Stainless Steel Tubes

Test Intro

• Stainless steels have a long history of use in water applications, due to their freedom from toxicity. They can be used in plumbing, potable and waste-water projects as well as in desalination applications.

• TEST BULLET

• Stainless steel is typically and widely used in many industries where heat and chemical resistance and cleanliness are important.

• TEST BULLET 2

• Types EN 1.4301 (formerly TP304) and EN 1.4401 (formerly TP316) stainless steels are the most common stainless materials used in building services applications.

• Tubes can be jointed with threading, compression fittings, grooved, mechanical body grip ring, press-fit and welding.

• Corrosion of stainless steels can occur when the grade is not suited for the working environment or if galvanic corrosion reactions occur due to being mixed with other metals in pipework systems.

Test Outro

• ASTM A312: Standard Specification for Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes. Defines the requirements for 316L and 304L stainless steel grades. Tubes may be hot-finished welded or hot-finished seamless.  This standard defines the tubes as being suitable for elevated temperature use.

• BS EN10217-7: Welded steel tubes for pressure purposes. Technical delivery conditions. Stainless steel tubes. Defines the requirements for 1.4301, 1.4307, 1.4401 and 1.4404 stainless steel grades. Tubes are hot-finished welded. This standard defines the tubes as being suitable for low and elevated temperature use.

• BS EN10216-5: Seamless steel tubes for pressure purposes. Technical delivery conditions. Stainless steel tubes. Defines the requirements for 1.4301, 1.4307, 1.4401 and 1.4404 stainless steel grades. Tubes under this standard are hot-finished seamless. This standard defines the tubes as being suitable for low and elevated temperature use.

• BS EN10088-2: Stainless steels. Technical delivery conditions for sheet/plate and strip of corrosion resisting steels for general purposes. Defines the requirements for 1.4401, 1.4521 and 1.4301 stainless steel grades of strip and plate, but is used to confirm the material characteristics of thin-walled press-fit precision tubes and associated tube based manufactured fittings. Tubes are cold-formed welded.  This standard defines the tubes as being suitable for ambient temperature use.

• • BS3605-1 – now replaced by BS EN10216-5.
• • BS3605-2 – now replaced by BS EN10217-7.

• Thin walled (press-fit) systems are typically capable of operating up to 16 bar design pressure. However, some specifiers may restrict pressure to lower pressures, for example 6 bar for LTHW and CHW systems with press-fit jointing; 8 bar for MWCS, BCWS and DHWS systems with press-fit jointing; and 16 bar for MWCS, BCWS and DHWS systems with factory-made welded joints.

• Applications for natural gas and press-fit joints may be limited, to 54 mm and 100 mbar (as per IGEM/UP/2 Edition 2), but the current Edition 3 of IGEM/UP/2 raises this to 108 mm and 5 bar.

• For thin-walled welded stainless, above 16 bar and up to 25 bar is occasionally possible, but with bespoke selections – please consult the relevant tube manufacturer for full details.

• Thick-walled tubes (traditional) can be suitable for up to 200 bar design pressure. However it will be difficult to find fittings to suit this pressure.

  • However, some installers / end-users may restrict pressure to lower pressures, for example 25 bar. NOTE: pressure integrity is a function of jointing used, as well as application temperature and installation practices.

NOTE: Guidance only, other pressure integrities may be possible, or restrictions may be in place if products are used within particular applications where restrictions can apply (i.e. gas systems).  Consult with the relevant manufacturer or distributor to confirm actual values.

• Thin-walled press-fit: Ø12mm up to Ø108mm
• Thin-walled welded / Traditional: up to Ø1200mm

NOTE: Guidance only, other sizes may be available, or restrictions may be in place if certain coatings are to be applied.  Consult with the relevant manufacturer or distributor to confirm actual options available.

Precision / Thin-walled tubes:

• Not to be used in external area.
• Not to be used in areas where there is a high risk of mechanical damage.
• It is not advisable to use these systems in concealed areas (where joints are permanently inaccessible).

Thin-walled welded (less than SCh10S) tubes:

• Not to be used in areas where there is a high risk of mechanical damage.

Traditional / thick walled tubes:

• Suitable for most applications. 
• Suitable for both open and closed systems. 

In addition:

• There is often a need to protect stainless steel from contact with carbon steel (including ferrous swarf or debris); so separate storage and assembly areas are desirable where both carbon steel and stainless steel materials are used.
• Compatibility / dissimilar metals – care to be taken regarding galvanic corrosion risks (particularly with precision / thin-walled tubes) when stainless steel connects within a system to copper or carbon steel components.

