Orifice Plates

Orifice Plate - An orifice plate is a device used for measuring flow rate, for reducing pressure or for restricting flow (in the latter two cases it is often called a restriction plate). Either a volumetric or mass flow rate may be determined, depending on the calculation associated with the orifice plate. It uses the same principle as a Venturi nozzle, namely Bernoulli's principle which states that there is a relationship between the pressure of the fluid and the velocity of the fluid. When the velocity increases, the pressure decreases and vice versa. This technical information from Wikipedia, the free encyclopedia gives a good overview.

Good Practice Guide an Introduction to Differential Pressure Flow Meters - This introductory guide to differential-pressure (Δp) flow meters has been produced for people who are relatively inexperienced in using this type of meter or who would just like to learn more about the subject. The guide provides useful information on the maintenance of existing meters and for purchasing a new metering system. The introduction covers the basic theory of how differential-pressure flow meters work and fundamental background information. Some of the most common types of meters are described together with their advantages and disadvantages. This includes orifice plates, Venturi tubes, cone meters, nozzles, variable area meters and averaging pitots. Practical information and guidance are provided on the use of differential-pressure meters including important considerations for the selection and ongoing maintenance of a suitable meter. A useful table on the advantages and disadvantages of a more extensive range of differential-pressure meters is provided in the summary. By reading this guide you will not become an expert in differential-pressure meters, but it will give you some useful and practical information on their use - from the National Measurement System.

Orifice Plates - The Engineering Toolbox has a a useful range of technical pages on many aspects of Orifice Plates.

Differential Pressure Orifice - The most commonly used flowmeter is the orifice meter. The orifice meter consists of two parts. These are the measurement orifice plate, which is installed in the process line, and the differential pressure transmitter, which measures the pressure developed across the orifice plate. There has been extensive research to determine the operating characteristics of orifice meters. The physical phenomenon of the orifice meter is described by the Continuity equation and the Bernoulli equation - from Gilson Eng.

Fundamentals of Orifice Metering - Throughout the oil and gas industry, there stems the need for accurate, economical measurement of process fluids. Orifice metering satisfies most flow measurement applications and is the most common flow meter in use today. The orifice meter, sometimes called the head loss flow meter, is chosen most frequently because of its long history of use in many applications, versatility, and low cost, as compared to other flow meter available - from the Acadiana Flow Measurement Society.

Conditioning Orifice Plate Technology; Taking the Standard to a New Level of Capability - A very interesting article from Emerson Process Management which highlights the advantages of this innovative design which enables multiple benefits without compromising performance.

Fundamentals of Orifice Meter Measurement - An orifice meter is a conduit and a restriction to create a pressure drop. An hour glass is a form of orifice. A nozzle, venturi or thin sharp edged orifice can be used as the flow restriction. In order to use any of these devices for measurement it is necessary to empirically calibrate them. That is, pass a known volume through the meter and note the reading in order to provide a standard for measuring other quantities. Due to the ease of duplicating and the simple construction, the thin sharp edged orifice has been adopted as a standard and extensive calibration work has been done so that it is widely accepted as a standard means of measuring fluids - from Emerson Process Management.

Application of the Orifice Meter for Accurate Gas Flow Measurement - The most common device used in gas flow measurement is the orifice flow meter. It is capable of very accurate measurement provided it is properly applied, designed, installed, maintained and interpreted. It is the intention of this article to cover these aspects of the orifice meter so that the use of the device can be evaluated and a proper decision made on application - from Emerson Process Management.

Orifice Plates, Orifice Flanges, Metering Runs and Venturi Tubes – This very useful engineering document from ABB covers Orifice Plates, their Maintenance, Inspection, Assemblies, Metering Runs and more.

