Instrument Compression Fittings

Jump to the Various Sections of this and other Instrument Fittings and Tubing Pages: Achieving Optimal Results | Pressure Ratings | Assembly | Metric and Imperial Fittings | Thread Types | Gauging External Taper Threads | Gauging Internal Threads | BSP (British Standard Pipe) (ISO228) Parallel | Mixing BSP/NPT and any other Thread Standard | Making up NPT Connections | Use of Thread Tape | Thread Gauges - Use and Handling | Technical Information on Instrument Tubing and Fittings | Codes and Standards | Excess Flow Valves | Instrument Fittings Technical Data | Instrument Manifolds, Monoflanges,Valves and Accessories | Tubing Selection | Prochem Pipeline Products |


Achieving Optimum Results

  • Select fittings to match the tubing diameter and pipe thread size.
  • Fittings must be handled correctly.
  • Assemble fittings correctly to manufacturer's installation instructions and ensure all components are compatible (from the same manufacturer).


Pressure Ratings

Ensure fittings are rated to the Maximum Allowable Working Pressure (MAWP) of the tubing.



Compression fittings are supplied assembled.  The fitting, pipe thread and general appearance should be inspected visually before use.  It is recommended that fittings are not disassembled. However nuts and ferrules should be checked for correct assembly.


Metric and Imperial Fittings

Compression fittings are supplied in either Metric or Imperial tube sizes.  It is very important that types are not mixed or used on the incorrect tubing.


Thread Types

There are several common thread configurations,  in instrumentation design two types are commonally utilised.

NPT (National Pipe Tapered) threads such as Pipe Threads General Purpose (inch) conforming to ASME B1.20.1

These threads use the “interference” principle and the use of thread tape or other thread sealant is essential.  The thread tape will stop leaks via the gaps in the thread and avoid galling of the threads by giving lubrication.

Caution: In ICEWEB's opinion care should be taken on higher pressures to ensure the tolerance is better than the requirements of ASME B1.20.1 as if the male and female threads are to the outside of the tolerance then only 1.5 threads will be engaged or alternately the fittings may “bottom out”.  In both cases there are potential for blowout.  How many times have you seen this scenario?  Whilst the 1.5 threads in itself will contain most pressures without blowout it is quite possible that the Instrument Fitter will gall the threads because of insufficient thread entry.

The recommendation is NPT threads are designed to meet the dimensional requirements stated in ASME B1.20.1-1993 with the following modifications,  this will ensure that if both the fitting and the mating instrument get a 4 to 6 thread engagement. 

It is important to specify the revised tolerance on the instrument as well,  particularly on high pressure connections on equipment which are designed for noxious or hydrocarbon fluids.

The L1 thread gauging requirement in sections 8.1 and 8.2 modified to:


Gauging External Taper Threads with Ring Gauge (Male Threads)

When hand tight the male fitting must engage into the ring gauge + 1/4 to + 1 turn more than the start of the first scratch mark on the chamfer zone.


Gauging Internal Threads with Plug Gauge (Female Threads)

When hand tight the plug gauge must engage into the female fitting + 1/4 to + 1 turn below the last thread scratch on the chamfer zone.


BSP (British Standard Pipe) (ISO228)  Parallel

This type of thread utilises a washer/gasket or O-ring to achieve a seal.  It is important that any fitting also is fitted with a pin lock arrangement so that the fitting cannot vibrate loose.


Mixing BSP/NPT and any other Thread Standard on a Facility

It is highly recommended that no mixing of thread types occur on a facility.  If this culture exists it is possible for example that a Parallel thread is installed into a Tapered thread.  Thus, potential for blowout is large.


Making Up NPT Connections

Engage the threads hand tight - minimum of 4 and a maximum of 6.

An additional 0.5-1.5 turns can be expected with wrench tightness using a quality thread tape.

Hand tight engagement should be checked before applying any thread tape.


Use of Thread Tape

Thread tape should always be utilised on NPT threads,  however never on the compression fittings themselves.  Any tape should be high quality and NOT obtained from the local hardware store. A good rule is to obtain thread tape that meets the requirements of UL 340-M1979 (AGA) 3226, MIL-T-27730A or AG208.  There are thread tapes that are specifically designed for 316ss and other fittings.

There are liquid type sealants available,  these should be selected based on their specification and any anti-galling features. These sealants are particularly useful for hydraulic or clean services where small particles of tape could contaminate valves, ports etc.