• General considerations:
  • The appropriate PPE shall be used by operators working with stainless steel tubes.
  • Care shall be taken to ensure tubes are safety and securely stored.
  • Suitable storage bins or storage areas shall be used to ensure tubes do not roll free if not strapped or restrained.
  • Care should be taken to avoid mixing with other tubes of dissimilar metals during storage due to contamination risks.
  • Care should be taken regards any protruding tube ends to avoid contact with individuals.
  • Tubes may be in heavy loads, so care shall be taken when moving or lifting.
  • Thin-walled pipes are much lighter than their equivalent traditional pipes; hence offering significantly reduced manual handling risks.
  • When lifting by crane, or by other means, the appropriate sling configuration shall be employed, as per best practice, or as defined by a relevant Health and Safety body.
  • Any cut or machined ends shall be deburred to remove any sharp edges.
  • Appropriate measures shall be taken during cutting, threading, grooving or bending of tubes to mitigate the risk of injury to operators.
  • Appropriate measures shall be taken during any hot-working to reduce the risk of fire and to ensure adequate ventilation for operators.
• In addition for Precision / Thin-walled tubes:
  • Risk of injury by flying fragments if press adaptors and/or collars are used incorrectly, or are worn or damaged.
  • Danger of crushing by moving parts (grip jaws).

• In addition for Precision / Thin-walled tubes:
  • Risk of injury by flying fragments if press adaptors and/or collars are used incorrectly, or are worn or damaged.
  • Danger of crushing by moving parts (grip jaws).

• Please refer to the BMTFA (British Metals Tube and Fittings Association) website for additional product information and links to training material or points of contact to arrange training CPD’s. WWW.BMTFA.ORG

• The appropriate size and grade of tube shall be selected for the particular application, test and operating pressures and temperatures.
• Select the correct jointing type or fitting for the application.
• BS 5970 advises that operatives should, as far as possible, avoid touching austenitic steel surfaces with their bare hands and that surfaces should not be scratched or indented in any way because local damaged areas can form a starting point for the development of cracks in the metal, (which can lead to stress-corrosion cracking in the presence of moisture).
• There is often a need to protect stainless steel from contact with carbon steel (including ferrous swarf or debris); so separate storage and assembly areas are desirable where both carbon steel and stainless steel materials are used.
• Galvanic reactions occur if the materials are damp and in direct contact, which compromises the chromium oxide layer (that gives stainless steel its corrosion resistance).
• All tube ends must be deburred after cutting to remove sharp edges, this is especially important if the tube is being inserted into a fitting.
• Tube surfaces must be free from surface contaminants or debris that may have been picked up in storage, when transported or awaiting fabrication / installation.
• Tube bores shall be checked to ensure they are clean and free from any obstructions.
• Please check with the relevant manufacturers for any additional material preparation instructions.

• For further guidance please refer to BESA TR50 - Guide to Good Practice for Supports and Fixings.

Thin and thick – walled press-fit jointing:

• It is recommended that the press-fit jointing manufacturer is consulted to confirm the correct selection of fittings (e.g. pressure & temperature limitations, elastomer/O-ring material, etc.).
• It is advised to use a single-source supplier for all fittings within a system.
• All operatives must undergo manufacturer training.
• Powered, not manual pressing tools shall be employed to make up joints.
• Users shall ensure the calibration of pressing tools and jaws.
• It is recommended that each operative is assigned a unique ID number which they must mark on the joint so that there is traceability.
• Operators shall ensure that tubes ends are free from burrs, abrasions, indentations, projections or any other form of damage.
• Operators shall ensure that a depth gauge has been used, a “V” must be marked pointing to the end of the tube but intersecting the depth line.
• If the line is not present or not in the correct place, section should be rejected as improperly installed.
• Consideration shall be given to the support, expansion and movement provisions designed/confirmed by the press-fit joint manufacturer.
• An appropriate pressure test (note dry test for thin-walled press-fit) shall be undertaken to confirm leak tightness.

Welded jointing:

• Welder competency testing requirements is recommended.
• Operators shall ensure that all pipework or welded components are suitable in terms of material, size, pressure & temperature limitation.
• The presence of any existing protective coating shall be removed prior to welding.
• Use of dye penetrant or other forms of NDT (Non-Destructive Testing) shall be employed to validate weld quality.
• Alternatively, an appropriate pressure test shall be undertaken to confirm leak tightness.
• Consideration shall be given to the support, expansion and movement of the system

Compression or mechanical body grip ring jointing:

• The operator shall confirm that the appropriate fitting, e.g. material, size, pressure & temperature limitations, elastomer/O-ring material (if applicable), etc. are suitable for the particular application.
• Operators shall ensure that tube ends are free from burrs, abrasions, indentations, projections or any other form of damage that may impact the jointing integrity.
• Operators shall ensure that fittings are correctly applied and secured in accordance with the manufacturer's instructions or guidance notes.
• Care shall be taken to ensure that grip body fittings are positioned correctly.
• Consideration shall be given to the support, expansion and movement of the system.

Threading jointing:

• The operator shall confirm that the appropriate fitting, e.g. material, size, pressure & temperature limitations, threading compound or sealing cord material (if applicable), etc. are suitable for the particular application.
• Operators shall ensure that tube ends are free from burrs, abrasions, indentations, projections or any other form of damage that may impact the jointing integrity.
• Operators shall ensure that fittings are correctly applied and secured in accordance with the manufacturer's instructions or guidance notes.
• If threading compounds are to be used, operators shall check to ensure that the appropriate compound as a function of pressure and temperature requirements is selected, and applied as per manufacture's instructions or guidance notes.
• Care shall be taken to ensure fittings are positioned correctly to avoid cross threading.
• An appropriate pressure test shall be undertaken to confirm leak tightness.
• Consideration shall be given to the support, expansion and movement of the system.

