This European Standard specifies requirements and test methods for straight lengths of prefabricated thermally insulated pipe-in-pipe assemblies for directly buried hot water networks, comprising a steel service pipe from DN 20 to DN 1200, rigid polyurethane foam insulation and an outer casing of polyethylene. This standard applies only to insulated pipe assemblies, for continuous operation with hot water at various temperatures up to 120 °C and occasionally with a peak temperature up to 140 °C. The estimation of expected thermal life with continuous operation at various temperatures is outlined in annex B.