This European Standard provides requirements and test methods for flexible, pre-insulated, directly buried district heating pipe assemblies with metallic service pipes and bonding between the layers of the pipes and thermal insulation materials of polyurethane or polyisocyanurate foam, the casing pipes being made of polyethylene. This European Standard is valid for maximum operating temperatures up to 140 °C and pressures up to 25 bar for a design lifetime of at least 30 years. NOTE For higher temperatures or for the transport of other fluids, for example potable water, additional requirements and testing is needed. Such requirements are not specified in this European Standard.