Polyurethane insulated steel pipe has a wide range of applications in indoor and outdoor pipelines, including central heating, central air conditioning, chemical industry, medicine and so on. There are many preparations to be done before the construction of polyurethane direct buried insulation pipe. We should follow the correct steps. If there are some problems in the process of using polyurethane directly buried insulation pipe, it is likely that our use method is wrong, so we should strictly abide by the operation procedures before construction, without any mistakes.
The rigid polyurethane with low thermal conductivity and good thermal insulation performance is used as thermal insulation material, which has excellent thermal insulation. The on-site joint insulation of prefabricated directly buried insulation pipe can only be carried out after the pressure test is qualified. This content is that the special construction quality of prefabricated directly buried insulation pipeline directly affects the service life. There are two methods for the construction of thermal insulation layer: field foaming construction and thermal insulation tile construction. No matter which method is adopted, there shall be no defects such as annular space, cracking and delamination. There are many methods for the maintenance layer （such as high-density polyethylene and glass fiber reinforced plastic protective layer）， but they can ensure the integrity, tightness and water resistance of the joint.
The polyurethane directly buried thermal insulation pipe is tightly adhered to the outer skin of the steel pipe because of the rigid polyurethane foam insulation layer, which can isolate the infiltration of air and water, and can play a good anti-corrosive effect. At the same time, its foam pores are closed and its water absorption is very small. HDPE shell and FRP shell have good anticorrosion, insulation and mechanical properties. Therefore, the outer skin of the working steel pipe is hard to be eroded by the outside air and water. The reason for low water absorption is that the polyurethane foam has a closed porosity of about 92%.
Low thermal conductivity and low water absorption, combined with thermal insulation layer and high-density polyethylene or glass fiber reinforced plastic protective shell with good waterproof performance, change the situation of "wet cotton padded jacket" of traditional trench laying heating pipeline, greatly reduce the overall heat loss of heating pipeline.
