Carbon Steel Tube

• Sometimes referred to as mild steel, plain-carbon steel or low-carbon steel.​ ​
• This is one of the most commonly used type of steel, because its price is relatively low, whilst being tough and reasonably strong, and providing material properties that are acceptable for most building services applications. ​ ​
• Carbon steel contains between 0.05–0.25% carbon also making it malleable and ductile, so easy to work with. ​ ​

• Manufacturing methods, such as welded (hot-finished and cold-formed) and seamless (hot-finished), and supply condition can influence how the tube performs in service.

• Hot-finished tubes have no HAZ (Heat Affected Zone) unlike cold-formed tubes. The HAZ is an area of weakness with inconsistencies in mechanical properties. Cold-formed tubes are technically suitable for ambient temperature use only and may have some application restrictions under the PED (Pressure Equipment Directive).

• Cold-formed tubes may be suitable for other temperatures, but manufacturer's data should be consulted.  Hot-finished tubes can be certified for elevated temperature use.​ ​

• Traditional tubes have thicker walls that can be threaded, grooved or welded. They are also suitable for thick-walled press-fit jointing systems. Precision or thin-walled tubes are suitable for use within press-fit systems or compression jointing systems.​ ​

• Carbon steel is prone to corrosion, but if conditions are controlled, can have a life expectancy of many decades.​

• For water applications, traditional thick-walled tubes are suitable for systems that are either open or sealed (closed) to atmosphere. Precision or thin-walled tubes for water applications are suitable for systems sealed to atmosphere (closed) if stringent corrosion-prevention methodologies are employed, systems open to atmosphere are more at risk of corrosion and may not be suitable for use.

• BS EN10255: Non-alloy steel tubes suitable for welding and threading. Technical delivery conditions.  Replaces BS1387 which is now withdrawn.  Covers both welded hot-finished, welded cold-formed and seamless product options.  Harmonised with the CPR (Construction Products Regulations) so allows CE Marking for AVCP/CAT 3 (fuel; air and gas) and AVCP/CAT 4 (water). This will be replicated under the new UKCA marking.​

• BS EN10217-1:Welded steel tubes for pressure purposes. Technical delivery conditions. Non-alloy steel tubes with specified room temperature properties. Replaces BS3601 which is now withdrawn. When dual certified with BS EN10255 it will confirm material is cold-formed. Harmonised with the PED (Pressure Equipment Directive) – but there are some application restrictions under the PED when using cold-formed tubes. 

• BS EN10217-2:  Welded steel tubes for pressure purposes. Technical delivery conditions. Electric welded non-alloy and alloy steel tubes with specified elevated temperature properties. Replaces BS3602 which is now withdrawn. When dual certified with BS EN10255 it will confirm material is hot-finished.  Harmonised and suitable for use within PED (Pressure Equipment Directive) applications.  Elevated temperature standard, so tubes conforming demonstrate suitability for use in high temperature applications.

• BS EN10216-1:  Seamless steel tubes for pressure purposes. Technical delivery conditions. Non-alloy steel tubes with specified room temperature properties. Replaces BS3601 which is now withdrawn. Harmonised and suitable for use within PED (Pressure Equipment Directive) applications. ​

• BS EN10216-2: Seamless steel tubes for pressure purposes. Technical delivery conditions. Non-alloy and alloy steel tubes with specified elevated temperature properties.  Replaces BS3602 which is now withdrawn. Harmonised and suitable for use within PED (Pressure Equipment Directive) applications.   Seamless tubes can have very thick walls and can withstand higher design temperatures than welded tubes.​

• ISO3183 / API 5L: Specification for Line pipe:  Although this is a line pipe specification, it has a legacy of being the main standard for larger diameter pipework within building and industrial services applications.  Wall thicknesses are described in terms of Schedules. As this is an American standard, it is not harmonised with the PED.  So multi-certifying with a European standard ensures that compliance under the PED can be demonstrated.  Covers both welded hot-finished, welded cold-formed and seamless product options. ​

• BS EN10305-3:  Steel tubes for precision applications. Technical delivery conditions. Welded cold sized tubes:  Defines the technical delivery requirements for thin-walled tubes for use within press-fit systems.  Such tubes have thinner walls than traditional tubes, but due to their manufacturing and the addition of zinc coatings, these tubes have very tight tolerances and improved surface cosmetics

• BS1387 – now replaced by BS EN10255.​

• BS3601 – now replaced by either BS EN10217-1 (cold-formed welded) or BS EN10216-1 (seamless) – room temperature properties.​

• BS3602  - now replaced by either BS EN10217-2 (hot-finished welded) or BS EN10216-2 (seamless) – elevated temperature properties.

• API 5L– now available as an ISO document, ISO3183 / API 5L. 

• BS1387 – now replaced by BS EN10255.​
• BS3601 – now replaced by either BS EN10217-1 (cold-formed welded) or BS EN10216-1 (seamless) – room temperature properties.​
• BS3602  - now replaced by either BS EN10217-2 (hot-finished welded) or BS EN10216-2 (seamless) – elevated temperature properties.
• API 5L– now available as an ISO document, ISO3183 / API 5L. 

