can specify the same stringent testing as the ASME code by stating that the testing shall include at least 2 tests at the elevated, coincident temperature that fall in the manufacturing range, eg they can then specify in accordance with ISO6718. This is the code that AS1358 has been written around.

Essentially, if you ask for a tighter MIN/MAX, you are asking for a tighter manufacturing range. Manufacturing ranges are specified in the manufacturers’ literature. A zero manufacturing range is the tightest, meaning the average of the burst tests in the factory must equal the nominal burst pressure at the coincident temperature.

The burst tolerance is always ±5% in accordance with all the rupture disk codes for stamped burst pressure equal to or greater than 40 PSIG (275.8 kPag) @ 22 ºC.

The burst tolerance varies, according to the particular disk design for stamped burst pressures below 40 PSIG @ 22 ºC.

The burst tolerance refers to the accuracy of each disk in the batch you have just received.

Essentially, once it has been confirmed what manufacturing range (ask the manufacturer to specify low end and high end) and what burst tolerance applies to the high end and low end of the manufacturing range, then the performance tolerance is worked out. If the supplier cannot provide this detail then they should confirm that all manufacturing ranges and tolerances are included in the MIN/MAX they have given.

Maximum Operating Pressure

Any rupture disk can be operated to whatever pressure one likes. However, at what pressure should one operate to for reliable performance, so that the life of the disk is not reduced? From more than 65 years experience in the field BS&B has established the following operating pressure to burst pressure ratios (expressed as %). Some examples are:

BS&B Types	Description	Operate from Full Vacuum to Y% of the Stamped BP
S90, JRS, CSR, RLS, MRB, ECR	Single Section reverse buckling disk	90%
GFN	Tension loaded disk that is scored after disk crowned	85%
XN, LCN, DV	Composite tension loaded disk	80%
EXP/DV	Tension loaded, domed, composite disk with vacuum support	80% of nominal
AV, AVV	Flat composite disk with gaskets	60% of minimum
BV	Tension loaded, solid metal prebulged disk with vacuum support	70%
MBV	Integral disk & holder of high grade impregnated graphite with vacuum support	80%

Cyclic / Pulsating Duties

The next question is which disks can be operated reliably in cyclic/pulsating duties.

The answers are S90, JRS, RLS, MRB & ECR. All others are tension-loaded disks that will have a limited cycle life but are very good in static conditions. Hence, the operating ratio can be qualified only depending on the type of service that the disk is used in. This optimum value must therefore be seen with caution.

On the specification sheet, the next step is to specify the maximum positive operating pressure that the disk should see, at the coincident burst temperature to ensure maximum service life.

To specify this, for the worst case condition one must establish first, if the low end of the manufacturing range will be:

• 40 PSIG or higher

• Lower than 40 PSIG

Case A - 40 PSIG or Higher

In this case, you may operate to Y% of the stamped burst pressure (at worse case Y% of the minimum of the manufacturing range).

Case B - Lower than 40 PSIG

In this case you may operate to Y% of the MIN. hence the burst tolerance must be deducted from the stamped burst pressure (at worse case the burst tolerance is deducted from the low end of the manufacturing range and the MIN is calculated. Then Y% is applied to the MIN).

The performance of rupture disks at temperatures other than the coincident disk temperature cannot be guaranteed unless the user is prepared to pay for extra testing. Estimates can be given for various disk materials, although these should not be taken for granted.

Section 1: Scope and General
Australian Standard AS1358: Bursting Disks and Bursting Disk Devices

Shutdown (SDV) and Blowdown (BDV) ESD Valves

Go to Specific Subject: Design of Shutdown (SDV) and Blowdown Valves (BDV) Emergency Shutdown Valves (ESV) | Types of Shutdown (SDV) and Blowdown Valves (BDV) | Reduced Bore Valves | Shutdown (SDV) and Blowdown (BDV) Underlying Causes of Failures and Lessons Learnt | Material Selection for Shutdown (SDV) and Blowdown Valves | Shutdown Valves (SDV) and Blowdown Valves (BDV) Seat Leakage Classifications and Standards | Shutdown Valves (SDV) and Blowdown Valves (BDV) Fire Safe Standards | Valve Actuators | Shutdown (SDV) and Blowdown (BDV) Valve Actuator Sizing and Torque Requirements | Valve Shear Torque | Valve Actuator Closed Loop Breathing | Shutdown and Blowdown Valve Applications | Shutdown and Blowdown Valve Maintenance | Partial Closing and Stroke Testing | Riser Emergency Shutdown Valves (RESDV) | Fire Safe Actuators and ESD Valve Fire Shelter | HIPPS Systems

Coming Soon! Professional Certificate of Competency in the Selection, Commissioning and Maintenance of Shutdown, Blowdown, Severe Service and Choke Valves Emergency Shutdown Systems (ESD) are a fundamental part of the safety systems associated with oil and gas, utility and other hazardous processes. Associated with these systems are specific valves which are used to isolate and blowdown the processes. These are referred to as Shutdown (SDV) and Blowdown (BDV) Valves respectively. Under emergency situations it is critical that these valves operate correctly. Thus the engineering of the valves and their associated actuators is paramount in ensuring plant safety. They must meet the Fire Safe and Reliability criteria determined by IEC16508 and IEC16511. This Professional Certificate of Competency (PCC) covers the requirements in detail. In addition, the course addresses Severe Service Valves and Wellhead Choke Valves. Severe Service Valves are required where the process can cause damage to conventional valves through erosion, high noise, cavitation, high vibration, possible mechanical damage to the valve trim, other components and the process equipment around the valve. These valves are generally specialist designs that overcome these issues by "smart" design. Get Further Information.

 

Design of Shutdown (SDV) and Blowdown Valves (BDV) Emergency Shutdown Valves (ESV)

Functional Safety of Globe Valves, Rotary Plug Valves, Ball Valves and Butterfly Valves - This manual is intended to assist planners and operators during the integration of control valves into a safety loop as part of the safety function and to enable them to safely operate control valves. This manual contains information, safety-related characteristics and warnings concerning the functional safety in accordance with IEC 61508 and concerning the application in the process industry in accordance with IEC 61511 - from Samson Controls.

Enhanced Reliability for Final Elements - Dr Thomas Karte - Process valves, sometimes also addressed as final elements are in many cases the most decisive factor when it comes to calculating the SIL level for a safety instrumented function (SIF). Testing procedures like partial stroke testing can provide enhanced diagnostic coverage and therefore help to get improved reliability data for the total loop. Verification of this 'diagnostic data' and proper integration of these procedures into the safety instrumented system (SIS) and basic process control system (BPCS) environment at the same time poses a challenge. New developments on actors and relevant approvals are presented as well as instrumentation with new functionality to support diagnostic coverage, different topologies for connection to SIS and BPCS are discussed - from South African Instrument and Control and Samson Controls.

Emergency Shut Down Valves (ESD) - Quarter-turn valves are the most common ESD control valves for actuation. Automatic control valves are fitted with hydraulic, pneumatic and electric actuators that respond to changes in pressure, flow or temperature, and automatically open or close the valve. Danger and damage from fire at refineries, petrochemical and offshore installations can be minimized by efficient protection of the systems controlling the plant.Remote valve operation station of fire proof actuator with accessories and air reservoir system to guarantee three complete cycle in the event of fire pneumatic operated with “Darchem” fire proof protection - from Samson Controls.

Need for an Industry Standard for ESD valves from an Engineering and Safety Point of View - Meghdut Manna - Tahakum East -Since the Piper Alpha disaster in the North Sea, design of ESD valves has been given top priority and remains to be of great concern for plant safety management. Constant improvements have been made to ensure the integrity of the ESD valves. Essentially, ESD valves should perform their duty (usually closure of valves) under plant demand condition. To meet the production bottom-line, these valves are required to remain open for months, even years, which leads to build up or corrosion in the valve internals. Final control element is the weakest link in the SIS. From the safety users group.

Shutdown Valve - A shut down valve (also referred to as SDV or Emergency shutdown valve, ESV, ESD, or ESDV) is an actuated valve designed to stop the flow of a hazardous fluid or external hydrocarbons (gases) upon the detection of a dangerous event. This provides protection against possible harm to people, equipment or the environment. Shutdown valves form part of a Safety instrumented system - From Wikipedia, the free encyclopedia.

The following References are from Seridium;

• Valves Quick Reference Handbook - This 51 page Engineering reference is a huge repository of technical information on valves, accessories and much more.
• Guidance on Valves Type Selection - B.Ricardo - This excellent Technical Engineering Resource provides information on Required function, Service conditions, Fluid type and condition, Fluid characteristics, Frequency of operation, Isolation requirements, Maintenance requirements, Environmental considerations, Past experience in comparable conditions, Weight and size and Cost.
• Valve Functions and Basic Parts - There are many types, shapes, and sizes of valves, they all have the same basic parts. This technical manual reviews the common parts and functions of a valve.
• Application of Valves - In piping systems, industrial valves play a very crucial role in handling fluids. Different types of Valves are used to meet various applications like on-off, throttling, quick open / close, flow diversions etc…these valves find their applications in industries like refineries, Treatment, Effluent Treatment, Food & Beverages, Pulp & Paper Oil & Gas etc. Selection of right type of valves for a particular application is vital for trouble free service. Details of various types of industrial valves for a particular standards & application areas are included.

Emergency Shutdown - Isolation Valve Requirements - This document has some useful information on Shutdown Valves (SDV).

The Following are from Metso Automation

• ESD Valve Selection Guide - General ESD Valve Definition - This 14 page document is an excellent Reference - Covers SIS Standards, Specifications, Valves, Actuators, Safety Valve Testing, Materials, Fire Protection, Safety Integrity Level (SIL), Total Life Cycle, Applications, Quality Assurance and Terminology.
• The Value of Safety Valves - Juha Yli -Petays - Safety valves are the most important components in the safety loop (sensor, safety logic and final element), because most of the problems that occur are related to the functionality of the final element. It is important to remember that these elements are moving mechanical devices, which operate in very difficult environmental conditions. This makes the need for regular valve testing and for testing while the process is running absolutely essential.
• Bringing Intelligence to On-Off valves and Simplifying On-Off Valve Instrumentation - Juha Kivelä - Traditionally, on-off valves have been instrumented by at least a separate solenoid valve and limit switches. Quite often the desired functionality cannot be achieved by using only a solenoid valve and limit switches, which means that additional pneumatic accessories are needed. For example, if the process requires precise valve opening or closing stroke times, these cannot be guaranteed by using only a solenoid valve; but there is also a need for some extra accessories such as throttle valves.
• Taking Safety Valve Testing to the Next Level - Juha Kivelä - Today’s safety engineers face increasing challenges every day. Safety requirements are becoming more and more demanding, while the global market situation is simultaneously creating constant pressure to reduce costs. The IEC61511 safety standard requirements state that industrial processing plants must determine the Safety Integrity Level (SIL) for all the different areas of the plant. Based on the area SIL classifications, the plants must then be able to dispatch quantifiable proof of compliance with the requirements.

Valve Design Codes - A useful list - from Australian Pipeline Valve.

Introduction to Valve Standards - This Technical Reference provides a useful list of Valve Standards - from OMB Valve Specialists.

The Following Technical Articles are from Emerson Process Management;

• Smart Positioners in Safety Instrumented Systems - Riyaz Ali and LeRoy Jero - A review of the way microprocessor-based digital valve controllers - otherwise “smart positioners” - can improve the capabilities of safety systems in detecting potential risks and heading them off before they become a danger.
• Smart Positioners to Predict Health of ESD Valves - Riyaz Ali and Dr. William Goble - Safety Instrumented Systems (SIS) involve final control elements such as emergency shutdown valves, emergency venting valves, emergency isolation valves, etc. These valves are not continually moving like a typical control valve, but are normally expected to remain static in one position and then reliably operate only when an emergency situation arises. Valves which remain in one position for long periods of time are subject to becoming stuck in that position and may not operate when needed. This could result in a dangerous condition leading to an explosion, fire, and/or a leak of lethal chemicals and gases to the environment.
• Predicting Health of Final Control Element of Safety Instrumented System by Digital Valve Controller - Riyaz Ali - This paper will discuss testing final control element of SIF loop, on-line, while plant is running, by using smart positioners to perform partial stroke test to detect dangerous failures, which would have remain undetected, if testing were not done.

 

Types of Shutdown (SDV) and Blowdown Valves (BDV)

Rotary Plug Valves - This valve construction, simply called “the rotary valve”- summarizes different valve styles under a generic term. All of them have one thing in common: a turning valve shaft for adjustments in valve opening. The form of the obturator varies between a simple drilled-through cylinder and a complicated eccentrically positioned plug with a spherical segment surface. To this category also belong armature types which are described as “cock” valves with a cylindrical or conical plug and a special opening cross-section whose profile is authoritative for the flow characteristics of the valve. The so called cock valve, with tapered plug, has been in use for more than 2000 years and was utilized in earlier days - carved out of wood - to tap wine. With the development of new, high corrosion resistant materials like PTFE or PFA which are frequently used for the lining of inferior metallic valve bodies, these well-known constructions have had a renaissance. This principle is used, however, principally for ON-OFF services and only seldom for continuous control applications - from South African Instrument and Control and Samson Controls.

Valve Style Advantages and Disadvantages - This is a useful spreadsheet - from Samson Controls.

Valve Types - There is a vast abundance of valve types available for implementation into systems. The valves most commonly used in processes are ball valves, butterfly valves, globe valves, and plug valves. This article provides a summary of these four valve types and their relevant applications - from the University of Michigan.

Valve Types and Design - Valves are the most common single piece of equipment found in DOE facilities. Although there are many types, shapes, and sizes of valves, they all have the same basic parts. This comprehensive technical reference provides useful information covering the common parts and functions of a valve - from constructionknowledge.net.

Introduction to Valves - Only the Basics - Valves are mechanical devices that controls the flow and pressure within a system or process. They are essential components of a piping system that conveys liquids, gases, vapors, slurries etc. Different types of valves are available: gate, globe, plug, ball, butterfly, check, diaphragm, pinch, pressure relief, control valves etc. Each of these types has a number of models, each with different features and functional capabilities. Some valves are self-operated while others manually or with an actuator or pneumatic or hydraulic is operated - from World of Piping.

 

Reduced Bore Valves

The following Design Parameters are from Seridium.

Reduced bore or venturi pattern valves should be selected when minimum weight, cost, and operating time are required.

The seat (throat) diameter of reduced bore valves should be selected.

If reduced bore valves are used, the following additional criteria should be satisfied:

• The increased pressure drop is considered in the design of the piping.
• The reduced section modulus is considered in the piping flexibility design.
• Not to be used in horizontal lines which are sloped for continuous draining.
• Drains are installed at all additional low points caused by the installation of reduced bore valves.
• Not to be used in erosive applications such as sandy service, slurries, or fluidized solids without an analysis of the effects of erosion.
• Not to be used in severe fouling, solidifying, or coking services.
• Not to be used in lines specified to be mechanically cleaned or “pigged”.
• Not to be used as block valves associated with pressure relief devices and flare pipe headers.

What is a Full Port or Reduced Port Ball Valve? - These are two different types of ball valves. The major difference between a full bore valve and a reduced bore valve is described here - from Tofine.

