ISO 18225:2012规定了基于热塑性塑料制成的用于室外供气的管道的多层管道系统的一般要求和性能要求。 它给出了由基于热塑性塑料的多层管道组成的管道系统的设计要求，其中至少60%的壁厚为聚合物材料。根据附录A，用于应力设计层和所有内层的聚合物材料必须是聚乙烯（PE）和/或交联聚乙烯（PE-X）。金属多层管的外层必须是PE或PE-X。 注:就ISO 18225:2012而言，PE-RT被视为PE，而PE-X和粘合层被视为热塑性材料。 ISO 18225:2012适用于拟在-20°C至40°C温度范围内运行的系统。它适用于这些系统中标称直径不超过630 mm的管道，以及D类（天然气）和E类（液化石油气蒸汽和天然气或液化石油气蒸汽）气体燃料的供应（见ISO 13623）。

ISO 18225:2012 specifies general and performance requirements for multilayer pipe systems based on pipes made from thermoplastics and intended to be used for gas supply outdoors. It gives requirements for the design of pipe systems consisting of multilayer pipes based on thermoplastics and for which at least 60 % of the wall thickness is of a polymeric material. The polymeric material used for stress design layers and all inner layers must be polyethylene (PE) and/or crosslinked polyethylene (PE-X), in accordance with Annex A. The outer layers of metal multilayer pipes must be of either PE or PE-X. NOTE For the purposes of ISO 18225:2012, PE-RT is considered as PE, while PE-X and adhesive layers are considered as thermoplastics materials. ISO 18225:2012 is applicable to systems intended to be operated at temperatures ranging from？20 °C to 40 °C. It is applicable to pipes in these systems having a nominal diameter up to and including 630 mm, and to the supply of gaseous fuels of categories D (natural gas) and E (LPG vapour and natural gas or LPG vapour) (see ISO 13623).