District heating pipe - insulated by polyurethane foam in outer PVC tube with mineral wool interlayer

摘要

Steel pipes for use in district heating systems for burial underground are enclosed in outer tubes, made of PVC, and insulated by polyurethane foam. The space between each pipe and the foam layer is filled out by semicylindrical shells of mineral wool. At the ends of each pipe the foam layer extends radially inward to the steel pipe. In sections which include an expansion bend, the mineral wool shells are replaced by polystyrene shells. This prevents cracks in polyurethane (which must not be heated above 130 deg.C) by the heating medium which has a temp. in excess of 140 deg.C.