Full Bore or Reduced Bore Ball Valves - Full bore ball valve is a valve that the hole diameter of its ball is the same size with the pipe size. Reduced bore ball valves is a valve that the hole diameter of its ball is not the same size with the pipe size. In minimum the reduced ball valves ball diameter are one size lower than the pipe size i.e. 4 inch pipe and ball diameter is 3 inch (usually symbolized as 4 x 3 inch ball valves). From its definition we can quickly know that the full bore will have less pressure drop and reduced bore will have more pressure drop since reduced bore is just like a restriction orifice that narrowing at the middle part. So when full bore or reduced bore ball valves will be used? - from SZ Valves.

What is the Difference between Full Port (Full Bore) and Standard Porting? - This article describes the difference - from Valveman.

 

Shutdown (SDV) and Blowdown (BDV) Underlying Causes of Failures and Lessons Learnt

Assessment of Valve Failures in the Offshore Oil & Gas Sector - John Peters - This comprehensive report describes the findings of an assessment study of data-set information regarding valve problems in the UK Offshore Oil & Gas Industry. It was undertaken by the National Engineering Laboratory, on behalf of the Offshore Division of Health & Safety Executive, as part of a wider initiative to reduce hydrocarbon releases. From the UK HSE.

Emergency Shutdown Valve Study - Industry Operating Experiences and Views:The Way Forward - John Peters - An older study but still very relevant. From the UK HSE.

ESD Valve Failures - This Case Study outlines the criticality of ESD Valves operation and the effects when they fail, It also gives "root causes" and "lessons learnt".

 

Material Selection for Shutdown (SDV) and Blowdown Valves

Control Valve Corrosion Solutions - This document from Emerson Process Management is useful and covers the most common forms of corrosion in valves along with details on NACE standards.

ICEweb's Corrosion Page - Corrosion is a subject that any Instrument Engineer should have knowledge in as selecting the correct equipment and process instruments for a plant is dependant on it. This page provides some excellent technical information about corrosion, forms of corrosion, corrosion effects, how to mitigate corrosion and corrosion monitoring and control. In addition there are Material Selection Guidelines and Corrosion Tables.

ICEweb Control Valve Corrosion Technical Information - This link provides technical information on Valve Corrosion, how it occurs and selection of suitable materials and standards.

 

Shutdown Valves (SDV) and Blowdown Valves (BDV) Seat Leakage Classifications and Standards

Standards for Acceptable Rates of Valve Leakage - This Technical Information covers standards for leakage rates including DIN EN 917 for Thermoplastics valves, BS 6364 for cryogenic valves, along with the three standards used most in the oil and gas, and petrochemical industry API 598, ANSI FCI 70-2 and MSS-SP-61 - from controlandinstrumentation.com.

Zero and Low Seat Leakage Standards and Test Criteria - This very useful technical paper provides information on the standards, an explaination of zero and low leakage test standards and valve leakage classifications - from Global Supply Line.

Valve Leakage - A Lesson in Leakage - All valves leak. Valves may be said to be "bubble tight" or zero leakage; but in actuality that is just a term that specifies the allowable leakage at that classification. There are six seat leakage classifications defined by ANSI/FCI 70-2-1976 (supersedes ANSI B16.104). This article describes the six valve leakage classifications - from The Valve Pipeline.

Introduction to Valves - Leak testing of Valves - Standards for Acceptable Rates of Valve Leakage - Details API standard 598: Valve Inspection and Testing, MSS standard MSS-SP-61: Pressure Testing of Valves and ANSI standard FCI 70-2: Control Valve Seat Leakage - from Wermac.

 

Shutdown Valves (SDV) and Blowdown Valves (BDV) Fire Safe Standards

The most common standards for fire testing of SDV and BDVs are BS6755, EN ISO 10497 and ANSI/API 607.

BS EN ISO 10497 is an International Standard which specifies fire testing requirements and a fire test method for confirming the pressure-containing capability of a valve under pressure during and after the fire test. Comparative Table of BS6755 and EN ISO 10497 - This details the differences - from Meca Inox API STD 607 - Fire Test for Quarter-turn Valves and Valves Equipped with Non metallic Seats, 6th Edition - This International Standard specifies fire type-testing requirements and a fire type-test method for confirming the pressure-containing capability of a valve under pressure during and after the fire test - from TechStreet.

 

Valve Actuators

Valve Actuators - This is ICEweb's Technical Information on Control and Quarter Turn Valve Actuators.

Go to Specific Subject: Compact Valve Actuator Solutions and Systems | Subsea Valve Actuators | Offshore Valve Actuator | High Pressure Manifolds Actuators | Safety Related Systems Valve Actuator Systems | Spring Return Hydraulic Actuators | Spring Return Pneumatic Actuators | Compact Double Block & Bleed (DBB) Valve Actuators | Double Acting Actuator | Compact Actuators in Floating Liquefied Natural Gas (FLNG) Applications | Valve Actuator General Information | Scotch Yoke Design Valve Actuators | Firesafe Actuators | Valve Actuator Standards | Hydraulic Actuator Design and Operation | Electrical Actuator Design and Operation | Control Valve Actuator Design and Operation | Valve Actuator Accessories.

 

Shutdown (SDV) and Blowdown (BDV) Valve Actuator Sizing and Torque Requirements

Correct specification of torque values for Blowdown and Shutdown Valves is absolutely critical to ensure integrity of a facility as the operation of these valves must meet the reliability and availability requirements. The following criteria give a guideline of the requirements, however it must be stressed that any design must meet the Safety and Integrity Level (SIL) defined for the facility. SDV and BDV valves also must be tested and verified in accordance with the facility Safety Case, Failure Modes and Criticality Analysis (FMECA) and Reliability Centred Maintenance (RCM) requirements.

 

Blowdown Valves (BDV) (Normally Open - Spring to Open) Actuator Torques

BDV Valve Start to Open Torque

Actuator Spring Start Torque - A safety factor of 100% (i.e. 2 times) should be applied on top of the valve start to open torque. This is defined as the torque at the 'compressed spring state' at the start of the emergency shutdown blowdown operation.

BDV Valve Reseat Torque (Valve Open Torque)

Actuator Spring End Torque - A safety factor of 25% (i.e. 1.25 times) should be applied on top of the valve opening torque. The spring should provide a torque of 1.25 times the valve open torque at its relaxed fully open emergency shutdown blowdown state.

BDV Valve Running Torque (Resistance Torque)

Actuator Spring Running Torque and Air Running Torque (Minimum Torque Produced by the Actuator) - A safety factor of 50% (i.e. 1.5 times) should be applied and maintained on top of the required valve running torque during the close and open valve running cycles.

BDV Valve Start to Close Torque

Actuator Air Start Torque - Pneumatic operator beginning torque should be 2 times the valve closing breakout torque at the start of the plant blowdown reset.

BDV Valve Reseat Torque (Closing Torque)

Actuator Air End Torque - Pneumatic operator end of stroke torque should be 1.25 times the valve closing torque. This is at the end of the closing stroke (The plant operating BDV Valve closed state).

 

Shutdown Valves (SDV) (Normally Closed-Spring to Close) Actuator Torques

SDV Valve Start to Close Torque

Actuator Spring Start Torque - A safety factor of 100% (i.e. 2 times) should be applied on top of the valve start to close torque. This is defined as the torque at the 'compressed spring state' at the start of the emergency shutdown operation.

SDV Valve Reseat Torque (Valve Closing Torque)

Actuator Spring End Torque - A safety factor of 25% (i.e. 1.25 times) should be applied on top of the valve closing torque. Hence the spring should provide a torque of 1.25 times the valve closing torque at its relaxed fully closed facility emergency shutdown state.

SDV Valve Running Torque (Resistance torque)

Actuator Spring Running Torque and Air Running Torque is the Minimum Torque produced by the Actuator during the closing or opening cycle. A safety factor of 50% (i.e. 1.5 times) should be applied and maintained on top of the required valve running torque during close and open running cycles.

SDV Valve Start to Open Torque (Valve Start to Open Torque)

Actuator Air Start Torque - Pneumatic operator Start to Open torque should be 2 times the valve opening breakout torque at the start of the facility shutdown reset.

SDV Valve Reseat Torque (Valve Opening Torque)

Actuator Air End Torque - Pneumatic operator end of stroke torque should be 1.25 times the valve opening torque at the end of the opening stroke (The facility operating SDV Valve open state.

Proper Actuator Design and Selection Reduces Down Time - Donald Weeks - Covers Valve and Actuator Technology, Torque and Actuator Sizing - from Flowserve.

Trends in Pneumatic Spring Return Valve Actuator Selection - Ian M. Turner - When sizing pneumatic actuators for fail-safe valves, torque safety factors can vary depending on project specifi cations, and valve torques can vary from break to open, running and end to close positions. End-users normally determine the valve safety factor during the design stage and valve manufacturers, therefore, do not need to add extra contingencies. Essentially, these safety margins are determined with the goal that the valve should operate smoothly throughout its service life irrespective of the process condition. Increasingly, the safety factor applied when coupled with the specifi ed minimum sizing and normal supply pressure range for actuator selection, can result in selected actuator output torques exceeding the maximum acceptable stem torque (MAST) specifi ed by the valve manufacturer. In the oil and gas industry, for example, three different application categories for safety margin are commonly defined for on/off actuator valves - from Matic Actuators.

Torque Testing - This Covers: The Importance of Torque Testing and Actuator Selection, The Need for Torque Testing and The Use of Safety Factors When Specifying Actuators - from Geograph Energy.

 

Valve Shear Torque

Maximum Allowable Stem Torque (MAST) - Ball valves(rotary valves) are used as ESDVs/BDVs in critical services like shutdown, isolation and blow down application. Engineers endeavour to ensure reliability and integrity of actuator and its components. However as far as stem components are concerned sometimes either give little attention to mechanical integrity of stem or leave it to valve vendor and assume “Stem design is sufficient enough to withstand actuator torque”. Unfortunately this is always the case, Stems do fail!!! If stem key of an ESDV has failed OR damaged in open position……. What can happen …? It will not close when there is a close command and this may lead to disastrous situation - from Piping Engineering.

 

Valve Actuator Closed Loop Breathing

Closed Loop Breathing - This is a technique to ensure that corrosive or saline air cannot enter the internals of the valve on the breathing side of the valve. It is very popular in the Offshore Oil and Gas Industry and on Coastal Refineries etc - thanks to Rotork for this excellent schematic.

 

Shutdown and Blowdown Valve Applications

Avoiding Pressure Surge Damage in Pipeline Systems - Pressure surges occur in all fluid pipeline systems. There arise two types of damage from the surge phenomenon, fatigue and catastrophic failure. This paper addresses this phenomenon from the viewpoint of the available solutions rather than the mathematics and modelling involved in determining the quantum of the surge pressure. it has some useful information pertaining to SDV/BDV valves - from Piping Design.

Redesign Blowdown Systems and Alter ESD Practices - When compressor stations are taken offline for maintenance or the system shuts down, the gas within the compressors and associated piping is either manually or automatically vented to the atmosphere (i.e., blowdown). Emergency shutdown (ESD) systems are designed to automatically evacuate hazardous vapours from sensitive areas during plant emergencies and shutdowns. Some ESD systems route these vapours to a flare stack where they are combusted, while other systems simply vent the evacuated vapours to the atmosphere via a vent stack. Partners report a number of opportunities to reduce emissions from blowdown systems and ESD practices, including (a) Redesigning blowdown systems altering ESD practices (b) Installing YALE^® Closures (c) Designing isolation valves to minimize gas blowdown volumes (d) Moving fire gates valves in to minimize blowdown volumes. Department of Transportation (DOT) regulations require that emergency shutdown (ESD) systems at gas compressor stations be fully tested on an annual basis. One common practice is to activate the entire system, which discharges very large volumes of gas to the atmosphere. A DOT acceptable alternative is to test each individual dump valve with the discharge stack blind flanged. This greatly reduces gas emissions, but has higher labor costs associated with installing and removing a blind flange on each ESD valve - from the EPA.

The Following are from Metso Automation;

• Need a Cryogenic Valve Testing Facility? - The cryogenic valve test centre at Metso Helsinki factory is one of the largest and most advanced dedicated valve test facilities in Europe. It offers customer inspectors the possibility of witnessing potentially hazardous testing operations through shockproof windows in the comfort of a protected, air controlled control room built to the latest safety standards, using a fully computer controlled and logged testing system.
• Gas to Flare System ESV & ESD Valves - Both ESD and ESV valves are commonly located in or near the process plant. The flows from different proc­esses are further lead to a flare header which is sized for the certain worst-case volume condition, assuming that relief devices discharge at the same time and other process vents may also be flowing.
• Atmospheric Distillation ESD Valves - Atmospheric distillation is the first major process in a refinery. All crude oil entering the refinery, after desalting, passes through the atmospheric distillation column on it’s way to further processing in down stream process units. If there is a shut down of the atmospheric distillation column it means that the entire rerfinery is essentially shut down. The ESD valves are located at the bottom of the atmospheric distillation column and are typically arranged as two valves in parallel piping. The fluid passing through the valves is refered to as heavy bottoms. This fluid is the heaviest cut of a hydrocarbon attainable by atmospheric distillation. The heavy bottoms pass through the ESD valves on their way to the vacuum distillation column for further processing. The ESD valves are used in the normally open condition and are expected to function reliably throughout long process runs, typically four (4) to five (5) years between shut downs.
• Oil Refinery and Other Units Processing Hydrocarbons - ESD valves with High Integrity Level - There are fire and explosion risks in the units processing flammable hydrocarbons in case the fluid comes in contact with the atmosphere. If there are high- and low-pressure sections in the plants like e.g. in refinery HDS (hydro desulphurisation) units, the low-pressure side has to be protected against high pressure in case of control failure. Traditionally the number of emergency shut-off valves (ESD) in the process lines in a refinery is not very high. With Neles ValvGuard’s partial stroke testing functionality the ESD valves are automatically diagnosed for their operability while the plant is in operation. With this technology general plant safety can be improved in a cost effective way.
• Reliable ESD Valves in Tower Bottom Lines in Heavy Oil Units - Besides fired heaters, the distillation tower bottom areas are the most fire-risky places in a refinery. When the question is of residual oils, high oil temperature, coke formation, sulphur corrosion and possible particles in the oil make the conditions even more severe. Neles metal-seated ball valve with its constructional features and the Neles ValvGuard, partial stroke testing system, used to keep the valves under continuous watch are helping to minimize the fire risks in these areas.
• High-End Intelligent Emergency Valve Applications - Jari Kirmanen - Process facilities today are facing growing challenges to meet requirements with respect to the environment, health and safety of the plant personnel while maximizing product output and quality. With increasing energy prices, process plants must further develop their processes and maximize the yield of valuable products in an energy-efficient way. Plant run-time targets are increasing, which also set more challenges on equipment reliability and safety. De-pressurizing or pressure protection, as well as burner emergency shut-off being part of the safety integrity system, is a part of the process industry’s backbone defence against a threat to personnel and equipment. Intelligent partial-stroke devices capable of diagnosing emergency valve condition are more commonly utilized in the hydrocarbon industry. General requirements and challenges together with the benefits of using emergency valves equipped with intelligent partial-stroke devices were considered in the Hydrocarbon engineer magazine article in November 2009 [1]. This article demonstrates more closely how intelligence solutions can be utilized and what kind of added value they bring by introducing three examples of high-end emergency valve applications.
• Intelligence for LNG Ball Valves - Intelligent valve technology can help to reach the most demanding targets in anti-surge control applications, where fast and accurate operation is needed at extreme service conditions with high pressure differentials and tight shutoff.