Making up a Fitting when Utilising Thread Tape

  • Initially ensure that the hand-tight joint assembly gives 4 to 6 full turns of engagement.
  • Unscrew the joint, cleaning any dirt on the threads and then apply tape to the male thread.  Begin with the first thread in direction of the pitch ensuring the tape is wrapped with a slight overlap.
  • Check that the tape does not overhang the first thread, as small portions of tape may be cut off and enter the tubing system. 
  • Tension the tape but do not stretch or thin it out.
  • Cut the tape and draw the free end around the threads tautly.
  • Rub the tape onto the thread ensuring engagement with it.  In the case of stainless steel fittings, apply a second layer of tape.
  • Re-assemble hand-tight and make wrench tight with REASONABLE FORCE only to achieve another 0.5 to 1.5 turns. Please note excessive force may damage the fitting.  Teflon provides lubrication which will aid deformation or collapse of fittings if excessive force is used.  Teflon can also exacerbate loosening of slack joints.
  • When it is necessary to break and remake connections ensure that any old tape residues are removed from the threads.


Thread Gauges - Use and Handling

  • Use hand tight pressure only when gauging fittings with precision thread gauges. Do not use gauges where any rust, swarf or dirt is present in the thread. Threads must be clean and bright.   If the fitting cannot be cleaned, discard it.
  • When checking NPT threads with secondary gauges ensure that a hand tight engagement allows the leading thread of the fitting to fall between the two gauging benchmarks.
  • Do not screw any thread gauges together.  Thread gauges are precision instruments.  Engagement will cause wear and possibly dry seizure in storage.
  • When not in use, gauges should be kept clean and in their protective case.  It is good practice to apply a smear of Vaseline (petroleum jelly) to gauges in storage.

Primary Thread Gauges

Primary gauges are intended to be used as a master set with which regular comparative checks of secondary gauges can be made against a series of fittings.

Secondary Thread Gauges (L1 Standard)

Secondary gauges are intended for field use.  They must be regularly checked against primary gauges for wear and damage.

Testing Frequency for Thread Gauges

Frequency of testing secondary gauges depends on the frequency of use.  Testing is required after impact damage and chipping.  It is recommended that Primary gauges and secondary gauges are checked every six months by profile graph inspection.

NPT Standards Applicable to Thread Gauges

Primary master gauges and secondary working gauges should be manufactured and supplied in accordance with ASME B1.20.1-1993 specifications.

Correct Makeup Gauges

These gauges are product specific and give indication whether the make up is correct.  It is suggested that you contact your supplier to determine whether they are available for the product.  


Just click on the super ICEweb links below for more Technical Information on Instrument Tubing and Fittings.


Analytical, Instrumentation and Mechanical Heat Tracing and Tube Bundles - A Tubing Bundle consists of a small diameter tube or group of tubes packaged in an insulated, weatherproofed jacket. It may be steam or electric traced to provide freeze protection or temperature maintenance. Tubing Bundles are used in Instrument hook-up and impulse lines, Analyser sample transport, Insulated Tubing and Jacketed Tubing. This page provides many relevant  free technical references to Analytical, Instrumentation and Mechanical Heat Tracing and Tube Bundles.


Codes and Standards - A useful list of Instrument Fitting and Tubing Codes and Standards.


Excess Flow Valves - These devices are a real "Safety Boost" in that they limit flow in the event of a rupture.


Instrument Fittings Technical Data - This is a page which has a vast amount of Technical Engineering Information on Instrument Fittings and Tubing.


Instrument Manifolds, Monoflanges, Valves and Accessories - Information on what is a great addition to an Instrument Engineers Instrument take-off design engineering arsenal. Saving potential "failure points" means enhanced safety!


Tubing Selection - Instrument Tubing has to treated with "Respect" in that there are many facets of any design of tubing systems. This page goes into great detail with many tips.

Other Links

Fittings and Small Bore Tubing Systems - Handbook

This superb 72 page document from the Norwegian Oil and Gas Association covers most engineering aspects of small bore tubing and fittings. 

Tube and Tube Fittings - This open source book Lessons in Industrial Instrumentation by Tony R. Kuphaldt has a useful section on instrument connections has a useful section on Instrument Tube Fittings - go to page 573. This is a fantastic resource but be prepared for the 50Mbit download!


