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Jump to the Various Sections of this and other Instrument Fittings and Tubing Pages; Instrument Tubing Selection | Instrument Tubing PreparationInstrument Tubing for Hazardous Gas Service | Instrument Tube Bending | Minimum Straight Lengths | Fitting Preparations | Tubing Installation | Supporting Tubing | Instrument Tubing Welding | Plastic Instrument Tubing | Instrument Tubing Data Charts |Training | Instrument Tubing Links | Instrument Tubing and Fittings Manual | Technical Information on Instrument Tubing and Fittings | Prochem Pipeline Products | Other Links | Instrument Fittings Technical Data | Codes and Standards| Compression Fittings | Excess Flow Valves | Instrument Manifolds,Monoflanges,Valves and Accessories | Tubing Selection

Instrument Tubing-Technical Data

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Instrument Tubing Selection

There is a huge selection of materials to choose from when selecting instrument tubing.  The selection is dependent on the service,  installation and how long the tubing is required.  It is important that these are considered before making a choice. One has to be careful when selecting polished tubing as the manufacturers polishing can work harden it and increase the surface hardness to unacceptable levels.  Thus when specifying tubing it is best to select dull annealed type,  then one can be assured that no untoward hardening has occurred.

Instrument Tubing Preparation

q       Tube Handling

The tubing surface is ESSENTIAL to sealing when using a compression fitting, hence good handling practices should be used to reduce scratches and protect surface finish.  For example dragging tubing across any surface that could scratch its surface can cause real corrosion and sealing problems.  On offshore facilities, scratches may lead to corrosion of 316SS tubing from salt water pitting.  

q       Visual Inspection of Tubing

It is a good idea to visually inspect instrument tubing to ensure it is free from scratches and other damage.  Severe scratches or damage to tubing could affect the safe installation of the compression fitting.  It is recommended that tubing in poor condition should be disposed of.  Finished tubes should be scratch free, reasonably straight and have smooth ends free of burrs.  

q       Cutting

When cutting tubing do not use a hacksaw,   the correct tool is a tube cutter which has a sharp blade.

q       Deburring

Using the correct deburring tool (usually found on the cutter),  deburr both the inside and outside edges of tube ends.  

q       Cleaning

It is recommended that instrument tubing is cleaned with dry instrument air, however where the service requires a high level of cleanliness a proprietary cleaning agent should be used.  

Instrument Tubing for Hazardous Gas Service

On hazardous gas service take care to ensure that the correct wall thickness has been chosen.  Gas molecules are small and can migrate through thinner wall tubing.  Contact your tubing supplier for details.  

Instrument Tube Bending

q       Tube Benders

On applications where bending is required, a tube bender must be used.  Follow the tube bender manufacturer’s instructions to assure good bends.  Either compression or draw type hand benders should be used for tubing up to 1/2 inches.  Above this size hydraulic tools are recommended.  

Instrument Tubing Bending & Installation - Wesley Tucker - Instruments around a plant monitor and control systems ranging from pressure differentials to contents of materials measured in percentages. Installing tubing to and from various instrument locations involves an understanding of the process and the application. Tubing installation is often dictated by the requirements of process. Bending, positioning and bracing tubing means more than just measuring a straight line and getting enough tube to fit. Tubing benders permit maximum tolerances for pressurized lines while reducing waste from cracked, misshapen or misaligned tubes of all sizes - from ehow.
Video - How to Bend 1/4 Inch Stainless Tubing - from BTC Instrumentation.
Video - Copper Tube Bending - A video of how to bend copper tube.

Minimum Straight Lengths

To ensure proper insertion depth into compression fittings minimum straight lengths of tubing are needed.  The following information may be used as a reference for the bending radius and for the minimum straight length before the bend for proper installation.

·       If the tubing O.D. is 1/2 inches or less, provide at least 25mm straight length.

·       If the tubing O.D. is greater than 1/2 inches provide at least 50mm straight length.

If the straight length is not possible, an elbow should be used.

Fitting Preparations

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.  Always ensure that the tubing material is softer than the fitting. 