 

Shutdown and Blowdown Valve Maintenance

Onshore Condition Monitoring of Offshore Valve Assemblies - Niklas Lindfors and Jarkko Räty - Especially in the offshore sector, there is strong emphasis on minimizing the number of staff working in hazardous offshore environments, without impacting on reliability. At the same time, it is expected that the availability of production and the life cycle costs of process equipment should be optimised. These requirements create the need to improve the capability to analyse control-valve data from offshore applications - to focus and plan service actions well in advance. In other words, to enhance the utilization of existing technologies and increase the use of specialist know-how in order to enable offshore personnel to carry out the required tasks effectively, safely and with minimal labour and disturbance to the process itself. (Go to page 4 to access this information).

Increased Reliability and Safety at Czech Refinery through Partnership in Valve Maintenance - Karel Dvorak and Niko Aunio- In the past, Ceská Rafinérská’s strategy has been to carry out turnarounds every four years. This was the first time that the interval was extended to 5 years. After 9 years of operation, some problems were expected, however, on this occasion Ceská Rafinérská’s approach was different from that adopted for the previous turnaround. The control valve scope was reduced and the on/off valve scope increased to include overhaul testing based on the SIL classifications. The Metso field survey and Neles ND9000 diagnostics formed the basis for the valve turnaround planning.

 

Partial Closing and Stroke Testing

Partial Stroking on Fast Acting Applications - Willem-Jan Nuis, Rens Wolters - Partial stroking: This is a widely used method to avoid sticking of a ball valve when it is not operated for some time. It is also used to reduce the actuator size and thus the total cost of the valve + actuator - from Mokveld.

The Following are from Metso Automation;

• Partial Closing with Neles Valveguard - Safety engineers throughout the world are struggling with the problem of how to best comply with new and more stringent safety requirements. New IEC requirements state that manufacturers must determine and document precise levels of safety and furnish quantifiable proof of compliance. In light of these requirements, BP feels it is necessary to reassess its traditional safety loop testing procedures. In particular, BP feels it is important to improve its safety valve testing procedures in order to drive costs down and improve plant safety.
• Neles ValvGuard "exercises" to Keep Fit - Mark Williamson - An ESD valve, whose mechanism is not often moved, is susceptible to jamming - There is a need to test valves frequently but (with older technology) this is only possible when the process is stopped for major turnarounds, or process shutdowns. Today, the periods between shutdowns is becoming longer and longer. To ensure compliance with safety standards, maintenance engineers therefore face a dilemma. They need more valve testing but they have fewer opportunities to do it when the process is down. Also, frequent manual testing carries a high labour cost. This can be overcomes by automatically “exercising” the valve through a partial stroke at pre-programmed intervals.
• What You Need To Know About Safety Instrumented Systems (SIS) and Partial-Stroke Testing of ESD Valves - A useful document providing an overview of SIS and Partial stroke testing.
• Onshore Condition Monitoring of Offshore Valve Assemblies - Niklas Lindfors and Jarkko Räty - Especially in the offshore sector, there is strong emphasis on minimizing the number of staff working in hazardous offshore environments, without impacting on reliability. At the same time, it is expected that the availability of production and the life cycle costs of process equipment should be optimised. These requirements create the need to improve the capability to analyse control-valve data from offshore applications - to focus and plan service actions well in advance. In other words, to enhance the utilization of existing technologies and increase the use of specialist know-how in order to enable offshore personnel to carry out the required tasks effectively, safely and with minimal labour and disturbance to the process itself. (Go to page 4 to access this information).
• Depressurizing Systems used to Reduce the Failure Potential for Scenarios Involving Overheating - Sari Aronen - When metal temperature is increased due to fire, exothermic or runaway process reactions, the metal temperature can reach a level where stress rupture can occur. Depressurizing reduces the internal stress, extending the life of the vessel at a given temperature. A relief valve cannot provide adequate risk reduction or safety to depressurize a vessel: it can only limit the pressure from exceeding the process upset point. Therefore, depressurizing valves are used to reduce the risk of losing equipment integrity.

Partial Stroke Testing - Simple or Not - Vendors Promise Increase in MTBF to 13,000 Years - Is this Realistic? - Bill Mostia Jnr - This Technical Article gives an excellent overview of Partial Stroke Testing and the use of Valve Signature data - from Emerson Process Management.

Automatic Partial Stroke Testing Prevents Disasters - Janne Laaksonen - Safety engineers throughout the world are struggling with the problem of how to best comply with new and more stringent safety requirements - IEC requirements state that manufacturers must determine and document precise levels of safety and furnish quantifiable proof of compliance. In light of these requirements, manufacturing companies feel it is necessary to reassess their traditional safety loop testing procedures. In particular, they feel it is important to improve their safety valve testing procedures in order to drive costs down and improve plant safety - from SA Instrumentation and Control.

The Striking Role of Partial Valve Stroke Testing to meet Safety Integrity Levels - Bert Knegtering - Partial Valve Stroke Testing or PVST, is a concept to automatically increase the performance of Safety Instrumented Systems. PVST is a concept where safety-related valves like ESD valves and shut-off valves are automatically tested concerning failure modes that are related to valve sticking and slowing down operation. Current trends in the industry show an upcoming number of dedicated technical PVST solutions by various automation and instrumentation vendors. The added value of PVST within the process industries is a significant reduction of the frequency of required manual periodic valve proof tests, its related manual test cost and reduced spurious trips due to manual errors. Partial testing is performed by additional automated test instrumentation, which can easily be initiated and controlled by the safety-instrumented systems’ logic solver such as the safety-related PLC. This paper discusses practical examples of Partial Valve Stroke Testing in which it appears that SIL 1 rated valves can be upgraded to SIL 2, and off-line proof test intervals which can be extended from 2 to 5 years. Thanks to Honeywell.

Ensuring that your ESD Valves Work when needed - Emergency Shut-Down valves (ESD) are critical in protection of plant and personnel. These must operate in the event of plant malfunction or fire. The most important requirement for an ESD valve is it’s reliability of operation (open or close) in an emergency. By it’s very nature, it is difficult to test that an ESD valve is "available" without causing a plant upset. The plant is at risk however unless it can be shown that the valve is functioning properly. How can this be done?

 

Riser Emergency Shutdown Valves (RESDV)

Pipeline Riser Emergency Shut Down Valves - Inspection Issues and Recommendations - Regulation 19 and schedule 3 of the Pipelines Safety Regulations 1996 (PSR) require RESDVs to be capable of adequately blocking the flow and this must be achieved with a valve that is suitable and is maintained in an efficient state, in efficient working order and in good repair. The Piper Alpha disaster highlighted the critical nature and functions of riser emergency shut down valves - from HSE (UK).

Investigations into the Immediate and Underlying Causes of Failures of Offshore Riser Emergency Shutdown Valves - Riser emergency shutdown valves (RESDVs) are an essential risk reduction measure for offshore installations and are a legal requirement under the Pipelines Safety Regulations 1996. RESDV failures, whether arising from a test or a real demand, are reportable to HSE under RIDDOR and a preliminary survey found approximately 180 cases of failure. Given the criticality of RESDVs to offshore safety, it was determined that the reasons for these occurrences should be investigated with a view to focussing inspection topics and identifying areas for future improvement across the industry. Two themes have emerged from the causal analysis of RESDV failures: the age of the valves that failed, and the failure to learn and implement lessons from previous incidents. The three most common immediate causes were stated by dutyholders to be corrosion, the age of the RESDV and seizure/sticking. Nearly half of failed RESDVs have had a previous failure, and over a quarter of failed RESDVs were brought back into service after cycling and/or lubricating the valves. The root cause of the failure needs to be determined and acted upon so that it does not recur, rather than just bringing the RESDV back into service. This report and the work it describes were funded by the Health and Safety Executive (HSE).

 

Fire Safe Actuators and ESD Valve Fire Shelter

Firesafe Actuators - An essential part of equipment safety is to be able to maintain the fail-safe position when a fire breaks out. In case of pneumatic linear actuators, the fail-safe position must be assumed and maintained when air supply fails or the diaphragm ruptures. Usually, springs are used to perform this task. They force the valve to move to the fail-safe position when dangerous situations emerge or damages occur. On failure of air supply, the Actuator springs act against the pressure of the process medium on the plug to move the valve to the fail-safe position and keep it there - From Samson Controls.

Innovative Passive Fire Protection Cabinets Extend Margin of Safety for Critical Plant Shutdown Equipment - A novel new range of cabinets to protect critical process equipment in hazardous areas against very high temperature fires has been launched by the field equipment protection specialist Intertec. The cabinets ensure that equipment such as emergency shutdown valves remain operational by keeping them below 60 degrees Centigrade for periods of up to 90 minutes in the event of a hydrocarbon-based fire, to allow time for controlled shutdown. The new 90-minute protection capability - which Intertec believes to be a first in this sector of the industry - has been tested against the ANSI/UL 1709 standard by the test body MPA Dresden.

Innovative Passive Fire Protection Cabinets Extend Margin of Safety for Critical Plant Shutdown Equipment - The cabinets ensure that equipment such as emergency shutdown valves remain operational by keeping them below 60 degrees Centigrade for periods of up to 64 minutes in the event of a hydrocarbon-based fire, to allow time for controlled shutdown - from Intertek,

 

HIPPS Systems

Pressure Relief Valves and HIPPS systems - From ICEweb - These systems have been utilised in Germany for over 20 years and are proven to be extremely reliable in very rapid isolation of pipelines. However the technology is still developing to a point where the required reliability meets all users needs. They are so reliable that the need for other safety related devices such as Safety Relief Valves can be minimised. They have the following advantages.

• Negating the need for flare systems to be sized for the case of a well failing to close.
• Production piping downrating, giving potential cost benefits of more than 25%.
• Fast inventory isolation within two seconds.
• Huge capital cost savings.

Looking for Safety Instrumented Systems Technical Information? See ICEweb's SIS page.

Severe Service Valves

Go to Specific Subject : Severe Service Valve Description and Applications | Severe Service Control Valve Design for Abrasive Conditions | Severe Service Control Valve Design for Corrosive Conditions | Severe Service Control Valves on Cavitation Services | Severe Service Valves for Liquid Application | Severe Service Valves for Gas Application | Severe Service Valve Technical Papers and Articles | Severe Service Control Valves on Flashing / Outgassing Services | 

 

Severe Service Valve Description and Applications

Severe Service Valves are required where the process can cause damage to conventional valves through erosion, high noise, cavitation, high vibration, possible mechanical damage to the valve trim, other components and the process equipment around the valve. These valves are generally specialist designs that overcome these issues by "smart" design. They are generally used for such applications as;

• Wellhead Choke
• Anti-surge Compressor Recycle
• Pipeline Surge Relief control
• Separator level control - surface choke valves
• Service Water Flow Control
• Fire Water Overboard Dump Valves on Offshore Facilities
• Fire Water Deluge System
• Fire Water Pump Discharge
• Aerodynamic Noise Control
• Cavitation/ Flashing Control
• Centrifugal Pump Minimum Flow Recirculation
• Steam Conditioning
• Turbine Bypass Valves
• Gas/Oil Separator Valves
• Gas to Flare
• Emergency Blowdown Valves Import and Export valves

 

Design of Severe Service Control Valves

Coping with cavitation, abrasion, flashing, high pressure drop or noise caused by these applications require valves with specific design features which take these factors into account. The design of a Severe Service Valve uses the following methods to provide valves capable of handling the severe service process conditions.

 

Severe Service Control Valve Design for Abrasive Condition

When a fluid contains abrasive particles such as sand etc., the selected valve should have a flowpath design  which minimises turbulence and impingement.

The valve should be designed so that any of the parts subject to the process medium high velocity jet downstream of the valve orifice are specifically selected to cope with the process steam. High pressures and temperatures require specially selected valve bodies and trim.

Material selection of the valve and trim depends on the hardness of the particles, corrosion potential, angle of impingement, velocity and temperature. A typical resistant material used is Tungsten Carbide.

 

Severe Service Control Valve Design for Corrosive Conditions

Designing a Severe Service Valve to resist corrosion requires the following specification considerations;

• Select a valve and trim material that can withstand the corrosive fluid/material.
• It is good practice to select a valve design that is readily available in these materials, that is not a special which results in higher costs.
• Consider lined and diaphragm type valves, depending on the application plug or ball valves. Other than composite materials valves may be lined with tantalum or other metals, however plating is thin and subject to abrasion.
• Sometimes cheap quarter turn valves are used in the mining industry, however they require changing often and impose a high cost of ownership in maintenance and safety risk so the use of these valves these is not recommended.

 

Severe Service Control Valves on Cavitation Services

Cavitation may cause erosion, excessive noise and  vibration. Any of these may cause catastrophic failure of the control valve.  Hence severe service control valves are utilised.  As no material can withstand the effects of  imploding cavities, the severe service valve is engineered to avoid the formation of vapour cavities or prevent their implosion. The design of the valve trim thus sometimes includes;

• Streamlined flow path through the full-port expanded body avoiding turbulence and preventing erosion and vibration.
• Small flow channels and tortuous passages.

 

Severe Service Valves for Liquid Application

In liquid applications severe service valves are used where high pressure drops can cause cavitation which can quickly cause catastrophic damage to the valve trim and body. In addition erosive applications can also cause similar damage. High noise also occurs. This has severe safety ramifications if a standard control valve is utilised. 

Typical Liquid process conditions for a severe service valve on liquid application are;

• Pressure drop of more than 5 Megapascals (Mpa) - 725 Pounds per square inch (psi)
• Flashing conditions Pv - P2 more than 3 Megapascals - 435 Pounds per square inch (psi)
• Multiphase conditions P1 - P2 more than 3 Megapascals - 435 Pounds per square inch (psi)
• Abrasive or Corrosive product

 

Severe Service Valves for Gas Application

In gas applications severe service valves are used where high pressure drops can cause cavitation which can quickly cause catastrophic damage to the valve trim and body. In addition erosive applications can also cause similar damage. High noise also occurs. This has severe safety ramifications if a standard control valve is utilised.

 

Severe Service Valve Papers and Applications

The following technical papers, articles and application examples are from Mokveld.

Axial Control Valve at Compressor Station in Morocco - 12" ASME 600 Valve

Axial Surge Control Valves in Russia - Anti surge control at -60°C (-76°F)

Axial Surge Relief Valve - The high-capacity proportional pilot design allows fast response and will eliminate the dangers of a pressure surge. All components operate solely on fluid static pressure to provide ultimate protection. Owing to stable opening behaviour, pilot design and consequently high effective capacity, the valve can fully protect the piping systems against dangerous and costly surge pressure damage.

Axial Excellence in China's Gas Transmission Network - By nature of design the axial control valve has unique benefits that make the valve specifically suitable for the more special and severe service control applications. In this article, Mokveld presents some benefits of the use of axial control valves and provides some specific project application examples.

Mokveld Subsea Control Valves Service Norwegian Oil Field - One of the technology gaps to be addressed was the development of large fast-acting subsea control valves. Several operators recognised the unique advantages of Mokveld's axial flow design in topside severe service control applications and approached Mokveld to investigate the axial flow concept as the basis for a subsea control valve.  