Instrumentation - Includes information on; 

  • Anderson Greenwood
  • ATKOMATIC Solenoid Valves
  • BuTech Pressure Systems - System components are available in every imaginable alloy to handle pressures form vacuum to 150,000 PSI (10,000 bar) in tube and pipe sizes from 1/8" to 1" and temperatures from -423°F (-253°C) to over 1200°F (649°C). Suitable for extreme application of erosive or corrosive solids, liquids or gases.
  • Circor Tech
  • Circle Seal
  • Classic Filters - These filters are suitable for a variety of gas and liquid applications and are used in a wide range of industries around the world. The disposable microfibre filter elements are extremely efficient as well as being low cost. There are a number of benefits with this type of element and they offer high flow rates with very low pressure drops.
  • DOPAK® Sampling Systems - Due to the growing complexity of the industrial processes in general and more specific for processes in the (petro)chemical and pharmaceutical industries, the need for tests and analyses increases continuously. The need for representative samples plays a critical role in ensuring product verification. Yet sampling directly from the process often includes the risk of exposure to the operator, as well as contamination and pollution to the environment. The Manual Sample Systems method reduces such risks with its patented design and simple method of operation.
  • GO Regulator®
  • GYROLOK® Twin Ferrule Tube Fittings
  • HOKE® Instrumentation Valves
  • King Instrument Company  - King Instrument Company offers a comprehensive line of variable area flow metres including acrylic, polysulfone, glass and metal tube metres. Optional alarms and 4-20 mA transmitter available on selected models. See more technical information on ICEweb's Flow page.
  • Leak-Check
  • Prochem NPT Ball Valves - Full Bore 2-piece threaded valves allowing straight-through flow. Virtually no head loss and a superior performer with mildly abrasive as well as corrosive fluids. Ideal for in-line control of process fluids.
  • Saddles
  • Stainless Steel Braided Hoses - Teflon® Lined
  • Stainless Steel Tube
  • Thread Tape & Thread Paste
  • Tooling
  • HOKE® Pipe Fittings

Hydraulic - Includes information on; 

  • Tube-Mac Piping Technologies
  • Tube-Mac - PYPLOK System
  • Tube-Mac Non-welded Flange Connections
  • Seamless Steel Tubes
  • PYPLOK Tooling
  • Stainless Steel Ball Valves - Hydraulic
  • Stainless Steel JIC Fittings - JIC Fittings and Adaptors provide a straightforward, positive, mechanical seal. They have been used for many years for reliable sealing in commercial, industrial and military applications. They are proven to supply dependable, reusable connections under a wide range of operating conditions including extremes of vibration, temperature and shock.

Valves and Actuators - Includes information on;

  • Prochem Actuated Valve Packages -  Specialising in Poyam, ATC, BSM, Pacson and Habonim - Prochem can deliver actuated valves in any combination to suit your valve, actuator and control system specification.
  • AMPO Poyam Valves - These are high-technology valves with best performance and low maintenance costs. Applications include Cryogenic Service, High Pressure, General Service, Metal Seated and Special Application.
  • BSM Valving Solutions - Emergency Fast Track Valve Producers and Delivery Specialists, providing Ultra fast deliveries.  Hard to obtain valves need specialist engineering.  These valves are manufactured  in a wide range of exotic materials to tight specifications..
  • ATC Actuators - The heart of the ATC actuator design is the revolutionary torque conversion mechanism combined with the integrated actuator spring. The simple operating principle offers a combination of high efficiency and small displacement, thereby creating greater design flexibility and improved reliability. This 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.
  • Pacson Valves - These are high integrity valves specifically designed for the Oil and Gas Industry.
  • Anderson Greenwood Primary Isolation Valves - Anderson Greenwood Instrumentation Products provide the ultimate solutions for a compact range of forged body Primary Isolation Valves, featuring a choice of end connections, body styles and valve technology.
  • Habonim Industrial Valves and Actuators - Habonim’s new series of ZERO-Stem-Leak valves, is based on the HermetiX™ technology. HermetiX™ is a patented stem seal designed to reduce stem leaks to a minimum and to provide maintenance-free service.

