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Technical Bulletin 120: The use of pliable corrugated (stainless steel) tubing in domestic and non-domestic gas installations

Date issued: 11 August 2021

This article was published in the October 2021 edition of Registered Gas Engineer

This Technical Bulletin provides guidance to Gas Safe registered businesses/engineers on the use of pliable corrugated (stainless steel) tubing and fittings for domestic and non-domestic installations.

Industry standards (product)

Pliable corrugated (stainless steel)tubing (PCSST) is manufactured to the requirements of BS EN 15266(1).

PCSST meeting this manufacturing standard is a high-quality product that can be used as an alternative to more traditional, rigid steel and copper pipework for fuel gases.

Industry standards (installation requirements)

The industry standards covering the installation of PCSST are:

  • BS 6891(2)
  • IGEM/UP/2(3)
  • PD 54823:2016(4)

Clarification on some of the questions relating to the use of PCSST within these standards is provided below.

Pipes passing through walls and floors

Although PCSST has a factory-applied cover(s), when passing through walls or floors it is treated the same as other gas pipework material and should be located in a separate sleeve passing through the full width of the wall or the full thickness of the floor. This applies to installation pipework for all gas types, ie, natural gas (NG), liquefied petroleum gas (LPG) and LPG/air.

Note 1: Sleeves for gas pipework need to be manufactured from a corrosion resistant material that is impermeable to gas and is capable of protecting the pipework against failure caused by movement of the structure, eg, continuous lengths (no joints) of copper, steel, polyethylene, and be installed in accordance with relevant industry standards.

PCSST mechanical fittings

PCSST tubing and fittings need to be assembled in accordance with the manufacturer’s instructions. Only fittings and tubing from the same manufacturer should be used. It is not permitted to use the fittings from one manufacturer with the tubing of a different manufacturer. BS 6891 states in Clause 7.3: “Any mechanical joint shall be located in a readily accessible position that allows the fitting to be tightened to make a gas-tight joint.”

IGEM/UP/2 states in Clause 6.7.2: “Joints shall be located in readily accessible positions for inspection and maintenance.”

Fittings manufactured and compliant with BS EN 15266 are defined as mechanical fittings and should not be concealed within the fabric of the building, placed within a sleeve or buried either internally or externally. Fittings of this type need to be installed in a readily accessible and ventilated space and must not be located within a fire-protected area such as protected shafts, lobbies and corridors.

The installation of PCSST in unventilated ducts or voids Regulation 19(6) of GSIUR states: “Where any installation pipework is not itself contained in a ventilated duct, no person shall install any installation pipework in any shaft, duct or void which is not adequately ventilated.”

Note 2: Similar legislative requirements apply in other geographical areas covered by Gas Safe Register. For details of current gas safety legislation, building legislation and industry standards for the geographical areas covered by Gas Safe Register, see the Legislative, Normative & Informative Document List (LNIDL).

Clause 8.16.1 of BS 6891 states:

  • “Vertical and horizontal ducts containing pipework shall be ventilated to ensure that minor gas leakage does not cause the atmosphere within the duct to become unsafe.
  • Any ventilation opening shall be located such that air movement can occur within the duct.
  • Any ventilation opening shall lead to a safe place, preferably to outside air.
  • Ducts shall be sealed from any cavity, wall or floor void through which they pass.”

IGEM/UP/2, which covers both NG and LPG in a non-domestic environment, states in Clause 10.6: “Pipework must not be installed in an unventilated duct, void or enclosure. Where it is necessary to pass pipework through an unventilated void, the following options are available:

  • The pipework shall be sleeved continuously through the unventilated duct or void, with the sleeve ventilated at one or both ends into a safe area, or
  • The unventilated duct or void shall be filled with a material infill to reduce to a minimum the volume of any gas that can accumulate. The infill material should be of a dry, chemically neutral and fire-resistant nature, for example, crushed slate chippings or dry, washed sand.”

IGEM/UP/2 also clarifies in Clause, in relation to PCSST, that: “Where pipework is required to be enclosed in a sleeve, for example, when passing through a wall or an unventilated void, the factory applied coating on copper pipe or pliable corrugated stainless steel tube shall not be considered to fulfil such a purpose.”

Note 3: Manufacturers of PCSST in the UK may offer innovative dual-covered products designed to be used within unventilated ducts or voids. Products of this type are not currently covered by any normative manufacturing standard. Before using products of this type, users should ensure the product has been independently assessed by a third-party test authority against pre-determined test criteria to ensure it is fit for purpose. See also Status of Manufacturer’s Technical Specification/Guidance.