Subsea Gas Compression with Mokveld Subsea Control Valves - Subsea gas compression is a technology approach that can boost recovery rates and lifetimes of offshore gas fields. Aker Solutions - at the forefront of subsea gas compression - was awarded the contract by operator Statoil to supply a complete subsea compression system for Norway’s Åsgard field. The project represents a quantum leap in subsea technology, and an important step in realising Statoil’s vision of a complete underwater plant.

 

Other Useful Links to Severe Service Valve Technical Papers and Articles

Control Valves for Critical Applications - Dr J Kisbauer, Samson A.G.- Know the causes of cavitation and how to prevent them. 

Large Size Quarter Turn Control Valves can Improve Safety in Pipelines - Carlos Lorusso - Most control valve applications in pipelines are related to system start-up and shut down, emergency operations, delivery control, fluid speed control for pipeline internal examination. Selection of the right control valve is a key factor for long term successful performance for large applications where the safety and security of supply are important considerations. This document presents considerations for control valve selection to improve the safety and operation of oil and gas pipelines. Axial control valves are used when high pressure drop, high flow coefficients, low noise levels and bubble tight shut-off are required. Common applications include compressor start-up, shut-down and High Integrity Pressure Protection Systems (HIPPS). Triple offset valves (TOV) are used for large volume flow control, bubble tight shutoff, pressure drops of less than 30%.Typical applications include delivery point and controlled blow down. Ball valves are used for speed control for intelligent pig travel during pipeline examination and cleaning operations - from Tyco and pipeline conference.

Avoidin Pressure Surge Damage in Pipeline Systems? - Pressure surges occur in all fluid pipeline systems. There arise two types of damage from the surge phenomenon, fatigue and catastrophic failure. This paper addresses this phenomenon from the viewpoint of the available solutions rather than the mathematics and modelling involved in determining the quantum of the surge pressure.

Are You at Risk from Not Considering the Potential for Surges in a Piping System? - Geoffrey D Stone - This article raises a number of issues in respect of the risks you may be exposed to from the requirements to consider the pressure transients in a piping system design. The risks not only relate to physical damage but also the consequential risks that arise from such damage whether it is contractual, branding or loss of use. Piping systems are designed in Australia and overseas to a number of National Codes and Standards. In addition to this there are industry bodies that publish design guides and codes that are referred to in contract documents. These require that design for surge are taken into account to determine the loads and stresses in a piping system. This paper only addresses surge events from a liquid pressure transient. Events arising from condensate in steam or gas lines are not covered here. These events may be even more catastrophic as the velocities of the liquid column are much higher than in a liquid system. If nothing, read the section on Contract Requirements and consider the risks you run by being ignorant of this engineering topic - from Ventomat Australia Pty Ltd.

Diffusing Bubble Bombs - Proper Valve Sizing for Severe Service Can Help Lessen Wear and Damage from Cavitation - Gerald Liu, PE - Instrument technicians are often called by their instrument engineers to look at repeated control valve failure problems during plant shutdowns. From a maintenance point of view, the definition of "severe service" in control valves can be based on how long the valves last - From the excellent www.controlglobal.com. 

 

Severe Service Control Valves on Flashing / Outgassing Services

Flashing occurs when the pressure drop across the valve causes a portion of the process stream to flash to a vapour. Outgassing is more complex, The paper Outgassing Versus Flashing - What are the Differences? from Emerson Process Management gives a A really good description.

Coming Soon! Professional Certificate of Competency in the Selection, Commissioning and Maintenance of Shutdown, Blowdown, Severe Service and Choke Valves Emergency Shutdown Systems (ESD) are a fundamental part of the safety systems associated with oil and gas, utility and other hazardous processes. Associated with these systems are specific valves which are used to isolate and blowdown the processes. These are referred to as Shutdown (SDV) and Blowdown (BDV) Valves respectively. Under emergency situations it is critical that these valves operate correctly. Thus the engineering of the valves and their associated actuators is paramount in ensuring plant safety. They must meet the Fire Safe and Reliability criteria determined by IEC16508 and IEC16511. This Professional Certificate of Competency (PCC) covers the requirements in detail. In addition, the course addresses Severe Service Valves and Wellhead Choke Valves. Severe Service Valves are required where the process can cause damage to conventional valves through erosion, high noise, cavitation, high vibration, possible mechanical damage to the valve trim, other components and the process equipment around the valve. These valves are generally specialist designs that overcome these issues by "smart" design. Get Further Information.

Defining Severe Service Valves - No clear or universal industry definition or mechanism exists to describe and accurately define severe service valves (SSVs) from general purpose valves, yet such a definition would allow clients to benefit from improved process performance, increased profitability, safety and environmental protection. This high level paper looks to offer an objective definition - from CGIS.

The Following links are from CCI Valves.

Fluid Kinetic Energy as a Selection Criteria For Control Valves - Herbert L. Miller /Laurence R. Stratton - A selection criteria is provided that assures a control valve will perform its control function without the attendant problems of erosion, vibration, noise and short life. The criteria involves limits on the fluid kinetic energy exiting through the valve throttling area. Use of this criteria has resolved existing valve problems as demonstrated by retrofitting of the internals of many valves and vibration measurements before and after the retrofit. The selection criteria is to limit the valve throttling exit fluid kinetic energy to 70 psi (480 KPa) or less - from CCI Valves.

Getting Optimum Performance through Feedwater Control Valve Modifications - Brian Leimkuehler, P.E./ Sanjay V. Sherikar, P.E. - Good control of the feedwater system is very important for smooth operation at nuclear power plants. The performance of the feedwater control valves, which are the final control elements, is crucial in achieving the desired level of control in the system. Modifications were made to existing feedwater control valves at a 565 MWe BWR nuclear power plant. These modifications were part of an overall system upgrade, resulting in significantly improved controllability of the Feed Water Control system. The characteristics that are critical for best performance from the feedwater control valves are : fluid velocity control at all operating conditions, high rangeability, proper flow characterization, high actuator stiffness and good dynamic response. By analysis, and observed through experience, a properly designed and maintained pneumatic control system can provide the dynamic response and resolution necessary for feedwater control performance - from CCI Valves.

Evaluation of Control Valve Performance is Necessary in Plant Betterment Programs - Sanjay V. Sherikar, Ph.D., P.E. - Control valves affect the performance of power plant in terms of output, heat rate, reliability and availability because they are the final control elements in the operation. Therefore, critical evaluation of control valves must to be an integral part of any plant betterment program because the ultimate goal of such efforts is to improve the efficiency and reduce costs. Even control valves in the few severe service applications, which affect efficiency more than the rest of the valve population, have traditionally not been included in such efforts. Recent studies indicate that eliminating control valve problems alone can improve the heat rate of power plants in the range of 2% to 5%. The elements that are critical in realizing the potential benefits are: analyzing the whole system and quantifying the losses, identifying the root causes of the problems causing these losses and then, finally, eliminating the root causes of those problems. Methods to estimate loss due to control valve non-performance have to be judiciously applied, and sometimes developed, on a case-by-case basis, as shown by examples in this paper. The commonly observed causes of valve problems are discussed, followed by practical strategies for implementing solutions to the valve problems - from CCI Valves.

Technical Specification - Control Valve. based on “Control Valves - Practical Guides for Measurement and Control” Published by ISA - This specification prescribes the minimum mandatory requirements governing the design, sizing, and selection of control valves.

Linea Pistion Actuators - Samy, Stemler - High Reliability of actuation is of paramount importance in the nuclear power industry. Pneumatic actuators form the largest installed base with many in safety significant applications. This paper addresses the issues related to actuation, such as available Thrust, Stiffness, Sensitivity, Hysteresis, Dead band, Dynamic Stability and a sizing example. This paper also presents comparisons between various types of linear actuators and their relative advantages and disadvantages. Also presented will be evaluation techniques for troubleshooting actuator problems and improving plant performance.
Specifyin the Plant’s Control Valves - Miller - The subject of this paper is the proper specification of the control valve to avoid many of the problems noted above. To provide information so that the valves’ attributes that are important for the application are noted and that over specified needs are minimised. Over specifying needs result in compromise and trade off decisions in the design and result in higher initial costs.

Technology in Severe Service Control Valves - Sherikar - Severe service control valves are critical for safe, reliable and efficient operation of power plants. Such critical applications must be looked at differently from general service control valves because these applications have their own specific set of requirements for good long-term performance. The performance limits of control valves in such services is clearly a function of the technologies in them. Discussion on severe service valves is presented in order to aid the application of correct technology in such critical services.

Specifyin Control Valves for Severe-Service Applications -  Larry Stratton and David Minoofar - This paper discusses the stringent requirements that valves must meet to safely operate and deliver long term performance under severe service conditions.

More technical papers on valve applications from CCI Sulzer can be found here.

Solenoid Valves

Go to Specific Subject: Solenoid Valve Specification | Solenoid Valve Selection Installation, Maintenance and Troubleshooting | Low Power Solenoid Valves | Solenoid Valves in Safety Instrumented Systems | Miniature Solenoid Valves | Solenoid Valves for Offshore Applications | Solenoid Valves for Miscellaneous Applications

 

Solenoid Valve Specification

The following excellent links are from ASCO.

• Considering Valve Specification & Installation, Flow Control - Best Practices & Technology to Ensure Long-Term Performance - Matt Migliore - When specifying valves for a given application, it is important to first determine the intendedfunction. A lack of functional understanding is often where valve performance issues begin.The user, rather than fully consideringthe application in which the valve will operate finds later on that the valve isn’t all that well suited to meet the needs of the job it is being asked to do.Thus it is worthwhile answering a few simple questions when considering a valve purchase.
• Solenoid Valve Technology,Technical Characteristics Function, Terminology and Construction types - A very useful overview of solenoid operation, construction, terminology and operating parameters.
• Frequently Asked Questions about Solenoid Valves - Have a question regarding solenoid valves? This excellent resource may well have the answer.
• Optimizing Power Management in Solenoid Valves - By Stephen Glaudel Vice President, Engineering ASCO Valve, Americas - This paper covers the basic operation of solenoid valves, including useful techniques and technology for optimizing performance, power consumption, and cost of operation, in either AC or DC powered applications.
• Engineering Information - Importance of Properly Sizing Solenoid Valves - It is important to properly size a valve as there are undesirable effects in both undersizing and oversizing. This technical information sheet also includes the definition of Kv, data on Flow Data, Flow Factor, Orifice Size and sample problems. 
• Solenoid Valve Engineering Information - This excellent engineering information sheet details most of what you need to know in regards to selecting a solenoid valve.  It details maximum/minimum pressures and temperatures, viscosity, response times, valve seat tightness and degrees of protection provided by electrical enclosures (IP code).
• Solenoid and Pressure Operated Valve Technology - Function, Terminology and Construction Types.
• Proportional Solenoid Valves - Most flow control valves work on an “on/off” basis. They are either fully open or fully closed. Proportional valves, however, operate with a “proportional” action. By varying the electrical input to a proportional valve, the flow of the fl uid through the valve can be continuously and steplessly adjusted between 0 to 100% of the maximum rated flow.
• Valve Sizing Calculator from ASCO - This calculator provides options for liquid, gas and steam and also has conversion tools.
• Rubbers, Plastics and Metals used in Solenoid Valves - Technical Information Sheet.
• Chemical Resistance Guide - A useful Technical Information Sheet - ASCO valves are available to control most acids, alcohol, bases, solvents and corrosive gases and liquids. Modifi ed or special designs are sometimes required depending upon the fluid and application. Corrosion occurs either as a chemical or electro-chemical reaction. Therefore, consideration must be given to both the galvanic and electromotive force series, as well as to pressure, temperature and other factors that might be involved in the application. This guide provides information on most common corrosive and non-corrosive, unmixed gases and liquids.
• Solenoid and Pressure Operated Valve Technology - ISO 1219 Symbols - Symbols used for different combinations of Solenoid Valves. Solenoid Operators, Coils and Spare Parts Kits - Coil identification and basic design considerations.
• Solenoid Engineering Information -  Maximum/minimum pressures and temperatures viscosity, response times, valve seat tightness degrees of protection provided by electrical enclosures (IP code).
• Useful Engineering Conversion Tables for Solenoid Valves
• Understanding European versus U.S. Temperature Code Ratings for Solenoid Operated Valves - Manny Arceo - Solenoid valves are vital components of many process automation systems. Users must depend on these valves to operate flawlessly in hazardous or explosive environments; to comply with safety regulations; and to stay up and running for continuous, safe operation of the process and the plant. Understanding the differences between valves is critical in specifying and selecting the correct models. That’s a useful skill for end-user application and process engineers, as well as for design engineers employed by original equipment manufacturers (OEMs). However, such understanding can be hard to come by. Particularly difficult for many buyers to work with: differences in valves’ temperature ratings. These T-code ratings are assigned by approval agencies in the U.S., Europe, and other regions worldwide as industrial globalization increases. This paper examines and explains differences among the world’s major temperature ratings for solenoid valves. (Note that the ratings may apply to some other electrical devices as well.) It should serve as a concise guide to understanding and applying these ratings in order to correctly specify these components.
• Solenoid Pilot Valves for Valve Actuation -  Bill Reeson - This paper helps users select the correct pilot valve construction for an application - Thanks to ASCO and valve magazine.
• Understanding Applications, Uses Key to Solenoid Valve Selection, Plant Engineering - David Zolobinski, William Mudd and Gregory Byrne - This paper covers common applications and issues associated with solenoid valves. It also has a very useful trouble shooting guide plus a section on new developments - Thanks to ASCO and www.plantengineering.com .

Other Links

Need Solenoid Valve Information? - This website a comprehensive source of solenoid valve information Direct-acting, semi-direct acting, pilot-operated, pinching-type, latching-type, normally open, and normally closed valves are all different types (or sub-types) of solenoid valves. Knowing the basics about each type will help you to choose the correct one for your application - from Solenoid Valve Info.

Understanding Solenoid Valves - Solenoid valves are highly engineered products that can be used in many diverse and unique system applications. A brief overview of the components and functional varieties of solenoid valves  - from achrnews.

Technical Principals of Solenoid Valves from Omega.com

Solenoid Valve Engineering Information from Spartan Scientific

Solenoid Valve Common Symbols - From Connexion Developments Ltd

Solenoid Valve Seal Basic Guide - Selecting the correct sealing material for your solenoid valve requires an understanding of available sealing materials. Seals are usually the most limiting factor of a solenoid valve. The seal selection should take the following items into consideration;
- Chemical properties of the media
- Temperature of the media
- Pressure to be used
From solenoidvalvesuk

 

Solenoid Valve Selection Installation, Maintenance and Troubleshooting

The following excellent links are from ASCO.

• How to Install, Troubleshoot  and Maintain Solenoid Valves - Good Installation and Maintenance Tips.
• ASCO "Red Hat" Solenoid Valves - Selection, Installation. Maintenance and Troubleshooting - This document from ASCO Canada provides some useful information.
• ASCO Solenoids - General Operating / Maintenance Instructions / Troubleshooting Guide and Spare Part Kits.
• Not Your Father's Valve - "The Old Iron Workhorse Gets a Makeover" - Matt Migliore - This article highlights how microprocessors are enabling the development of smaller and faster solenoid valves. 