Orifice Flowmeter Calculator - A fluid passing though an orifice constriction will experience a drop in pressure across the orifice. This change can be used to measure the flowrate of the fluid. To calculate the flowrate of a fluid passing through an orifice plate, enter the parameters into the table. (The default calculation involves air passing through a medium-sized orifice in a 4" pipe, with answers rounded to 3 significant figures.) - from efunda.

Sizing Orifice Plates - Meeting Modern Expectations - Allan G. Kern - Orifice plates with differential pressure (DP) transmitters remain the workhorses of fluid flow measurement in the process industries, due to their proven robustness, ease of use, adaptability to a broad spectrum of applications, familiarity, and economy. The weak side of orifice plates, where otherwise properly applied and installed, is limited turndown, with a nonlinear loss of accuracy at lower flow rates due to the square-root nature of the flow/DP relationship.When sizing orifice plates, some new rules of thumb can be applied to significantly improve orifice plate turndown and accuracy, while gaining extended measurement range, in most applications. This can be accomplished for the cost and effort of revising the calculation, buying a new orifice plate, and re-configuring the transmitter, activities that are routinely carried out in any case - from InTech and the ISA.

Development of Orifice Meter Standards - This paper is for the purpose of reviewing how we have arrived at the orifice meter standards, what is their value and what we can expect in the future. It is of value to review this background since respect for the orifice standards (and other standards) has diminished. This can lead to real chaos for the gas industry. The last way you want to solve your measurement problems is based on personal opinions – this is the purpose of the standards, because it represents consensus data with legal standing - from Emerson Process Management.

Orifice Plates for Flow Measurement & Flow Restriction - This document covers the basics of orifice plates - from wermac.org.

Theoretical Uncertainty of Orifice Flow Measurement - Orifice meters are the most common meters used for fluid flow measurement, especially for measuring hydrocarbons. Meters are rugged, mechanically simple, and well suited for field use under extreme weather conditions. In 1779, an Italian physicist named Giovanni B. Venturi (1746-1822) performed the first recorded work that used orifices for the measurement of fluid flow. Many years of field experience with wide range of meter sizes, variety of fluids, and numerous investigative tests have identified all major contributing factors of measurement uncertainty of orifice flowmeters. Because of their long history of use and dominance in the fluid flow measurement, their designs, installation requirements, and equations for flow rate calculation have been standardized by different organizations in the United States and internationally [Ref 1-7]. These standards provide the guideline for the users to achieve accurate flow measurement and minimize measurement uncertainty. This paper discusses different factors that contribute to the measurement inaccuracy and provide an awareness to minimize or eliminate these errors - from Emerson Process Management.

Orifice Meter Station Operation & Maintenance – A video giving the basics.

VIDEO - Back to Basics: DP Flow Measurement - Walt Boyes - Part One-- Differential Pressure Flow Measurement.

The following information from the CEESI technical library whilst being old covers many fundamentals very well.