Tubing Installation

q       If practical, it is recommended that instrument process impulse lines are installed in the vertical plane.  Horizontal impulse lines are generally run with a slope of not less than one in twelve between the process connection and the instrument.  Slope should be down from the tapping points for liquids and up for gases.

q       For reasons of accessibility offset and stagger tube unions wherever practicable.

q       Tube fittings must not be used to support instruments, which should be independently mounted.

q       It is recommended that any Weld splatter on stainless tubing be removed.  In severe cases, the tubing must be replaced.  

Supporting Tubing

q     It is a good idea to ensure all instrument impulse lines are as short as possible.  For lengths up to approximately 1m tubing is self-supporting, however for longer lengths it is recommended that the tubing be supported at approximately 1m intervals. 

q     The number of joints in the impulse line should be kept to a minimum.  Process and utility piping must not be used for supporting instrumentation piping or tubing.

q     Tubing should be adequately supported and braced.  It is suggested that support fixing distances not exceed the following:

Outside Diameter


1/4 inch OD

Continuously Supported

1/2 inch OD


3/4 inch OD


1 inch OD


q     It is recommended that three or more tubes run in parallel are supported in steel angle or channel, or on cable tray or ladder with appropriate insulation.

q     To avoid the possibility of corrosion, it is recommended that stainless steel tube and/or fittings (316, duplex or otherwise) is NOT be in direct contact or located directly under Zinc coated or galvanised components.

q     Electrically non-conductive tubing clamps are available. These isolate tubing from its supports,

Beware of Tubing Vibration!

It is suggested that impulse lines for instruments shall be arranged to avoid:-

·       Movement through thermal expansion.

·       Mechanical damage from impact.

When tube vibration is a problem, due to the closeness of machinery, process pressure changes or other excitation, it is recommended:

·       Tubing is clamped to the monoflange, process take-off or process line using a suitable clamp with the minimum span between the compression fitting and the clamp.

·       A vibration loop (pigtail) is installed in the tube span between the process line and any independent structure used to support the tube.  The orientation of the loop should be chosen with due regard to the probable relative motion between the connections.

·       The vibration loop crossover has a minimum clearance of 2 x tube OD to prevent fretting of the tube.

Instrument Tubing Welding

There are several instrument tube welders on the market,  they are excellent for hazardous gas applications.  These units provide consistent high quality welds when operated correctly.

Plastic Instrument Tubing

Ensure that extremely soft plastic tubing is used with an insert.  Never use metal ferrules on plastic tubing. 

Instrument Tubing Data Charts

Stainless Steel Tube - Covering Seamless Stainless Steel Tube in  Duplex, Monel, PVC sheathed copper tube and exotic metals. This technical article includes important subjects such as Ferrule hardness, 2.5% Minimum Molybdenum, Pickled & Passivated vs. Bright Annealed Tubing along with weights and working pressures 

Hoke Gyrolok® Tubing Data Charts - These charts are very useful and contain information on design, type of tubing, tubing preparation, calculating Yield, Burst, and Maximum Allowable Working Pressures, Maximum Allowable Stress Values for Material at Various Temperatures, Stainless Steel Calculation Factor Tables, Maximum Working/Burst Pressures and Tubing Tolerances. 

Pipe and Tube - Lots of very useful information here including descriptions on seamless and welded, common pipe and tube terms, manufacturing methods, nominal working pressures, pipe dimensions and weights, tube weights and working pressures. 

Useful Facts About Stainless Steel - This technical data sheet is full of useful facts and information about stainless steel.

Selection of Materials - This very useful table gives the composition of the various materials used such as 304SS and 316SS etc. 

Steel Terms and Definitions - A very useful table full of terms and descriptions.


It is strongly recommended that any personnel associated with the installation of tube fittings and tubing attend vendor courses that are Internationally available.  Tubing and fittings may look easy, however they are complex, precision items which require fully competent personnel to install them - we suggest that individuals and companies take ICEweb advice and attend a course.. Our Sponsors Prochem are Instrument Tubing and Fittings experts and have excellent Training Courses.

Instrument Tubing Links - some great information here.  

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. 