Other Links

To Repair or Replace? - Solenoid Valve Maintenance & Troubleshooting Strategy - Michael D’Amato - The small yet robust solenoid valve is a powerful electromechanical gatekeeper. It has the important task of controlling the flow of liquid, air, gases or particles for a larger system. Yet even the most reliable of valves can fatigue or become inoperable, thus shutting down or affecting a system’s performance. As with any mechanical apparatus, proactive maintenance of a solenoid valve can extend life and ensure consistent operation - from flowcontrolnetwork.com.

Solenoid Valves Trouble Shooting Guide & FAQ - A useful troubleshooting guide from solenoidvalvesuk.

 

Low Power Solenoid Valves

How New Low-Power Solenoid Valve Technology Changes The Game - Fabio Okada, Jack Haller, and Manny Arceo - Process plants worldwide often place considerable reliance on low-power solenoid valves. They are used as pilot valves to open and close larger ball or butterfly valves, or on control valves (installed between positioner and actuator) for fail-safe air release if there’s a loss of power. They work by pressurizing or depressurizing associated actuators. A new generation of even lower-power valves is now changing the rules of the power consumption game. These products are of interest to designers working for original equipment manufacturers (OEMs) and valve assemblers, as well as for end-user engineers anyone who specifies solenoid valves for projects in refining, upstream oil and gas, chemicals, pharmaceuticals and life sciences, food and beverage, and power. This report taps the expertise of manufacturers at the forefront of low-power solenoid valve technology. It shows how innovation is offering new possibilities - and challenges - via topics such as integrated solutions, clogging and other reliability issues, usefulness in point to point and bus networks, other cost savings, remote applications, and relevant industry standards. Finally, it suggests which characteristics buyers should seek out in selecting the newest - and most consistently dependable - low-power valve technologies - from ASCO.

Current Concerns How Some Supervisory and Leakage Currents Can Affect Today’s Low-Power Solenoid Valves - Manny Arceo and Jack Haller - As fluid automation users embrace the advantages of new devices that draw unprecedentedly low levels of power, a few users are experiencing application issues that don’t occur with older, higher-power-consumption equipment. These issues center around supervisory and leakage currents generated by input/output (I/O) control systems. Such currents can cause problems when interacting with new low-power components such as solenoid valves and sensors. This paper will review concerns that can arise when applying low-power and electronically enhanced solenoid valves within certain control systems. It will outline the limited set of cases where problems can exist, and explain how to identify such cases. Finally, it will provide tips and suggestions for possible workarounds or solutions that users might consider after consulting I/O system manufacturers or their manuals- from ASCO.

 

Solenoid Valves in Safety Instrumented Systems

The following excellent links are from ASCO.

• Safety Manual for Safety Integrated Systems - This Safety Manual provides information necessary to design, install, verify and maintain a Safety Instrumented Function (SIF) utilizing an ASCO Redundant Control System, RCS. This manual provides necessary requirements for meeting the IEC 61508 or IEC 61511 functional safety standards.
• Functional Safety Solutions for the Process Control Industry - ASCO solenoid pilot valves are an integral part of the final control element for any safety instrumented system (SIS) or critical application. ASCO offers 3 solenoid pilot valve solutions that are widely used in the process control industry; individual 3-way pilot valves, manual reset valves, and redundant pilot valve systems. Each of these solutions are proven in use as a pilot valve in critical applications and in safety instrumented systems. Certified pilot valves per IEC 61508 Parts 1 and 2 are rated SIL3 capable for domestic and international markets (ATEX). ASCO understands the need to keep your process running, but also understands that the process must shut down when commanded.
• Eight Critical Factors in Purchasing Offshore Pilot Valves - Fabio Okada and Emma Tejada - Stainless steel pilot valves play small but critical roles in the control of offshore platforms and other demanding oil and gas production operations. Acting as pilots for process and larger emergency shutdown (ESD) valves, these valves are typically installed in a platform’s pneumatic logic control panels. The valves are usually exposed to salt water and other challenging elements, so valve manufacturers all standardize on 316L stainless steel valve bodies. Panel builders, assemblers, OEMs, contractors, and end users can choose from a wide variety of models, including air-operated, manually operated, solenoid-operated, and many more. Specifiers and buyers must consider all the critical factors that bear on a given design’s reliability. The April 2010 platform loss and oil spill in the Gulf of Mexico have only sharpened the industry’s focus. In the case of pilot valves, this means that operators must have robust valves that perform efficiently each time, every time. This report considers several problems that interfere with the efficient, reliable performance of conventional pilot valves in offshore use. It also highlights design changes that have addressed these problems in newer models. Note: Onshore drillers may also specify these valves, taking advantage of their robust construction or consolidating purchasing when operating both onshore and offshore sites.
• The Insiders’ Guide to Modular Gas Valves - Gerry Longinetti and James Chiu - Fuel gas shutoff valves represent the main line of defence in combustion devices such as burners and boilers. They’re key to the safe operation of equipment for non residential comfort heating, commercial and industrial heating, and power and steam generation applications worldwide. While conventional modular gas valve designs are popular and effective, the latest generation of valves has even more dramatic improvements. Recent technological advancements in models such as new modular gas valves from ASCO offer breakthrough features and benefits. These include higher flows, more compact footprints, and greater modularity and flexibility to enable downsizing of fuel train components, as well as broader temperature ranges, higher close-off pressures, more immediate availability, and reduced costs of ownership. Tapping the expertise of valve manufacturing insiders, this report reveals how original equipment manufacturers (OEMs) and end users alike can take maximum advantage of these new factors. It’s intended to offer useful guidance in choosing the right valve for a variety of vital applications.
• Effective Compliance with IEC 61508 When Selecting Solenoid Valves for Safety Systems - David Park and George Wahlers - Certified solenoid valves properly used in Safety Instrumented Systems are important elements of any corporate risk mitigation strategy. This report addresses these issues in developing a compliant SIS using valves and Redundant Control Systems. Making the right choices in safety system planning and in valve supplier selection can affect design time, costs, and effort - as well as the safety of the plant itself.  

Other Links

How to Specify Solenoid Valves for a Particular Safety Integrity Level - S.A. Nagy - Selection must be done with care and understanding of safety and reliability standards to avoid the risks associated with an operational failure of a critical plant system - thanks to chem.info.

 

Miniature Solenoid Valves

The Insider’s Guide To Applying Miniature Solenoid Valves - Equipment designers frequently must incorporate miniature solenoid valves into their pneumatic designs. These valves are important components of medical devices and instrumentation as well as environmental, analytical, and similar product applications. However, all too often, designers find themselves frustrated. They face compromise after compromise. Pressure for increasingly miniaturized devices complicates every step of the design and valve selection process. And missteps can wreak havoc. How do designers balance the needs for reliability, extended service life, and standards compliance against often-contradictory performance requirements such as light weight, high flow, and optimum power use? This report consolidates the expert views of designers and manufacturers with wide experience applying miniature solenoid valves for myriad uses across multiple industries. It presents a true insider’s guide to which requirements are critical for common applications. It also highlights new valve technologies that may lessen or eliminate those troubling compromises - from ASCO.

 

Solenoid Valves for Offshore Applications

Stainless Steel Pilot Valves for Offshore Applications - The series’ unique design eliminates the dormancy or “sticking” problems that can occur in control valves installed in the pneumatic logic panels that control monitoring safety systems in offshore oil and gas production facilities - from ASCO.

 

Solenoid Valves for Miscellaneous Applications

The following excellent links are from ASCO.

Solenoid Valves for Low Temperature Applications

Cold Hard Facts: Five Key Criteria for Selecting Low-Temperature Valves - Bob Cadwell - This paper examines five key qualities to look for when purchasing valves, cylinders, and other fluid automation devices for application in low ambient temperatures.

Solenoid Valves for Oil and Gas Heating Equipment

Breakthrough Solenoid Valve Technology for Upstream Oil and Gas Heating Equipment - Bob Cadwell, Gerry Longinetti, and James Chiu - Low-temperature stainless steel fuel shutoff valves are usually utilized for on/off control of fuel gas within gas fuel trains in process heating system burners. These systems are widely used by oil and gas firms as well by as original equipment manufacturers (OEMs) that produce gas heating equipment or burner management systems (BMSs) and controls in upstream oil and gas pipelines and tanks. For valve manufacturers, these uses present a relatively specialized, rather challenging application. Environmental conditions at the point of use are often difficult. Ideally, valves should deliver reliable operation despite constraints on factors ranging from power consumption to service availability. Conversely, outdated controls can pose problems -  including poor performance, noncompliance with current regulations, and triggering of environmental concerns. In recent years, a new generation of solenoid valve technology has been changing the shutoff valve game. Their modern designs provide pipeline and tank heating systems with robust, durable performance; safety; and regulatory compliance - all while increasing efficiency and productivity.

Potable Water

How New Lead-Free Regulations Will Impact Your Selection Of Potable Water Valves - Paola Gutierrez - Recent legislation in several states has tightened regulation of lead content in the components of potable (drinkable) water treatment systems. Other states may well be considering similar moves. This pace of regulation seems unlikely to slacken. The message from regulators is clear: Get the lead out. However, what options are open to construction end users and original equipment manufacturers (OEMs) of these systems? Construction managers don’t make the equipment they install. And OEMs often assemble most of their systems from already manufactured components. Of compliant components they can specify, which currently meet their requirements for price, reliability, and performance? This report examines the choices facing specifiers and purchasers of small solenoid valves for potable water systems. It weighs the advantage and disadvantages of brass, plastic, and stainless steel designs. Finally, it suggests the solutions that smart planners should consider for current and future use.

Understanding the New United States Lead-Free Water System Regulations and Choosing Valves to Comply - Anne-Sophie Kedad-Chambareau - In the U.S., regulations governing lead content of the components of potable water systems have seen considerable changes as safety restrictions tighten. The federal law in effect since January 2014 dictates much lower lead content for certain systems and components than in the past. Manufacturers of potable water equipment and systems - including drinking water fountains, R/O (reverse osmosis) systems, coffee machines, and commercial kitchen equipment - as well as equipment maintenance contractors are affected. Many remain uncertain how the new regulations will impact their manufacturing and purchasing. This report outlines relevant sections of the law. It then focuses on the choices facing specifiers and purchasers who need to select important components of these systems - two-way solenoid valves - to comply. It considers the calculations that must be made to determine average lead content. Finally, it discusses the pros and cons of common valve materials (brass, composite/plastic, stainless steel, and lead-free brass), as well as other selection advantages. Original equipment manufacturers (OEMs) and contractors will get useful information to ensure their equipment remains efficient, safe, and compliant.

Reverse Osmosis Systems

Seven Things You Must Know Before Selecting Solenoid Valves For Your Reverse Osmosis System - Anne-Sophie Kedad-Chambareau , Roy Bogert and David Park - Membrane-based reverse osmosis (RO) filtration systems offer valuable service in a wide variety of industrial and commercial settings. They purify water, improve taste, and provide savings in food and beverage processing; increase energy efficiency in boilers; and supply a range of other benefits in applications from water jet cutting, vehicle washing, and humidification to restaurant and grocery use. One important component of these systems, typically used at several critical points, is the solenoid valve. Design engineers working for original equipment manufacturers (OEMs) face multiple options-and issues-when selecting these complex, highly engineered devices for their systems. Beyond the usual considerations of correct sizing and wattage, experienced designers are aware that many current models may exhibit worrisome performance problems, as well as difficulties relating to certifications, availability, ease of assembly, and support, among others. Fortunately, valve technologies are now available that avoid many or all of these problems, while providing significant benefits for OEM and end user alike. This report guides designers and specifiers in choosing the right valve to make a major positive impact on budgets, equipment life, and time to market.

Steam Valves

Seven Breakthrough Advantages of New Steam Valve Technology - Anne-Sophie Kedad-Chambareau and Gerry Longinetti - Solenoid based valves that control the flow of steam and hot water are critical components for original equipment manufacturers (OEMs) and end users of commercial and industrial laundry, sterilizer, boiler, dishwasher, and food preparation equipment. Until recently, specifiers and users of even the best traditional valve technology had to accept certain limitations. For instance, flow rates were relatively constrained, so throughput was restricted. Valve life was also comparatively short, and maintenance or replacement somewhat time-consuming. Recently, these barriers have been breached. New approaches and technologies, incorporated into a new generation of products, are changing what buyers can expect. Even differences in basic specifications can be considerable. In recent head-to-head testing of a popular traditional valve versus a new model, the new valve’s ambient temperature range was wider. Compared to some older designs, maximum temperature can be improved by 60° F and pressure can be more than doubled. The newest designs combine several features proven to offer significant benefits in traditional valves, such as threaded bonnets, a floating PTFE diaphragm, and a zero minimum operating differential design. They also add innovative new approaches such as optimized geometry, DC construction, and a lower power coil. For major performance factors, the improvements may be dramatic. This report demonstrates how choosing the right next-generation steam valve can deliver benefits such as 60% higher flow rates, four times longer life, and more.

Hot Water and Steam Service - An absolute "mine" of information about all things associated with steam.

Understanding IEC Aerodynamic Noise Prediction for Control Valves

Floyd D. Jury
Technical Consultant, Fisher Controls International, Inc.

ICEWeb thanks Fisher Controls for permission to include this article

In 1995, the International Electrotechnical Commission (IEC) released International Standard IEC 534-8-3 which is designed to calculate a sound pressure level for aerodynamic noise pro-duced by a control valve. This internationally approved and accepted standard is important because it provides a method for comparing one control valve to another on a common basis. This frees the end user from the burden of deciding which control valve vendor has the best proprietary noise prediction method. An additional advantage of the standard is that all government regulatory bodies will accept the resulting noise calculations.

Although the standard is an easy-to-use document for making aerodynamic noise calculations, it is not a good learning tool. It has little explanation and many equations with little apparent continuity. This Technical Monograph (TM) is designed to provide the user of the IEC standard with a fundamental understanding of the theory behind the standard.

At first glance, IEC 534-8-3 (hereafter referred to as "the standard") would probably lead one to believe that it is just a jumbled mass of empirical equations. Actually, the standard is based on a combination of fundamental theory from the academic fields of thermodynamics and acoustics. The basic equations which are developed from this theory are then modified by experimental results.

The IEC standard basically outlines a five step procedure for calculating noise. While the details and equations of each step often change with the flow regime involved, the general principle does not. The five steps are as follows:

Step 1

It’s the mechanical power resident in the fluid at the vena contracta of the valve which gets converted to noise. So, the first step is to determine how much mechanical power is resident in the flow stream at the vena contracta.

Step 2

Most of the mechanical power at the vena contracta is converted to heat, but some of it is converted to noise. Empirically derived acoustic efficiency factors are used to determine how much noise power is generated downstream of the valve.

Step 3

Once we know what the sound power is in the flowing medium we can use conventional theory to convert this sound power to sound pressure level in the fluid downstream of the valve.

Step 4

In order to determine how much of the sound pressure level gets transmitted through the pipe wall to the outside air, we must deal with the transmission losses involved in the passage of the sound through the pipe wall. As we shall see, these transmission losses depend upon many different properties of both the fluid and the pipe. The sound pressure level immediately outside the pipe wall is then converted to an A-weighted sound pressure level.

Step 5

Finally, standard acoustic theory is used to deter-mine how much of this sound pressure level gets transmitted to a hypothetical observer located at the standard location, which is one meter downstream from the valve and one meter away from the outer surface of the pipe.