Grooved jointing:

• The operator shall confirm that the appropriate fitting, e.g. material, size, pressure & temperature limitations, seal/gasket material etc. are suitable for the particular application.
• Operators shall ensure that tube ends are free from burrs, abrasions, indentations, projections or any other form of damage that may impact the jointing integrity.
• Operators shall ensure that rolled or cut grooved profiles satisfy the grooved coupling manufacture's fabrication and installation instructions or guidance document.
• Operators shall ensure that fittings are correctly applied, ensuring the internal seal/gasket does not become damaged.
• Coupling bodies shall be secured in accordance with the manufacturer's instructions or guidance notes.
• Consideration shall be given to the support, expansion and movement of the system.

• Expansion will be application and material specific.
• Expansion of pipework should, where possible, be accommodated naturally by incorporating expansion loops and offsets.
• Where natural expansion provisions are not feasible, proprietary expansion equipment such as bellows should be provided based on a specialist manufacturer’s design.
• Designs usually include anchor points and expansion bellows with primary and secondary guides at specific distances either side.
• The natural flexibility of the pipework layout should be assessed for its ability to accommodate thermal movement before any additional offsets or loops are added.
• Pipe supports, guides and anchors should be designed to permit / control thermal movement as required.

• Pipework insulation shall be in accordance to with BS 5970.
• Chloride concentration of insulation material must be considered appropriate for austenitic stainless steels.
• When used in conjunction with phenolic foam, it is strongly advised to adopted the recommendations of the British Stainless Steel Association and foil wrap all stainless steel pipe before insulation. BS 5970 clause 8.4.1 requires "To provide protection, aluminium foil of not less than 0.06mm thickness should be applied to the austenitic steel surface so that the insulation can be applied over the foil".
• Insulation damaged during installation shall be repaired to ensure the insulation remains effective and to reduce the risk of additional moisture ingress.
• For below-ambient temperature services, it is essential that a vapour barrier is incorporated within the insulation system.

• Water treatments will vary as a function of the application and the commissioning process employed.
• Operators shall consult with a specialist water treatment consultant or the relevant commissioning bodies for confirmation of actual requirements for water quality management.
• Operators may also wish to consult and follow the current BSRIA BG29 and BG50 guidelines.
• In low-oxygen conditions, as typically occurs under biofilms in water systems, the stable chromium dioxide layer that gives stainless steel its corrosion resistance can break down, thereby losing this protection. Sulfate reducing bacteria under the biofilm is one common cause of microbially influenced corrosion.

• Stainless steel is prone to pitting corrosion in high chloride environments. Grade 1.4404 (formerly 316L) is able to tolerate chloride content of 1000 ppm, and is a better choice than Grade 1.4307 (formerly 304L) if chlorine-based chemicals may be dosed into the system. Although 250 ppm may be a sensible upper limit for dosing, there could be a risk that overdosing occurs, particularly close to the point of chemical injection.

• The risk of galvanic corrosion as a result of the coupling of dissimilar metals should always be considered.
• Ideally, stainless steel systems of a similar grade should be used together.
• However, the presence of stainless steel may promote fast rates of corrosion within copper and/or carbon steel steels. This is a function of the volume of dissimilar materials within the system, the presence of oxygen and water treatment or other corrosion control methodologies.
• For more information: https://www.monarchmetal.com/wp-content/uploads/Galvanic-Corrosion_2.png

• There is often a need to protect stainless steel from contact with carbon steel (including ferrous swarf or debris); so separate storage and assembly areas are desirable where both carbon steel and stainless steel materials are used.
• There is a risk that large-bore thin-wall stainless steel pipework may implode under vacuum if the system is being drained and sufficient air venting points are not open to permit air entry into the section of the system being drained.
• In low-oxygen conditions, as typically occurs under biofilms in water systems, the stable chromium dioxide layer that gives stainless steel its corrosion resistance can break down, thereby losing this protection. Sulfate reducing bacteria under the biofilm is one common cause of microbially influenced corrosion.
• Stainless steel is prone to pitting corrosion in high chloride environments. Grade 1.4404 (formerly 316L) is able to tolerate chloride content of 1000 ppm, and is a better choice than Grade 1.4307 (formerly 304L) if chlorine-based chemicals may be dosed into the system. Although 250 ppm may be a sensible upper limit for dosing, there could be a risk that overdosing occurs, particularly close to the point of chemical injection.
• Jointing and pressure integrity will be a function of temperature.
• Fittings using elastomer/O-ring seals or gaskets, threading compounds or sealing cord etc. should be checked to ensure that the seal material used is appropriate for the particular application.
• Use of thin-wall press-fit stainless steel requires careful planning and quality control at all stages of the process. In particular, delivery to site, storage, avoidance of dirt ingress etc.
• Compatibility / dissimilar metals – care to be taken regarding galvanic corrosion risks when stainless steel is connected within a system to copper or carbon steel components.