Direct-buried prefabricated thermal insulation pipe is made by closely attach- ing the transm- ission medium of steel pipe ,polyurethane hard foamed thermal insulation layer and HDPE outer casing This project is mainly used on urban central heating networks, petroleum transmission pipelines , water supply pipe- lines in high and cold areas and industrial pipeline projects in factory areas . It has the advantages of highly effective thermal insulation,water resistance and corrosion resis－ tance and resistance to puncture by plant roots. Trench laying is not required during construct－ ion and it can be directly buried in the frozen earth layer 0.6to 1.2m deep。The amount of thermal loss can be reduced by 40%as compared with the traditional process. Its service life can reach 30 to 50 years, which is 3to 5 times longer than other thermal insulat-ion and corrosion resistant materials.