Understanding these five steps, which are always the same for every application, provides the continuity needed to success-fully work through the standard for any given valve noise application. Let’s turn now to developing a clearer under-standing of what exactly is involved in each of these steps.

Step 1 - Determine the stream power at the vena contracta.

The noise generated downstream of the valve comes from the dissipation of mechanical energy in the fluid stream at the vena contracta of the valve. We can determine this mechanical energy by using the common equation for calculating kinetic energy of any moving mass. This equation from basic physics is simply one-half the mass times the square of the velocity of the mass.

Since we are interested more in power than we are in energy, we need only recall that power is the time rate of energy. Thus, if we use the mass flow rate in this equation instead of the mass, we will be able to calculate the mechanical power of the fluid stream at the vena contracta, just before any dissipation to noise occurs; i.e.,

Stream power of the mass flow, Watts

The energy equation from the First Law of Thermodynamics provides a convenient way to calculate the velocity of the fluid stream at the vena contracta. Several assumptions are made to further the calculation. For example, it is assumed that there is no elevation change between the vena contracta and the valve outlet (or if there is, it is negligible).

Because the change from the inlet conditions to the vena contracta takes place too rapidly for any significant heat trans-fer, we can safely assume this to be an adiabatic process. There is no work done by the fluid on anything outside the system, and finally, to simplify the calculation, we can assume the fluid velocity at the inlet to the valve is negligible compared to the velocity at the vena contracta. This is a standard assumption in many thermodynamic problems.

It is normally a lot easier to deal with pressures and specific heats, etc. than to deal with enthalpy. This transition can be accomplished if we make some additional assumptions. It is common in many thermodynamic problems to assume that real gases can be represented by the ideal or perfect gas law. This assumption is well within the normal engineering accuracy domain. In addition, it is common to assume that the specific heats are constant over the process. Finally, it is assumed that the process from the valve inlet to the vena contracta is a reversible process which we have already assumed to be adiabatic. Isentropic is a name given to reversible adiabatic pro-cesses.

Step 2: Convert to noise power at the valve outlet.

As the fluid expands from the vena contracta into the down-stream piping, some of the mechanical power at the vena contracta is converted into turbulent noise. This conversion to noise is an extremely complex process which is very difficult to accurately determine in an analytical manner. For this reason, experimentally determined acoustic efficiency factors are used.

In general, the acoustic power developed downstream of the vena contracta is determined by multiplying the vena contracta stream power by an experimentally determined efficiency factor as follows;

NOTE: Low acoustic efficiency is desirable. This means less stream power is converted to noise.

Step 3: Determine Sound Pressure Level In The Downstream Flow

The noise standard gives a definition of different flow regimes in equation form, but Figure 1 gives a better visual description of these flow regimes. Since a single acoustic efficiency factor cannot be developed that will accurately cover the entire range of possible flow conditions, a separate acoustic efficiency factor is determined for each flow regime. In general, these acoustic efficiency factors are dependent primarily upon Mach number and valve recovery characteristics.

Figure 1: Flow regimes

The actual noise production mechanisms present in a control valve are complex enough to give even the Phd’s a headache trying to think about them. No matter. It’s not really important that we understand the precise mechanisms involved as long as we can have a basic appreciation for what is happening.

There are primarily two principle noise mechanisms. In flow regimes 1-3 the primary noise mechanism is due to the turbulence downstream of the vena contracta. This is called, "Turbulent shear flow." As the flow gets more intense due to the higher pressure drop across the valve and we begin the move to higher flow regimes (3-5), the normal shock begins to move further downstream and starts to break up into several smaller shock cells. From each of these shock cells, shock waves are formed which travel downstream at some angle with the centerline. These shock waves bounce off the pipe wall and are reflected across the pipeline to reflect off the opposite wall. As these reflected waves go bouncing down the pipeline, they pass through the area of turbulence creating noise energy and imparting vibrations to the pipe wall as they go. This is called, "Shock-turbulence interaction."

In the final flow regime (V), the noise generated is no longer a function of pressure. This is called the region of constant efficiency.

It is worth noting that the majority of valve applications fall into flow regimes I or II.

Step 4: Determine the A-Weighted Sound Pressure Level Outside Pipe

Since our ultimate goal at the observer’s ear is sound pressure level rather than sound power level, we need to make the con-version from power level to pressure level for the noise in the downstream gas. First, we need to know the actual pressure disturbance (p_d) which occurs in the downstream gas as a result of the noise power we have calculated. This can be easily obtained from the basic acoustics equation relating sound power and sound pressure shown below.

Theoretically, the noise power generated in the fluid radiates outward in all directions; however, in the usual control valve, little noise travels through the wall of the valve. The noise of interest is only that which travels downstream of the valve inside the pipe, and then escapes through the wall of the pipe.

Consequently, the assumption is made that only one-fourth of the total power calculated is directed downstream and distributed over only a portion of a spherical surface which is equal to the cross sectional area of the pipe. Once we know the actual pressure disturbance (p _d) due to the

downstream noise, we can compare this to the standard Pres-sure reference for the threshold of hearing (p_o= 2 x 10_-5Pa) to determine the sound pressure level using the following relationship

So far, this has only determined the sound pressure level in the gaseous fluid inside the pipe. Noise generated inside the pipe is of little concern until it gets outside the pipe. To do this, the noise energy inside the fluid stream must cause the pipe wall to vibrate so as to disturb the surrounding air and produce sound waves that will impact on an observer.

As the pressure waves go spiralling down the pipeline and bouncing off the pipe walls, they impart some energy to the pipe wall which causes it to vibrate. As the pipe wall vibrates, it disturbs the air layer which is in contact with the outside surface of the pipe. These air pressure disturbances at the pipe wall, of course, result in a sound pressure level at this location. Not all of the sound inside of the pipe gets outside the pipe, however. Some is lost in the transmission through the pipe wall.

Figure 2: Pipe Transmission Loss Spectrum

Determining the sound transmission loss through the pipe wall is a very complicated process and only a

handful of people in the world really understand how it works. A simplistic state-met can be made that a statistical approach is used to perform an energy balance; i.e., energy in equals energy out. The devil is in the details of course, and if you wish to delve into those details you will find them documented in a paper by Dr. A.C. Fagerlund and Dr. D.C. Chou

The transmission losses through the pipe are a function of the downstream fluid properties as well as the pipe properties. As a result, the transmission loss varies with frequency of the noise as shown in Figure 2. For typical valve piping systems, the slopes of this transmission loss curve stay the same. Thus, there are only two critical parameters which completely define this transmission loss spectrum for a given situation, and they are the first-coincidence frequency (f_o) and the ring frequency (f _r). The first step then in determining the transmission loss for a specific situation is to determine these two frequencies for the given conditions. There is actually a third parameter involved in this spectrum

(i.e., the cut-off frequency f_c); however, this parameter is not invoked in the standard. It is included here only for the sake of completeness. These three frequencies always maintain the same relationship to each other as follows.

f c < f o < f r where

f c = Cutoff frequency
f o = First coincidence pipe frequency
f r = Ring frequency

Cutoff Frequency

Recall that frequency (f) is inversely proportional to wave length (l). Thus, as the frequency gets lower, the wavelength gets longer. When the wavelength is equal to (or longer than) the diameter of the pipe, the whole wave (or some portion thereof) is able to travel down the pipe as a simple plane wave. In this case there is no component of the wave which can exert any pressure fluctuation against the pipe wall and cause any vibration. Thus, for frequencies at (or below) the cut-off frequency, there is no way for the noise inside the pipe to get transmitted outside the pipe wall. In other words, the pipe transmission "loss" is infinite and we don’t need to worry about any noise at frequencies below the cut-off frequency.

First Coincidence Pipe Frequency

At frequencies above the cut-off frequency, the wavelengths are shorter than the diameter of the pipe. Consequently, the waves tend to travel down the pipeline at different angles with respect to the centerline of the pipe. This means that a particular wave will only travel so far before it bounces off the pipe wall and imparting some energy to the pipe wall in the process.

As the wave bounces off one wall, it is reflected across the diameter of the pipe to bounce off the opposite wall and so on as the wave moves down the pipeline in a spiralling fashion. As a result of the energy transmitted to the pipe by the pressure wave in the fluid, a corresponding stress wave is set up in the pipe wall. This stress wave in the pipe wall spirals down the pipeline in concert with the spiralling pressure wave in the fluid.

If a fly was sitting on the exterior surface of the pipe, it might very well be able to feel the undulations of the pipe surface as the wave goes travelling past. The frequency of these undulations, of course, would depend upon the frequency of the sound wave in the fluid which causes these pipe wall undulations. The undulations which the fly would experience are not due to bending of the whole pipe, but merely localised flexing of the pipe wall as the stress wave travels down the pipe.

Because of the material and geometric properties of the pipe, there will be some "natural" frequency of the pipe wall where the pipe will tend to go into a "resonant" mode. As a result, it takes less energy to excite the pipe at this frequency. Conversely, a given amount of exciting energy will produce a greater amount of vibration amplitude at this frequency. Of course, there are higher frequency harmonics of this frequency as well, but the majority of the energy transmission will occur at this "first" or fundamental frequency.

When the frequency of the spiralling pressure wave in the fluid (and the concurrent stress wave in the pipe) exactly "coincides" with the fundamental resonant frequency of the pipe, we will generate the greatest amplitude of pipe wall vibration from this particular stress wave. This frequency is called the "first coincidence pipe frequency."

Since the pipe wall amplitude is greater at this frequency, a greater amount of noise will be transmitted through the pipe wall at this frequency. Another way of stating this is that the transmission "loss" will be lower at this frequency.

Ring Frequency

Figure 3: Ring Section of Pipe

Imagine a "ring" section of the downstream pipe as shown in Figure 3. Image further that the applied force shown in the figure is a sinusoidal force created by the effect of the fluid sound pressure waves continuously bouncing off the wall of the pipe at some frequency determined by the frequency of the sound wave. This will cause a corresponding sinusoidal stress wave to travel around the circumference of the pipe.

As this stress wave continues to travel on around the ring back to its starting point, the stress wave arriving back at the starting point will either add to or subtract from the stresses being generated by the next wave striking the pipe wall.

When the distance between wave peaks (wavelength) is exactly equal to the circumference of the pipe, the first stress wave which arrives back at the starting point will be "in phase" with the stress wave created by the following wave. This, of course, will result in a resonant condition which greatly increases the amplitude of the pipe wall motion. The frequency where this "in-phase" reinforcement occurs is called the "ring frequency" and it will occur when the wave length of the stress wave is exactly equal to the circumference of the pipe.

Peak Frequency of the Noise

Since we have already been given the pipe transmission loss spectrum, we only need to know where the frequency of the noise falls with respect to this spectrum so we can determine how much of the generated noise will get transmitted through the pipe wall to become noise in the observer’s environment.

Aerodynamic noise generated in a control valve has been experimentally shown to produce a noise spectrum which is essentially shaped like a haystack as illustrated in Figure 4. The peak noise level of this spectrum occurs at a frequency called, logically enough, the "peak frequency (f _p)."

Figure 4: Peak Frequency

Strouhal, an early experimenter in turbulent flow, discovered that the tone frequency of turbulent noise could be given by the equation shown here.

The Strouhal experiments showed that the frequency of a single tone generated by turbulent flow is proportional to the fluid velocity and some characteristic dimension. The proportionality factor (S_T) is known as the ‘Strouhal number." Since the standard is interested in the fluid noise generated by a jet through a nozzle opening, the fluid velocity used is the velocity at the vena contracta of the jet, and the characteristic dimension, of course, is the diameter of the jet. Further experiments have shown that the peak frequency (f_p) of the "hay-stack" spectrum for control valves occurs at S_T= 0.2.

The standard assumes that the noise level at the peak frequency is the most important and essentially ignores the noise level generated at other frequencies in the haystack spectrum. This, of course, is just a first level approximation which produces acceptable results. This approach can be justified by recalling that noise levels do not directly add to each other, but combine logarithmically. Thus, the peak noise level will tend to dominate with only minor contributions from the other frequencies. A correction factor is added later in the standard procedure to account for the contribution from these other frequencies.

Calculating Transmission Loss

A direct calculation of transmission loss at any frequency is an extremely complicated affair. Dr. Fagerlund, in the work previously referenced, has developed an equation for the IEC standard which allows calculation of the transmission loss at the Ring Frequency. This calculation, used in conjunction with the transmission loss spectrum, allows one to extrapolate the Ring Frequency calculation to any other point on the curve. Since there are only three straight line regions in the transmission loss spectrum, this adjustment is a simple extrapolation using the slopes of the transmission loss spectrum and the distance along the frequency axis. Since most multi-hole noise

reduction trims accomplish much of their noise reduction by shifting the noise to a higher frequency, it is often the case that the noise peak frequency is located above the ring frequency as shown in Figure 5.

Figure 5: Transmission Loss Calculation

It is obvious that this frequency shift produces additional trans-mission loss which reduces the external noise level, but it has the added advantage of placing the peak noise frequency above the normal range of human hearing where it is less offensive.

Once the transmission loss through the pipe has been calculated, this loss can then be subtracted from the sound pressure level inside the pipe. The result is the sound pressure level in the ambient air immediately outside the pipe wall. Using standard acoustic adjustment factors, this sound pressure level can be easily changed to a A-Weighting sound pressure level.

Step 5: Translate Pressure Level toStandard Observer Location.

We can now conveniently think of the vibrating pipe wall as a new noise source. As the sound radiates outward from the pipe, which is essentially a line source, we can imagine a series of cylindrical wave front surfaces of ever increasing diameters. Figure 6 illustrates one such cylindrical wave front located at the observer’s location, one meter away from the outside of the pipe.

Figure 6: Noise at the Observer Location

Since sound power level stays constant as it flows outward, the sound power level at each wave front surface is the same as any other, however, this power gets distributed over a larger and larger surface area as we get further and further from the source. This means that the amplitude of the pressure disturbance is decreasing with distance from the source. For a given length (L) of pipe, the surface areas of the pipe and one meter imaginary cylinder are respectively

These formulas give the surface areas of the respective cylinders at the surface of the pipe (A _p and at the one meter distance (A_c).

Combining the sound pressure terms at each of these surfaces and using the sound power formula utilised previously, we can write an expression for the sound power at each of these surface areas.

Furthermore, we can logically assume that the air density (r) and the speed of sound (C ) are the same in the air at the external pipe wall and only one meter away at the observer. When these terms cancel, we see that the pressure disturbance at the observer location is simply the pressure disturbance at the pipe wall modified by the ratio of the areas involved. As a result, we can then finally calculate the Sound Pressure Level (SPL) at the observer location as a function of the known sound pressure level at the external pipe surface.

Advantages of the IEC Standard

The IEC 534 noise prediction standard provides an accurate and objective approach to calculating aerodynamic control valve noise. The IEC standard is accepted worldwide. Some international companies require its use as a condition of purchase. The standard can be used for any manufacturer’s valves. Use of the IEC standard "levels the playing field," and allows purchasers of control valves to have an objective basis to com-pare competing offers.