Installation of PCSST within a fire-protected area

For the purpose of this TB, the term protected area is used in relation to fire safety and is a ventilated space containing gas pipework and isolated from other parts of the building within fire-resisting construction. Examples of protected areas will include a protected stairway, a protected corridor/lobby and a protected entrance hall/landing.

Note 4: Reference should be made to Annex D of BS 6891 for additional guidance on fire protected areas

For the installation of PCSST within a protected area, BS 6891 Clause 8.19 states: “In addition to the requirements for fire resistance fire stopping, any pipework carrying gas installed in, or passing through, a protected area shall be:

  • Steel pipework with screwed joints
  • Steel pipework with welded joints
  • Continuous length of copper (no joints), or
  • Continuous length of pliable corrugated (stainless-steel) tubing manufactured to withstand Fire Test A of BS EN 1775:2007(5), Annex A.

Note 5: PCSST manufactured to BS 7838 [Standard now withdrawn] meets Fire Test A. For pliable corrugated tubing manufactured to BS EN 15266, the manufacturer should be consulted.

In the non-domestic environment, the guidance published in IGEM/UP/2 Clause 7.2.5 states: “Pipework must not pass through or along a protected shaft containing a stair or lift (see The Building Regulations), unless all the following conditions apply:

  • OP (Operating pressure) does not exceed 75mbar, and
  • Pipework, including fittings, is of carbon or stainless steel
  • Any joint is either threaded (screwed) or welded
  • Pliable corrugated stainless steel tube is of continuous length without joints manufactured to withstand fire test A of BS EN 1775, Annex A.

Pliable corrugated (stainless steel) tubing manufactured to BS EN 15266 may be tested to meet Fire Test A, Fire Test B or both. The PCSST manufacturer should be consulted to confirm which fire test has been achieved before installing the pipe within any fire-protected areas.

Direct burial of PCSST (internally and externally)

BS 6891 states that where PCSST is to be directly buried:

  • It shall conform to BS 7838 [Standard now withdrawn] or BS EN 15266
  • The manufacturer’s instructions allow for direct burial
  • It is installed in accordance with the manufacturer’s instructions, and
  • It has a factory-applied cover with a minimum thickness of 0.5mm, manufactured from a non-chlorinated material of a synthetic polymer or elastomer with a total chloride content not exceeding 50ppm.

Products manufactured to BS EN 15266 may not meet the above requirements for minimum thickness of cover and maximum chloride content as the requirements were originally part of the now withdrawn BS 7838 and do not form part of BS EN 15266. The PCSST manufacturer should be consulted before the product can be directly buried internally or externally.

With regard to burial of PCSST in non-domestic situations, IGEM/UP/2 states in the notes to Clause that products only complying with BS EN 15266 cannot be directly buried in the ground or screed unless additional corrosion protection is applied.

It also states that BS 7838 [Standard now withdrawn] products are suitable for direct burial without the need for additional protection.

Because BS 7838 has been withdrawn, before using a product manufactured to BS EN 15266 for direct burial internally or externally, the PCSST manufacturer should be consulted to confirm that this is acceptable practice for its particular product.

For both BS 6891 and IGEM/UP/2, suitable methods of burying PCSST and the required burial depths are stipulated depending on the situation and these would need to be applied as appropriate. The PCSST manufacturer should also be contacted for any specific requirements for their individual product.

Status of manufacturer’s technical specification/guidance

Installation guidance published by product manufacturers may be deemed as appropriate standards within the meaning of the Gas Safety (Installation & Use) Regulations 1998, provided that the technical specification/guidance provides, in use, equivalent levels of safety, suitability and fitness for purpose to those achieved by the relevant standard(s) to which it is expressed to be equivalent.

Registered businesses/engineers are responsible for ensuring that the methods adopted for PCSST product installation satisfy the requirements of all relevant regulations.

Note 6: For general information about the process behind the development of Gas Safe Register Technical Bulletins and the expectations for all Stakeholders, see TB 1000 by logging into your online account at:

(1) BS EN 15266: 2007 – Incorporating corrigendum April 2008 – Stainless steel pliable corrugated tubing kits in buildings for gas with an
operating pressure up to 0.5 bar
(2) BS 6891:2015 + A1 2019 Specification for the installation and maintenance of low pressure gas installation pipework of up 35mm (R1 1/4) on premises
(3) IGEM/UP/2 Edition 3 – Installation pipework on industrial and commercial premises (Communication 1771)
(4) PD 54823: 2016 – Guidance for the design, commissioning and maintenance of LPG systems in small craft
(5) BS EN 1775: 2007 Gas supply. Gas supply for buildings. Maximum operating pressure less than or equal to 5 bar.

Note 7: Gas Safe Register Technical Bulletins and the Legislative, Normative & Informative Document List can be viewed by logging into your
online account at: