ISO 18225:2012

Overview - ISO 18225:2012 (Multilayer piping systems for outdoor gas installations)

ISO 18225:2012 specifies general and performance requirements for multilayer thermoplastic piping systems intended for outdoor gas supply. It covers pipe system design where at least 60% of the wall thickness is polymeric and where the stress-bearing and inner layers are made of polyethylene (PE) and/or crosslinked polyethylene (PE‑X) (Annex A). The standard applies to systems operating between −20 °C and 40 °C, for nominal diameters up to and including 630 mm, and for gaseous fuel categories D (natural gas) and E (LPG vapour / natural gas or LPG vapour).

Keywords: ISO 18225:2012, multilayer piping systems, outdoor gas installations, PE, PE‑X, PE‑RT, gas supply pipes.

Key technical topics and requirements

• Material requirements
  • Stress-designed and inner layers must be PE or PE‑X; PE‑RT is treated as PE for the standard.
  • Outer layers of metal multilayer (M‑pipes) must be PE or PE‑X.
  • At least 60% of total wall thickness must be polymeric.
• Design and dimensional rules
  • Applicable to pipes up to DN/OD 630 mm.
  • Defines geometrical terms (nominal diameter, mean/inside/outside diameter, layer thickness).
• Performance and service conditions
  • Systems designed for operation from −20 °C to 40 °C.
  • Applies to gaseous fuels categories D and E (see ISO 13623).
  • Includes requirements for design pressure, long-term strength (MRS/LPL concepts), and ring stiffness.
• Testing and verification
  • References and includes test methods for adhesion of layers, long-term strength, resistance to gas constituents, and weathering of outer layers (Annexes B and C).
  • Normative references list product and test standards used to demonstrate fitness for purpose.
• Fittings, seals and documentation
  • Requirements cover compatible fittings, elastomeric seals, marking, and documentation for traceability and installation.

Practical applications and who uses this standard

• Utility companies and gas network operators specifying materials for outdoor gas distribution.
• Pipe and fittings manufacturers designing multilayer PE/PE‑X piping systems (including PE/metal/PE constructions).
• Engineers and designers conducting system design, pressure and long‑term strength calculations.
• Test laboratories and certifiers verifying compliance with multilayer pipe performance, adhesion and weathering tests.
• Specifiers and procurement teams writing technical specifications for pipelines supplying natural gas or LPG vapour.

Related standards

ISO 18225 references and complements other ISO standards for thermoplastic pipes and testing (examples include ISO 161-1, ISO 3126, ISO 17456, ISO 9080 and ISO 14531 series) and aligns with fuel-category guidance in ISO 13623.

Using ISO 18225:2012 helps ensure safe, durable and compliant multilayer piping systems for outdoor gas installations by specifying clear material, design and test requirements.