1 A.C. Fagerlund & D.C. Chou, "Sound Transmission Through a Cylindrical Pipe Wall," Journal of Engineering for Industry,Vol. 103,November1981,pp355-360

Definitions

A	Flow passage area, m2
Ap	Pipe surface area, m2
Ac	Wave front surface area, m2
C	Speed of sound, m/s
Cp	Speed of sound at pipe, m/s
Cc	Speed of sound at observer, m/s
Di	Internal pipe diameter, m
Dj	Vena contracta jet diameter, m
fc	Cutoff frequency, Hz
fo	First coincidence pipe frequency, Hz
fr	Ring frequency, Hz
L	Length of pipe section, m
m	Mass flow rate, kg/s
Pd	Sound pressure variation, Pa
Po	Reference sound pressure, 2x10-5Pa
SPL	Sound Pressure Level
ST	Strouhal number, Dimensionless
Uvc	Vena contracta velocity, m/s
Wa	Acoustic power, W
Wm	Stream power of mass flow, W
hx	Acoustic efficiency factor, Dimensionless
r	Fluid density, kg/m3
rp	Fluid density at pipe, kg/m3
rc	Fluid density at observer, kg/m3

Valve Actuators

Go to Specific Subject: Compact Valve Actuator Solutions and Systems | Subsea Valve Actuators | Offshore Valve Actuator | High Pressure Manifolds Actuators | Safety Related Systems Valve Actuator Systems | Spring Return Hydraulic Actuators | Spring Return Pneumatic Actuators | Compact Double Block & Bleed (DBB) Valve Actuators | Double Acting Actuator | Compact Actuators in Floating Liquefied Natural Gas (FLNG) Applications | Valve Actuator General Information | Scotch Yoke Design Valve Actuators | Firesafe Actuators | Valve Actuator Standards | Hydraulic Actuator Design and Operation | Electrical Actuator Design and Operation | Control Valve Actuator Design and Operation | Valve Actuator Accessories

 

Control / On - Off Valve Actuator Description

Control, On-Off Ball, Gate, Globe and Butterfly valves all require a mechanism to actually “drive” them, this is what is called an “Valve Actuator”. These Valve Actuators come in various forms, and use various power sources as an operating medium. Typically the power sources utilised by the Instrument and Control System design engineers is pneumatic, hydraulic and electrical. Of course the most basic actuator is a manual hand wheel.

Design of the Valve Actuator - The design engineer has to consider the operating conditions such as:

1. The atmosphere and potential corrosion. If the Actuator is being utilised on an Offshore Platform or FPSO then particular care must be taken in selecting the actuator body materials and internal mechanism. Particular emphasis on this should be taken on the tubing associated with pneumatic actuators or any that ‘breathe’ on the return stroke, potentially sucking in salt or corrosive air into the internal mechanism. Under this scenario a technique called closed loop breathing is used (an excellent schematic of a typical system can be found here). Selection of any accessories such as quick exhaust, solenoid valves and limit switches etc must also consider the conditions. In the Offshore Oil and Gas Industry 316SS Actuators are sometimes selected.
2. Torque requirements must be carefully considered as too little power can mean that any stiction in the valve means that the valve may stick in the cycle. Too much power may actually cause the valve mechanism to shear.
3. Pneumatic Valve actuator 0 - 100% cycle may be various pressures, control valve actuators are generally 3 - 15 psi (20 - 100kpa). However they may sometimes be set differently to this.
4. On - Off Valve Actuators may be set to other pressures, commonly 0 to 100 psi, this is to keep the size of actuator as compact as possible.
5. Hydraulic Valve Actuators utilise much higher pressures, especially on very large ball valves, this design is used to obtain the higher torques required and to keep the actuator and valve footprint as compact as possible.
6. Smart Positioners may be used both on Control and On - Off Actuator Valve combinations, these are a superb maintenance tool in that the Valve/Actuator signature at new conditions can be taken. Any changes outside parameters then mean that any maintenance is condition based.

 

ATC Valve Actuators Technical Information, White Papers and Application Details

ACT Actuators accommodate a specific market need for a compact spring return actuator to operate quarter turn and linear operated valves. Applications that particularly benefit from their compact design are those where installation space is limited, like on topsides, high-pressure manifolds, internal / external turret areas and (vertical mounted) riser valves. A compact actuator design could also benefit the handling, mounting and alignment in case large valve sizes/high pressure ratings do apply. Due to the enhanced actuator design, ATC actuators are also installed in shallow to ultra deepwater, and available complete with ROV interfacing and receptacles to ISO. ATC actuators are SIL 3 compliant to IEC 61508 and are manufactured in compliance with the ISO 9001 2000 quality procedures.

 

Compact Valve Actuator Solutions and Systems

Compact Actuator Solutions and Systems - Some comprehensive Compact Actuator Design Information and Application details from Prochem.

 

Engineering Features of the ATC Valve Actuator

• Compactness - Design flexibility, combined with the innovative integration of all actuator parts, results in the most compact actuator available in the market. In virtually all applications, irrespective of hydraulic or pneumatic supply, the ATC actuator diameter is smaller than the Face-to-Face dimension of the valve. The ATC actuator enables designers to minimize overall dimensions, reduce platform weight & deck load and ease the design of steel support structures.
• Enhanced Performance - ATC compact actuators are based on an advanced compact design with a revolutionary self-lubricating, low-friction torque conversion mechanism which eliminates the risk of any mechanical wear and tear. If the application requires an advanced level of optimization (in dimensionsor torque), the actuator output can be adapted to the exact valve torque.As a further benefit, the air or oil displacement can be reduced by up to 50%, contributing to savings in the control system, HPU or airset.
• Reliability - Due to its innovative yet simple design, the ATC compact actuator is based on a minimum number of parts. As a result, maximum reliability is ensured throughout our entire range. ATC compact actuators are hermetically sealed, airtight and watertight under all conditions. A complete FMECA has been carried out, including verification of the complete global installed base. As a result, TUV Rheinland has certified the ATC actuators to SIL 3, in accordance with IEC 61508, and field-proven Type A. In addition the ATC actuator has been tested extensively in accordance with the Shell type approval test procedure (DEP 31.40.70.30) and the API 6A PR2 procedure. These tests included extensive functional and seal testing, a compressed spring test and a dynamic load cycle test at 95% of the maximum torque for a total of 6200 cycles at temperatures ranging from minus 20C to 65C. The successful completion of these tests has been certified by an independent body.
• Cost Savings for Contractors and Operators - Contractors can benefit directly from using ATC compact actuators, both at the FEED stage and the EPC(I) stage. The number of engineering hours (e.g. for piping lay-out) has been reduced drastically on a considerable number of projects. ATC compact actuators also make it possible to cut material costs and weight thanks to an optimised and shortened piping lay-out. In addition due to the nature of the design, no specific maintenance programs are required on ATC actuators during the lifespan of your project. Consequently, ATC compact actuators result in maximum availability at lowest operational cost without requiring periodic maintenance - not even actuator replacement!

 

Subsea Valve Actuators

Subsea Actuator Technical Features - ATC has a complete line of sub-sea actuators available suitable for shallow water applications and installation in ultra deep waters, including ROV interfacing. This includes Submerged production, Submerged (off) loading, Sub Surface Isolation Valve (SSIV), PLEMS, Subsea Manifolds, Production Valves, Pipeline Valves, and Pigging Valves.

Subsea Quarter Turn

Subsea Linear

 

Offshore Valve Actuator

Topside Actuator Applications - Topsides / Manifolds, FPSO Turrets, Loading Buoys, Riser Valves, Isolation Valves, and Ballast Valves.

Upstream Quarter Turn Hydraulic

Upstream Quarter Turn Pneumatic

 

High Pressure Manifolds Actuators

Application of Compact Actuators on High Pressure Manifolds - Space and Weight are an important consideration when designing Valving and their associated actuators on High Pressure Manifold Systems. Actuators which can be installed in different angles provide significant advantages. By utilizing Compact Actuators a “minimum design footprint” can be achieved.

 

Safety Related Systems Valve Actuator Systems

Actuator for Safety Related Systems - The ATC spring return actuator offers an enhanced reliability, while having a minimum quantity of actuator parts. A complete FMECA has been carried out in conjunction with a complete review of our installed base. The actuator is certified by TUV Rheinland to meet SIL 3, following IEC 61508 and based on a 1oo1 architecture applied.

 

Spring Return Hydraulic Actuators

Spring Return Hydraulic Actuator Technical Features - The standard ATC spring return actuator is the most compact actuator available in the market. In short, the ATC actuator offers the following advantages:

 

Spring Return Pneumatic Actuators

Spring Return Pneumatic Actuators Technical Features - Due to the innovative design, The ATC pneumatic spring return actuator is available in dimensions which are close to the hydraulic version and therefore uniquely compact.

 

Compact Double Block & Bleed (DBB) Valve Actuators

Compact Double Block & Bleed (DBB) Valve Actuator Technical Features - The ultra compact ATC actuator allows for “redundant actuation” within one valve body (DBB) rather than using 2 individually installed valves. This optimisation results in a considerable reduction in pipe length, flanges, adapter sets and having the most impact in case exotic pipe materials are applied.

 

Double Acting Actuator

Double Acting Actuator Technical Features - The ATC double acting actuator is based on the same unique design approach and flexibility as applies to the spring return range.

 

Compact Actuators in Floating Liquefied Natural Gas (FLNG) Applications

FNLG Vessel Design Requires the Latest Weight and Space saving Concepts - Space and weight saving on FLNG facilities are an essential design parameter as “real estate” is very limited. Hence Compact Actuators are an important component in achieving this design goal and have been utilised in major projects around the world. Also whilst space and weight are paramount the additional savings associated with Passive Fire Protection add to the overall justification and use of these products.

 

Valve Actuator General Information

Valve Actuator - Actuators are used for the automation of industrial valves and can be found in all kinds of technical process plants: they are used in waste water treatment plants, power plants and even refineries. This is where they play a major part in automating process control. The valves to be automated vary both in design and dimension. The diameters of the valves range from a few inches to a few meters. Depending on their type of supply, the actuators may be classified as pneumatic, hydraulic, or electric actuators - This link from Wikipedia gives lots of technical information.

A Descriptive Definition of Valve Actuators - Chris Warnett - A valve actuator is any device that utilises a source of power to operate a valve. This source of power can be a human being working a manual gearbox to open or close a valve, or it can be a smart electronic device with sophisticated control and measuring devices. With the advent of micro-circuitry the trend has been for actuators to become more sophisticated. Early valve actuators were no more than a geared motor with position sensing switches. Today’s valve actuators have much more advanced capabilities. They not only act as devices for opening and closing valves, but can also check on the health and well being of a valve as well as provide predictive maintenance data - from Rotork Controls Inc and Valve World.

 

Scotch Yoke Design Valve Actuators

Scotch Yoke - The Scotch Yoke principle is characteristic for its high torque when required - at the beginning and end of each operation. This increases safety, especially in applications where the valve remains stationary throughout long periods. From Austral Powerflo Solutions and Remote Control.

Scotch Yoke or Rack-and-Pinion Pneumatic Part-turn Actuator? - Günter Öxler - This article reports on the best choice between the different technical solutions offered by pneumatic part-turn actuators - from Valve World.

 

Firesafe Actuators

Firesafe Actuators - Thanks to Samson Controls.

 

Valve Actuator Standards

EN 15714-1:2009 - Industrial valves - Actuators - Part 1: Terminology and definitions.
EN 15714-2:2009 - Industrial valves - Actuators - Part 2: Electric actuators for industrial valves - Basic requirements.
EN 15714-3:2009 - Industrial valves - Actuators - Part 3: Pneumatic part-turn actuators for industrial valves - Basic requirements.
EN 15714-4:2009 - Industrial valves - Actuators - Part 4: Hydraulic part-turn actuators for industrial valves - Basic requirements.

 

Hydraulic Actuator Design and Operation

Hydraulic Actuator Design and Operation - Pneumatic actuators are normally used to control processes requiring quick and accurate response, as they do not require a large amount of motive force. However when a large amount of force is required to operate a valve hydraulic actuators are normally used - from Engineers Edge.

 

Electrical Actuator Design and Operation

Control Valve Actuators - Their Impact on Control and Variability - Chris Warnett - Electric control valve actuators provide excellent performance and are ideal for oil and gas wells in remote production fields. Instrument air supply systems are costly and require significant energy to run. If mains power isn’t available, an instrument air supply isn’t practical, especially when only a few control valves are in use at a location. Solar powered DC electric actuators are ideal for such an application - from Rotork.

How Electric Control Valve Actuators Can Eliminate The Problems of Compressed Air as a Power Medium - Today, a new major technological advance is available that can help control-valve users avoid many of the problems and inefficiencies associated with using compressed air as a power medium. The new solution uses electric power and eliminates dependence on compressed air. This totally electric solution is appropriate and cost-effective for a wide variety of control-valve applications, including those found in such sectors as power generation, chemical, petrochemical, and most other process industries. While the new generation of electric control-valve actuators may not be suitable for all process applications, it is ideal for many situations, especially where users have experienced problems with frozen air hoses, lack of process precision, stick slip, and so on. Therefore, it is prudent for today’s process control engineers to take a serious look at how the design features of the new generation of totally electric control-valve actuators can benefit them - from Rotork.

Specification - Electric Valve Actuators in Water and Wastewater Treatment Plants - This is a typical specification from Auma Actuators, whilst product specific it is a useful basis for developing a specification.

Guidelines for the Specification of Electric Valve Actuators - This draft standard provides general requirements for the development of specifications for electric actuators - from the ISA.

General Specification for Electric Actuators - Integral Motor Control - This is a typical specification from Rotork Actuators, whilst product specific it is a useful basis for developing a specification.

 

Control Valve Actuator Design and Operation

The Fisher Control Valve Handbook - This superb 295-page PDF whitepaper is a control valve resource that has been consistently updated for 30 years. It contains vital information on control valve performance and latest technologies. Thanks to Emerson Process Management.

Control Valve Actuator Bench Set Requirements - Jerry Butz - Control Valve “Bench Set” is an often-misunderstood point of confusion, and sometimes incorrectly described part of a control valve’s actuator specifications. But not understanding it can set one up for a failure in the form of a mis-sized actuator and spring. Maybe this information can help to clear the cloud of confusion and make it easier for engineers, technicians, and operators to understand - from Flow Control.

Understanding Control Valve Bench Set - Dave Harrold-from Control Engineering.

Control Valve Actuators and Positioners - Control valves need actuators to operate. This tutorial briefly discusses the differences between electric and pneumatic actuators, the relationship between direct acting and reverse acting terminology, and how this affects a valve's controlling influence. The importance of positioners is discussed with regard to what they do and why they are required for many applications - from Spirax Sarco.

Control Valve Actuator Options - Today’s Actuators Offer Imposed Performance With Lower Life-Cycle Costs. The Challenge Is Choosing the Right One for the Application - George Ritz - Over the past several years, valve actuators have received relatively little attention while process control specialists concentrated on controllers, sensors, and other components of the control loop. This is borne out by the unglamorous nickname “pig iron” assigned to the actuator/control valve unit. With the onset of the smart-valve generation, it suddenly appears that the control valve actuator may get more respect along with its new electronics degree - from CCI.

Linear Pistion Actuators - Samy, Stemler - High Reliability of actuation is of paramount importance in the nuclear power industry. Pneumatic actuators form the largest installed base with many in safety significant applications. This paper addresses the issues related to actuation, such as available Thrust, Stiffness, Sensitivity, Hysteresis, Dead band, Dynamic Stability and a sizing example. This paper also presents comparisons between various types of linear actuators and their relative advantages and disadvantages. Also presented will be evaluation techniques for troubleshooting actuator problems and improving plant performance - from CCI.