• Effects Of Abnormal Conditions Of Orifice Meters - Zaki D. Husain - The orifice meter has been a standard in the gas industry for years. With proper operation and maintenance, the orifice meter has proven to be an accurate method to measure natural gas. The orifice meter is one of the most basic devices ever invented for measurement However, it also has associated problems as a result of its simplicity. With the increasing demand and prices of natural gas minimizing error in measurement has become essential.
• Effects of Abnormal Conditions on the Accuracy of Orifice Measurement - Bill Johansen - The effects of abnormal conditions on orifice plate based flow measurement is a broad topic. The research on abnormal effects has typically focused on issues such as the effects of bent plates, plate eccentricity, dulled orifice bore leading edge, the presence of water and liquified hydrocarbons, and many other conditions found in pipeline orifice meters. This paper discusses potential problems in four areas of orifice based flow measurement: calculation of discharge coefficients, calculation of expansion factors, flow conditioning, and gas sampling.
• Effects of Entrained Liquid on Orifice Measurement- Bill Johansen - Natural gas often has some liquid content. The liquid may be water, hydrocarbons, or compressor oil. As this gas flows through an orifice meter is the gas being measured correctly? This paper discusses four test programs that were conducted to examine the effects of entrained liquids on orifice meter performance.
• The Effects of Oil Coating on the Measurement of Gas Flow Using Sharp Edged Orifice Flowmeters - Bill Johansen and Tom Kegel - Orifice plates are known to be sensitive to a variety of effects due to dimensional variations and flowing fluid conditions. A number of studies have been performed to determine the specific effects of water entrainment and two phase flow on orifices, but the results were not well documented and were limited in scope. This paper describes an investigation funded by the Gas Research Institute (GRI) to determine the effects of a coating of compressor oil on the flowmetering performance of orifice plates. A viscous oil is used to coat only the plate or both the plate and upstream piping. The effect of this coating on orifices having different diameter ratios (B) in several different line sizes is evaluated by statistically comparing the discharge coefficient for the wetted orifice to the discharge coefficient when dry.
• Effect of Liquid Entrainment on the Accuracy of Orifice Meters for Gas Flow Measurement - V.C. Ting and G. P. Corpron - This paper presents the results of a study to show that a small amount of liquid entrainment in an orifice meter can affect the accuracy of gas flow measurement.
• The Orifice Expansion Correction for a 50 mm Line Size at Various Diameter Ratios - Walt Seidl - The expansion coeffiecient or factor for a compressible flowmeter corrects for the change in pressure and density as the fluid is accelerated through the flowmeter. This paper describes the results of a test program to determine the expansion factors for flange-tapped sharp-edged orifices with diameter ratios between 0.242 and 0.726 in a nominal 50 mm (2 inch) line.
• Effects of Abnormal Conditions on the Accuracy of Orifice Measurements - Steve Caldwell - The orifice meter is one of the most widely utilized measurement devices and is one of he oldest, next to the bucket. The orifice meter is one of the most basic devices ever invented for measurement and has many advantages because of its simplicity and also has many associated problems as a result of its simplicity.
• Effects of Abnormal Conditions on the Accuracy of Orifice Measurements - Taft Snowdon - The orifice meter remains the foremost measurement device used on the industry for hydrocarbon flow. The primary element of the orifice meter is the orifice plate and orifice meter tube consisting of the orifice fitting, or flanged pressure taps, adjacent piping and the flow conditioner or straightening vanes. The complete system also includes the temperature and pressure measuring devices used often called the secondary element and the pressure lines from the taps to the pressure instruments. The American National Standard Institute/American Petroleum Institute Standard 2530 (ANSI/API 2530) also called the AGA-3, provides specific recommendations for the manufacture, inspection and installation of an orifice meter. In order to ensure accuracy, with minimum uncertainty, these guidelines and inspection procedure should be established by taking relatively fundamental measurements of the primary element components.
• New Data for the Quadrant Edged Orifice - Charles Britton and Steve Stark - New experimental data is presented for both quadrant-edge and sharp-edge orifice plates used in low Reynolds number applications - from starkassoc.com.
• Effects of Abnormal Conditions on the Accuracy of Orifice Measurements - Steve Caldwell.

Orifice Plate Standards

ISO 5167-2:2003 - Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full - Part 2: Orifice plates.

AGA 3.1 Orifice Metering of Natural Gas and Other Related Hydrocarbon Fluids Part 1-General Equations and Uncertainty Guidelines - This standard provides a single reference for engineering equations, uncertainty estimations, construction and installation requirements, and standardized implementation recommendations for the calculation of flow rate through concentric, square-edged, flange-tapped orifice meters. Both U.S. customary (IP) and International System of Units (SI) units are included - from Law Resource.Com.

Flow Measurement User Manual - This manual discusses gas flow measurement based on philosophies expressed in AGA (American Gas Association) and API (American Petroleum Institute) guidelines. It has some useful information on Orifice Plates and the relevant standards - - from Emerson Process Management.