This document specifies requirements and test methods for fittings of prefabricated thermally insulated pipe-in-pipe assemblies, comprising a steel service fitting from DN 20 to DN 600, rigid polyurethane foam insulation and an outer casing of high density polyethylene. The quality requirements can be applied to larger dimensions. This document applies only to injected (poured) insulated fitting assemblies for continuous operation with hot water at various temperatures in accordance with clause 1 of EN 253:1993. It does not include rules for calculation of loads and stresses in the prefabricated thermally insulated pipe-in-pipe assemblies.