• 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.  NOTE: pressure integrity is a function of jointing used, as well as application temperature and installation practices.​

• Thick walled tubes (traditional) can be suitable for up to 200 bar design pressure.  However, some specifiers 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 typically available: Ø12mm up to Ø108mm​

• Traditional (welded and seamless typically available: Ø10.2mm up to Ø610.0mm​

• Traditional / plate based (SAW) typically available: Ø406.4mm up to Ø2540mm​

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:

  • • To be used internally only, away from areas of high humidity and away from the effects of weather.
    • 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).
    • Pipework systems also need to be closed (not open to the atmosphere) to prevent / control oxygen levels that may contribute to a higher risk of corrosion.

• Traditional / thick-walled tubes:

  • • Suitable for most applications.
    • Robust for external applications, but improved service life can be achieved if protective coatings or wraps are also used.
    • For water applications, suitable for systems that are either open or sealed (closed) to atmosphere.
    • Suitable for being buried or located within concrete slabs, again improved service life can be achieved if protective coatings or wraps are also used.

In addition:

• Compatibility / dissimilar metals – care to be taken regarding galvanic corrosion risks (particular with precision / thin-walled tubes) when carbon steel connects to copper or stainless systems.

• General considerations:

  • • The appropriate PPE shall be used by those working with carbon 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 shall be taken with regards to any protruding tube ends to avoid contact with individuals.
    • Tubes may be in heavy loads, so care shall be taken when moving or lifting.
    • 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).

• 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 CPDs @ 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.

• 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.

• Any pre-applied coating shall be removed in the localised area for hot working (i.e. welding).

• Any loose galvanised coating (as a result of cutting, bending or grooving) shall be removed via a wire brush or other suitable tool.

• 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 & Fixings @ www.thebesa.com

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 tube 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 as BESA TR/5 'Welding of carbon steel pipework' or equivalent 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:

• It shall be confirmed 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 to 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:

• It shall be confirmed 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:

• It shall be confirmed 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 manufacturer’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.
• For galvanised systems – some disbondment of the soft zinc layer on the tubes outside and inside surfaces may occur during roll grooving. This is perfectly normal, and the protective interface layer will still be intact. Any lose zinc flakes shall be removed by wire brush.  The use of a suitable touch-up rich zinc rich paint is recommended on outside surfaces only.

• 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 with BS 5970.

• Operators shall take into consideration that moisture held against mild steel/carbon steel pipework can accelerate corrosion under insulation.

• With chilled water systems using thin-wall carbon steel pipework it is advised that polyethylene coated tube insulation or a non-adhesive self-amalgamating butyl rubber, polyisobutylene or polythene tape sleeving wrap having an easily-removal disposable interleave is used. This is to mitigate against the risk of corrosion under insulation on chilled water systems.

• Insulation damaged during installation shall be repaired to ensure the insulation remains effective and to reduce the risk of additional moisture ingress.

• For pipework where a pre-applied protective coating is cut away to make joints, this area including the joints themselves, shall be tape wrapped etc. to maintain continuity of the protection and insulation.

• 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.

• Special considerations are required if using thin-walled carbon steel tubes, as aggressive cleaning chemicals may cause damage to the tubes and associated system components.

• Thin-walled carbon steels can be exposed to an enhanced risk of corrosion if not installed as per manufacturer's recommendations. Avoid drain downs and ensure oxygen is kept out of the system. Do not leave unfilled after flushing and cleaning.

• Cold-formed traditional thick-walled carbon steel tubes are more prone to corrosion than hot-finished alternatives.

• The risk of galvanic corrosion as a result of the coupling of dissimilar metals should always be considered.

• Ideally, mild steel/carbon steel/cast iron systems should be used together.

• For thin-walled carbon steel tubes, used within a fully closed system with no access to atmospheric oxygen, connections to other materials are generally unproblematic.

• However, the presence of copper and/or stainless steels may influence the galvanic corrosion reaction resulting in an increased risk of corrosion to carbon steel systems.  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

• Cold-formed thick-walled carbon steel tubes are typically imported and can suffer from internal stresses and inconsistent mechanical properties unlike hot-finished alternatives.

• Under BS EN10217-1:2019, cold-formed tubes are no longer suitable for use under the PED (Pressure Equipment Directive).

• Hot-finished thick-walled carbon steel tubes are technically superior to cold-formed tubes and provide service life improvements.

• BS EN10255 (replacement to BS1387) is technically a room temperature standard, dual certifying with BS EN10217-2 ensures a welded, hot-finished product is supplied, suitable for high and elevated temperature use.

• Under BS EN10255 a product can be CE Marked for fuel, air and gas (CAT3 applications) and water (CAT4 application) – it is imperative that if CE Marking under the CPR (Construction Products Regulations) is required that the correct CE Category is asked for and supporting documentation or tube markings confirm this.

• Jointing and pressure integrity will be a function of temperature.

• Fittings using elastomer/O-ring seals should be checked to ensure that the seal material used is appropriate for the particular application.

• Do not store or install thin-wall carbon steels on areas exposed to rainfall (i.e. roof areas, externally to buildings, or in open buildings).

• Use of thin-wall carbon steel requires careful planning and quality control at all stages of the process. In particular, delivery to site, storage, avoidance of dirt ingress, avoidance of drain downs and avoidance of air ingress following system fill by ensuring correct pressurisation and expansion settings.