Closed Loop Breathing - This is a technique to ensure that corrosive or saline air cannot enter the internals of the valve on the breathing side of the valve. It is very popular in the Offshore Oil and Gas Industry and on Coastal Refineries etc - thanks to Rotork for this excellent schematic.

How to Select an Actuator - Wayne Ulanski - As the process industry continues to achieve more efficient and productive plant design, plant engineers and technicians are faced, almost daily, with new equipment designs and applications. One product, a valve actuator, may be described by some as simply a black box, having an input (power supply or signal), an output (torque), and a mechanism or circuitry to operate a valve. Those who select control valves will quickly see that a variety of valve actuators are available to meet most individual or plant wide valve automation requirements. In order to make the best technical and economical choice, an engineer must know the factors that are most important for the selection of actuators for plant wide valve automation. Where the quality of a valve depends on the mechanical design, the metallurgy, and the machining, its performance in the control loop is often dictated by the actuator - from SVF Flow Controls, Inc.

Control Valve Actuators: Their Impact on Control and Variability - Chris Warnett, In a process plant, the general function of a control valve is to restrict the opening of the valve so it affects the flow or pressure of the liquid or gas that is passing through it. In any given application, an installed valve, whether it is a rotary or sliding stem valve, has one fundamental variable - the position of the moving element. That single moving element determines the exposed orifice that allows greater or lesser flow through the valve, which in turn provides the control of the process. The valve itself may be extremely sophisticated with exotic body and seat material, or it may have complex flow patterns that allow for a high pressure drop or some other function. However, the fundamental requirement to move the valve stem to position the control element remains the same regardless of whether it is a simple or a sophisticated valve. A control valve actuator is used to move the valve stem (which is attached to the internal control element) to the desired position and hold it in place. In addition to the act of moving and holding positions, there are many other parameters to that movement which determine the best type of actuator that should be used for every specific application. For example, other important considerations might include speed, repeatability, resolution, and stiffness - from Rotork Process Controls and Valve World.

 

Valve Actuator Accessories

The following links are provided by Austral Powerflo Solutions.

Rotary Limit Switch Boxes - Rotary limit switch boxes provide a visual and remote electrical indication of quarter turn valve/actuator position (ball, butterfly and plug).

Bolt Switches - "Bolt" switches are magnetic proximity switch suitable for any type of position indication.

Valve Position Indicators - The 3D Series namur indicators provide high visibility verification of valve/actuator position. The indicator features a rotor with red and green quadrants that rotate to indicate valve open and valve closed positions.

Instrument Valves and Accessories

 

Instrument Valves and Accessories are a critical part of any Instrument Hook Up. The valves and accessories include those listed below. 

Go to Specific Subject: Common Questions Associated with Instrument Valves and Accessories | Instrument Ball Valves | Instrument Bleed Valves | Instrument Check Valves | Close Coupled Mono flange and Large Bore Direct Mount Manifold | Primary Isolation Double Block and Bleed Valves | Instrument Excess Flow Valves | Instrument Gauge Valve | Instrument Hand and Gauge Valves | Micron Filters | Instrument Needle Valves | Instrument Relief Valves | Instrument Root Valves| Instrument Toggle Valves | Instrument Tubing Saddles |

 

Common Questions Associated with Instrument Valves and Accessories

What materials are used and why?

The materials generally used in producing a suitable alloy are Carbon, Silicon, Manganese, Chromium, Molybdenum, Nickel and Copper in different proportions to create different mechanical properties, such as tensile strength, depending on the conditions in which they are to be placed. That is, for example, whether the environment is corrosive, hot, wet or changeable etc.

What does NPTF thread stand for?

NPT thread stands for National Pipe Taper. It refers to the thread that tapers inward to create a better seal. It is recommended that care is taken in regards to the thread tolerances and only the best quality units are purchased to achieve this. It is imperative that any manufacturer has demonstrated quality assurance to a high standard. It is worthwhile ensuring the quality of threads by gauging at least a proportion of the threads to ensure compliance. Also it is recommended that thread tolerances and gauging should be specified to a tolerance better than the requirements of ASME B1.20.1. ICEweb's compression fittings page has a more detailed explanation of the gauging and tolerance requirements.

What does ASTM/UNS stand for?

ASTM stands for American Society for Testing and Materials.
UNS stands for Universal Numbering System.

What is an OS&Y valve?

An OS&Y valve is an Outside Screw and Yoke valve. It is a part of the piping specification. It has a firesafe outside screw construction.

Why is the Molybdenum content of 316SS 2% minimum in an offshore environment?

The molybdenum content is at a minimum 2% to prevent chloride corrosion.

Why is 303 or 304SS not to be used in an offshore environment?

303 or 304SS is not to be used because their molybdenum content is nil and thus the material is subjected to chloride corrosion.

Is there a maintenance issue when Close Coupled Monoflanges are used?

If the Monoflange is installed on a clean, non blocking process then it is not an issue in that access to the tapping point is required very rarely. This is especially so on Fieldbus and HART systems as the transmitter provides a huge amount of diagnostics on-line. The huge advantage of Close Coupling is that many instrument fittings are no longer required, thus eliminating potential leak failure points.

 

Instrument Ball Valves

General Purpose Ball Valves at a Glance - Ball valves provide a wide range of capabilities for various applications. Select a ball or trunnion valve for simple operation, visual indication of flow, full porting for maximum flow, rodability and long cycle life.

• Choose a 2-way ball valve for quick, quarter-turn, on - off service.
• A 3-way ball valve employs 180° operation for diverting flow from one line to another.
• 4-way valves are dual switching valves, changing two flow paths at the same time. 5-way, or diverter, valves allow flow through any of four possible paths.

High Cycle Ball Valves at a Glance - High Cycle ball valves are designed for repeatable, zero leakage sealing when control conditions demand valve actuation exceeding 50,000 cycles. Their unique stem- and seat designs provide packless-free operation and ease of maintenance.

Fire Safe Ball Valves - Fire Safe Valves meet demanding application requirements in the production environment of chemical and petrochemical processing facilities. These valves have been tested to and meet the requirements of API 607, 4th edition for soft seated valves. API 607 measures the ability of a closed soft-seated ball valve to retard the propagation of a fire (downstream and to atmosphere).

 

Instrument Bleed Valves

Instrument Bleed Valves - Bleed valves allow for quick, easy manual bleed-off of system pressure.

 

Instrument Check Valves

Instrument High Flow Poppet Check Valves - These Valves, recommended for severe service, including CNG applications have the following features, High Cv flow rates, Blowout-proof o-ring design, Ability to withstand high opening shocks without damage.

 

Close Coupled Mono flange and Large Bore Direct Mount Manifold

ICEweb's Monoflanges and Instrument Manifolds page has extensive technical engineering information on this subject.

 

Primary Isolation Double Block and Bleed Valves

Technical Reference on Primary Isolation Valves - This comprehensive Technical reference from Anderson and Greenwood gives excellent information on:

• Primary Isolation Valve - Primary Isolation Valve applications, advantages and disadvantages, features and benefits, Quarter Turn Ball Valve specifications, OS&Y Needle Type Globe Valve Specifications, HD Needle Type Globe Valve Specifications, along with a comparison with more traditional valve hookups.
• Double Block and Bleed Valves - These valves are integrally forged, one-piece double block and bleed assemblies for primary isolation of pressure take-offs, where the valve is directly mounted to the vessel or process pipe. Instruments may be directly mounted to the valve outlet or alternatively remotely mounted with gauge lines/impulse pipe work.
• Unique Series of Optional End Connections - This bulletin feature a unique series of really smart optional end connections which can be bolted onto the valve outlet in place of the standard 1/2-inch NPT female threaded connection. Bolt on connections are available as: Instrument Kidney Flange / Welded Connection / Dual Threaded Connection.
• Enhanced Locking Security of Instrument Valves - Ball valve locking handle provides additional security against tampering or accidental loosening as a result of vibration or physical damage. Allows the valve to be locked open or closed.
• Quill for chemical injection and sampling service - designed to ensure high pressure media can be injected into the optimum position of the flow stream through the process pipe work. It also enables clean product samples to be removed from the main flow. Includes details on Sour Gas Materials, Integral Check Valves and Low Temperature service versions.
• Monoflanges - also see ICEweb's Monoflange and Instrument Manifold page.
• Root Valves - An integrally forged one-piece block and bleed assembly for primary isolation of pressure take-offs, where the valve is either screwed or welded directly into the vessel or process pipe without the need for a flanged connection. Instruments may be directly mounted to the valve outlet or alternatively remotely mounted with gauge lines/impulse pipe work.

 

Instrument Excess Flow Valves

Excess Flow Valves - These valves act as flow switches that automatically close when a flow spike occurs, preventing uncontrolled release of system fluid. They are available in automatic and manual reset versions, depending on system requirements. Automatic reset versions can have an “anti-clog” wire which increases reliability by preventing a build up of system fluid in the bleed port. Others are high pressure (0 to 6000 psig [414 bar]), high performance, quick acting, zero leakage, low maintenance excess flow valves that will help provide a reliable and safe working environment.

 

Instrument Gauge Valves

Technical Reference On Gauge Valves - This comprehensive Technical reference from Prochem Pipeline products gives excellent information on:

• Bonnet Technology - Covering both soft and hard seat, mini bonnet assembly, arctic low temperature applications.
• Block and Bleed - Static pressure gauge and instrument installation for isolation and venting.
• Multi-Port Gauge Valves - These valves allow the versatile positioning of gauges or pressure switches without requiring additional penetration of the main piping.
• OS&Y Root Valves-Root Isolation Valves with Outside Screw and Yoke, Bolted Bonnet Construction - This is a multi-ported OS&Y root/primary instrument isolation valve, designed for use with gauge mountings and other pressure instruments in refineries and chemical plants. It facilitates installation of multiple measurement devices without additional penetrations of the main piping.
• Gauge Valve Accessories:

  Bleed Tee - A Bleed Tee is a single male inlet, triple female outlet piping tee. It is generally used with the process root valve to simplify downstream piping and reduce the number of potential leak points. The Bleed Tee can be used with any 1/2-inch or 3/4-inch valve in an instrument piping system and allows either vertical or horizontal pressure gauge mounting. As an option, a bleed plug (as shown above) can be assembled into the tee to provide a means of relieving pressure for maintenance purposes.

  Bleed Plug - The bleed plug provides an economic means to bleed process pressure trapped between the Valve and instrument. This bleeder valve vents to atmosphere and has bubble-tight shutoff.

  Seat Resurfacing Tool - The flow of abrasive fluids may, over time, score the seating surface of the valve body. The seat resurfacing tool will re-machine this surface and allow the valve to once again deliver bubble-tight shutoff.

  Bonnet Lock (patent protected) - The Bonnet Lock (BL) prevents accidental loosening of the bonnet-to-body seal, and is a low-cost alternative to a union bonnet. A high-strength short bonnet pin aligns a hex collar over the bonnet. A standard SS hollow-point set-screw or lock nut locks the collar against the bonnet. Tests indicate that the minimum torque required to break the collar loose is greater than the torque required to twist off the valve stem.

  Gauge Adapters - Designed for use with any gauge valve to increase site versatility, the GA swivel gauge adapter allows positioning of pressure gauges in any direction through 360 degrees via a compression fitting.

  Gauge Syphons - Designed to replace the old pigtail type of siphon, this accessory provides a thermal barrier between hot vapours and the pressure instrument. It reduces the amount of potential gauge whip on vibrating lines by bringing the gauge closer to the process connection.

 

Instrument Hand and Gauge Valves

Hand and Gauge Valves - These include multi-port and block and bleed styles suitable for gauge isolation, calibration and venting with a choice of either globe pattern or through-bore designs. A wide choice of end connections and comprehensive range of standard gauge accessories allows complete flexibility for individual installations - From Prochem Pipeline products.

 

Micron Filters

Micron Filters - With a Variety of Micron Filtering ranges from 2 to 55µ these units have applications such as trapping foreign particles, protecting sensitive equipment, system purging and acting as a pressure damper, see page 27.

 

Instrument Needle Valves

Needle Valves at a Glance - This technical bulletin covers a complete line of precision needle valves. Before making your valve selection, be sure to consider the system pressure, operating temperature, required flow and materials of construction. It also details the following:

• Design of Stem packing - Provides superior sealing performance while reducing maintenance costs. Consisting of alternate wafers of TFE and metal spacers, stem leakage is virtually eliminated while the problems associated with TFE cold flow are minimized.
• Choice of Stem Tip Options to Provide Greater Flexibility:

  Blunt Vee-Point - The blunt vee-point stem tip provides full flow with only a few turns of the valve handle.

  Vee-Point - The vee-point stem tip is used to provide leak-tight shutoff in small orifice valves.

  Regulating - The regulating stem tip has a gradually tapered tip which allows for greater control of flow.

  Non-rotating Metal Stem Tip - A non-rotating stem tip is typically used in high cycle applications to extend the service life of the valve. Its purpose is to prevent galling in the seat and on the stem tip. As the valve is closed, the stem tip contacts the valve seat, and is driven straight into it without rotating.

  Vee-Point - The vee-point stem tip is used to provide leak-tight shutoff in small orifice valves.

  PCTFE - A PCTFE stem tip requires a lower seating torque than a metal stem tip. It will provide full flow through the valve with only a few handle turns. The PCTFE tip is replaceable and has a maximum temperature of +250^° F (+121^° C).

  Non-rotating PCTFE Stem Tip - A non-rotating PCTFE stem tip operates in the same fashion as the non-rotating metal stem tip but requires less seating torque.

• Flow capacity of HOKE Needle Valves - The Cv factor is a flow coefficient expressing the rate of flow in gallons per minute of 60^° F (16^° C) water with a pressure drop of 1 psi across the valve. The flow is dependent on the inlet and outlet pressures, temperature, specific gravity and the Cv coefficient. Both liquid and gas calculations are detailed.
• Severe Service Needle Valves - details on a valve for steam and other severe service applications.
• Sour Gas Service Needle Valves.

 

Instrument Relief Valves

Right Angle Instrument Relief Valves - These valves provide users with high accuracy and consistency of cracking and reseat pressures. Furthermore, narrow pressure ranges (cracking pressures) for each model can be factory pre-set according to customer specifications. PED certification and CE marking are standard for all models.

 

Instrument Root Valves

Root Valves - These valves are an integrally forged one-piece double block and bleed assembly for primary isolation of pressure take-offs where the valve is either screwed or welded directly into the vessel or process pipe without the need for a flanged connection. Instruments may be directly mounted to the valve outlet or alternatively remotely mounted with gauge lines/impulse pipe work.

 

Instrument Toggle Valves

Instrument Toggle Valves - Featuring a simple, reliable design concept, this low-maintenance valve is well suited for a wide variety of applications. The toggle handle provides easy on-off operation and visual indication of flow.

 

Instrument Tubing Saddles

Complete Tubing Control with Stainless Steel Saddles - Features 316 Marine Grade Stainless Steel, Weather and Corrosion resistant, 18g reinforced rib for added strength for sizes up to and including 12.7mm (1/2”) and Manufactured to precision tube tolerances.