This part of ISO 14531 specifies the physical properties and mechanical performance requirements of crosslinked polyethylene (PE-X) and polyethylene (PE) socket, saddle and spigot fittings for the connection by socket or saddle heat-fusion jointing techniques of PE-X pipes manufactured in accordance with ISO 14531-1. In addition, it lays down dimensional requirements and specifies some general material properties (including chemical stability) together with a classification scheme for PE-X fitting base materials produced in the form of pipe. This part, when used in conjunction with the other parts of ISO 14531, provides the basis for the design, manufacture and installation of PE-X piping systems (PE-X pipes, PE-X fusion fittings and mechanical fittings) for the supply of category D and category E gaseous fuels (see ISO 13623) at: a) maximum operating pressures (MOP) up to and including 16 bar1); b) a maximum operating temperature of + 60 °C; c) a minimum operating temperature of i) ? 50 °C ii) ? 35 °C iii) ? 20 °C. Conformity to this part of ISO 14531 of PE fittings for heat-fusion jointing produced in accordance with ISO 8085-3 may be claimed subject to the satisfactory conclusion of the tests listed in 5.11 and an end use restriction on operating temperature of from ? 20 °C to + 40 °C with a maximum operating pressure as determined by ISO 8085-3. NOTE Provision is made in ISO 14531-4 for the use on a restricted temperature basis of ISO 8085 fittings conforming to 5.11 in conjunction with PE-X pipe conforming to ISO 14531-1. The technical file of the fitting manufacturer should also be consulted for relevant supporting information. For installation purposes, this part of ISO 14531 provides for the jointing of heat-fusion fittings to PE-X pipes within the temperature range ? 5 °C to + 40 °C.