Supercritical Instrument Installations - The Tricky Process of Designing Impulse Lines for ASME B31.1 Compliance - Allan G. Gilson P.E. - When it comes to tubing, everyone knows that a grip-type tube fitting will meet or exceed the rating of the tubing itself. This makes instrument tubing installation easy—right? Simply ensure that the tubing is sized correctly, and everything will work. Piece of cake. The recent generation of coal plants in the United States (and around the world) has seen a major increase in the use of supercritical technologies due to inherent efficiency advantages over subcritical designs. However, no gain is without cost in some form. Greater efficiency requires considerably higher pressures and temperatures, resulting in significant new challenges for critical system instrument impulse line design and installation. In a supercritical plant, the pressures and temperatures for the main steam and feed water cycles routinely exceed that of conventionally fired drum-type boilers and combined cycle units. These elevated pressures and temperatures are particularly challenging for boiler manufacturers and engineers. Compliance with ASME B31.1 Power Piping requires much thicker piping and tubing walls, as well as stronger materials for valves and fittings - from FlowControl.  

Video – Techniques for Effective Tubing – Note these training videos from Yellow Jacket are for Copper Tubing only and whilst concentrating on HVAC applications have some useful tips. They cover Cutting, Deburring, Flaring, Swaging, Bending  etc. They are large downloads.

Technical Document on Instrumentation Tubing and their Connections - Nirbhay Gupta - Instrumentation tubing covers both Impulse tubes (sensing lines) as well as pneumatic tubes. Connections include tapping points, root valves and tube fittings. Usually one has to refer to a myriad of technical documents, codes and standards to search for a specific aspect of tubing design or construction. This technical note is an attempt to put all the information at one place. The efforts have been put to expose the readers to all the aspects of tubing and make them aware of all the developments in the world.

Instrument Tubing and Fittings Manual

Instrument Tubing and Fittings Manual  - This is an excellent resource from ICEweb always acknowledges Authors however it is a shame that the originator who has obviously put lots of time and effort into this blog is anonymous - anyway for whoever it was WELL DONE!

Section 1 - Instrumentation Tubing Introduction
Impulse sensing lines are the lines containing process fluid which run between the sensing instruments and process tapping points, and are usually made of tubing/piping, valves and tube fittings. This document covers Difference between a pipe and a tube, Major Advantages of Tubing over Piping Systems, Types of tubes, Guidelines for selection of instrumentation tubes, Different sizes of tubes, Criteria for selecting the size of a tube, Selection and Design criteria, Gas Service, System Pressure and Systems Temperature.

Section 2 - Design of Tubing and Tubing Systems
Covers: Class I Instrumentation Tubing Design, Requirements, Maximum Allowable Stress, Pressure and Temperature Ratings, Allowances, Dynamic Effects, Pressure Design (Internal Pressure) of Instrument Tubing/ Piping, Analysis Criterion of Tubing/Piping System, Consideration for Various Forces and Tube Bending Considerations.

Section 3 - Technical Requirements of 304 SS tubes
Suggested design requirements that should be specified when ordering 304SS tubes

Section 4 - Pneumatic Tubing
Copper tubes are primarily used for pneumatic connections. Earlier pneumatic instruments were more popular and used (controllers, transmitters, indicators etc.). Thus pneumatic tubing was used widely. However now-a-days most of the instruments that are used are electronic instruments, thus the use of pneumatic tubing is limited. Still, at present this is used to connect the pneumatic actuator and its accessories viz. positioners, I/P converters, solenoid valves etc. which are quite important from plant operation point of view. Pneumatic instruments are still prevalent in hazardous areas. Even though the pneumatic instruments are older generation, they still provide a very reliable alternative to electronic instruments. This document covers Advantages of Using Copper Tubes, Different Types of Copper Tubes, Selection of Copper Tube, Technical Requirements of Copper tube and Applicable International Standards for Copper Tubes.

Section 5 - ASTM Tubing Specifications Outside Diameter

  It is important to understand that both of the above can affect the ferrule(s) ability to seal on the tubing. It is recommended to order tubing manufactured to the plus (+) side of the outside diameter tolerance. Wall thickness variations can affect pressure ratings and flow characteristics.