Manufacturing - Includes information on; 

  • Quality Management System
  • Fully Traceable and Complying Threads
  • Leaders in Thread Manufacture
  • Exotic Alloys
  • Engineered Solutions
  • World Class Manufacturing
  • Safety, Integrity and Reliability
  • Special Service
  • Standard Products - BSP Fittings
  • Standard Products - NPT Fittings
  • Standard Products - Other

Piping Products - Includes information on; 

  • Branch Fittings - Details on a  range of Buttweld, Socketweld, Threaded and Flanged reinforced branch fittings from 8 (1/4") NB upwards.
  • BSP Fittings - Prochem manufactures a complete range (from 6 (1/8") - 100 (4") NB) of BSP tapered, BSP parallel and BSP fastening and sealing threads for a variety of applications, in class 150 and 3000. All our BSP threaded fittings are checked with calibrated gauges during manufacture. Each batch is further confirmed as being in compliance with the international standard and before they are released into the market, all products undergo a final visual and dimensional inspection by thread profiling.
  • Buttweld Fittings - Concentric and eccentric reducers, equal and reducing tees, 45° and 90° elbows, buttweld caps and stub ends, are all part of the comprehensive range of buttweld fittings carried by Prochem.
  • Duplex Stainless Steels -  Duplex Stainless Steels are unlike the 300 (Austenitic) and 400 (Ferritic) series of stainless steels in that they have a structure consisting of approximately equal amounts of both ferrite and austenite. Therefore, they are often referred to as ferritic-austenitic stainless steels. With a chromium content ranging from 18 to 28 percent, they have improved passivity compared to standard grades. The nickel content ranges from 4.5 to 8 percent which is insufficient to promote a complete austenitic crystal structure, hence the mixed ferrite-austenite structure. Most grades contain molybdenum in the range of 2.5 to 4 percent plus small amounts of nitrogen - enhancing both strength and pitting resistance.
  • Flanges - A flange is designed to connect sections of pipe, or to join a pipe to an assembly such as a pressure vessel, valve or pump. Flanges are joined by bolting, and sealing is completed with the use of gaskets, and fixed to the piping system by welding or threading.
  • Heat Exchanger, Condensor & Boiling Tubes - Useful technical datasheet.
  • Hygienic and Tube - Prochem is well established as a supplier to the food industry. A comprehensive range of BSM, Tri-clover and buttweld fittings and valves are available throughout Australia, complete with welded and annealed polished tubes to suit. 
  • NPT Fittings - NPT fittings are designed for high-pressure (class 3000 - class 6000) applications, and have a distinctive profile for maximum strength. All NPT products are checked with calibrated gauges during the manufacturing process and each batch is further confirmed as being in compliance with the international thread standard. Before they are released into the market, each item is subject to a final visual and dimensional inspection by thread profiling. Materials used comply with ASTM A403 or A182.
  • Pipe Nipples - Pipe nipples are available in ASTM A403 WP316/316L or 304/304L materials, from 6 (1/8?) NB upwards, threaded BSP or NPT, bevelled or plain ended. Prochem has the ability to manufacture pipe nipples up to 6000 mm (6 m) in length in sizes 6 NB to 80 NB.
  • Saflok Self-Locking Quick Coupler Range - Prochem provides the safest quick couplers on the market from Saflok. Included the patented locking cam arm, the Saflok design has no peer among other quick couplings.
  • Socketweld Fittings - Prochem manufactures and supplies an extensive range of the highest quality Socketweld fittings, all thoroughly inspected to ensure complete dimensional compatibility with the requirements of the ASME B16.11 manufacturing standards.
  • Swage and Pipe Nipples - Prochem manufactures, stocks and supplies a range of plain, bevelled and threaded concentric and eccentric swage nipples, from 8 (1/4") NB through to 100 (4") NB, with other sizes available on request. All swage nipples are either manufactured from seamless pipe or bar material and have an available working pressure equivavlent to straight seamless pipe. These fittings are available in ASTM A403 WP316/316L or 304/304L materials with other materials available on request.
  • Stainless Steel Shim - Grade 316 shim, annealed and with a hardness rating of HV200, is available in coiled 305 mm (12?) wide rolls, in various thicknesses and sold by the linear metre.
  • Stainless Water Solutions Package - With increased height of buildings, pressures, and life time expectations, people are turning to Stainless Steel for their Water Solutions. These pipe and fittings bear the Water Mark logo ensuring compliance to the industry specifications. Coupled with roll grooving, Prochem has the complete package to offer your Water Solutions package. All designers, architects and builders should contact Prochem to see how we can save you money!!
  • Swing and Spring Check Valves


Welded Duplex Tube - Welded Duplex Tube to: ASTM SA789/A789 UNS S31803/S32205.
Y-Type Strainer

More Information Again some great information here. This Swagelok link has considerable technical information.  It is however difficult to navigate to,  when on the main page enter as a guest or register,  go to “fittings tube” and then click on “connects tubing to tubing” and then click on any product and you will be into the technical information area.

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