Section 6 - Embedded Penetrations
Whenever the tubes have to pass through some floor slab or a wall an embedded penetration is used. This serves two purposes of (a) Supporting the tube and (b) Making a leak tight passage. 

Section 7 - Methods of Connections of Instrumentation Tubes
Covers Welded, Flared, Flareless & Compression Joints and Threaded Joints.

Section 8 - Guidelines for Take-Off Connections for Sensing Lines
Covers the Location of Pressure Taps, Considerations for Pressure Tap Design and Recommendations for Pressure Tap Design.
 Section 9 - Guidelines for Root Valves  
Isolating root valves are provided at take-off connections to isolate the entire measurement system from the main pipe line/vessel when necessary.
Section 10 - Installation of Instrumentation Tubing
Best practices for impulse tubing installation - Covers Tubing Handling, Practical Guidelines for Tube Laying and Bending, Tube Bending Check list, Characteristics of a Well-Made Tubing Circuit, Common Causes of Imperfect Bends, Routing of Bends, Guidelines for Copper Tube Installation, Guidelines for Copper tube bending and Copper tube Joints.  
Section 11 - Impulse Tube/Sensing Line Support
This section suggests principals that should be followed while designing the instrument sensing line supports.
Section 12 - Impulse Tube Installation Through EPs
In cases where tubing/piping are penetrating shielding wall, care should be taken to avoid personnel exposure to radiation streaming from radioactive sources to surrounding areas through instrument sensing lines penetrations in the shielding wall.

Section 13 - Tube Fittings  
Tube fittings are used to join or connect a tube end to another piece of equipment. This section Covers; Requirements of a Tube Fitting, Construction of a Tube Fitting, Types of Tube Fittings, Flared Fitting, Flareless Bite Type Tube Fitting, Flareless Compression Type Tube Fitting, Single Ferrule Flareless Compression Type Tube Fitting, Twin Ferrule Flareless Compression Type Tube Fitting Ferrule and its Purpose, Swaging, Operation of a Twin Ferrule Tube Fitting, Effect of Tube Thickness on Swaging, Safety Precautions for Tube Fitting Installation, Repeated Assembly and Disassembly of Tube Fitting, Specification for Stainless Steel Tube Fittings and Specification for Brass Tube Fittings.

Section 14 - Threads Used For Tube Fittings
Different types of screw threads have evolved for fastening, and hydraulic systems. Of special concern are plastic-to-metal, taper/parallel threaded joints in hydraulic circuits. A discussion and recommendations are provided to create an awareness of different types of threads and how they are used.

Section 15 - Welding Methods
This section covers; 300 Series Stainless Steels, C1018 Steel Fittings, Tig Welding, Orbital Tube Welding, Orbital Welding Equipment, Reasons For Using Orbital Welding Equipment, Industrial Applications For Orbital Welding, General Guidelines For Orbital Tube Welding, The Physics Of The GTAW Process, Material Weldability, Weld Joint Fit-Up, Shield Gas (Es), Tungsten Electrode, Welding Basics /Set-Up and Welding Parameter Development.

Section 16 - Instrument Tubing References and Suggested Reading
A list of excellent references and standards.

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

Great technical information on other products from our sponsors PROCHEM PIPELINE PRODUCTS


INSTRUMENTATION  - Includes information on; 

HYDRAULIC- Includes information on; 

VALVES AND ACTUATORS - Includes information on;

MANUFACTURING - Includes information on; 

PIPING PRODUCTS- Includes information on; 


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

Other Instrument Tubing Links

Pick the Proper Hose - Patrick Werrlein, Swagelok Company - Making a correct choice requires an understanding of hose components - The right hose keeps your process performing safely and cost effectively. The wrong hose could undermine your operations, put personnel at risk and compromise your bottom-line,  sometimes without you being aware of it - from Chemical Processing.

The following technical link is available via Swagelok
Tubing data 
An Installer’s Pocket Guide  for Swagelok® Tube Fittings – This Guide is a must for anyone associated with the Installation of Swagelok fittings. It is a large download so be prepared to wait a while.