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.

　　使用了聚氨酯直埋保温管导热系数低、隔热性能好的硬质聚氨酯作为隔热材料，具有优异的隔热性。预制直埋保温管现场接头保温须在试压合格后方可进行，现场接头保温施工。这一项内容是预制直埋保温管道施工特有的施工质量好坏直接影响使用寿命。保温层有现场发泡施工和保温瓦施工两种方法，不论采用哪种方法施工，都不能出现环形空间，开裂、脱层等缺陷，维护层的做法有多种（如高密度聚乙烯和玻璃钢保护层）但都能保证接头的整体性，严密性，防水性。

　　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.

　　聚氨酯直埋保温管由于聚氨酯硬质泡沫保温层紧密地粘结在钢管外皮，隔绝了空气和水的渗入，能起到良好的防腐作用。同时它的发泡孔都是闭合的，吸水性很小。高密度聚乙烯外壳、玻璃钢外壳均具有良好的防腐、绝缘和机械性能。因此，工作钢管外皮很难受到外界空气和水的侵蚀。吸水率低的原因是由于聚氨酯泡沫的闭孔率高达92%左右。

　　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%.

　　低导热系数和低吸水率，加上保温层和外面防水性能好的高密度聚乙烯或玻璃钢保护壳，改变了传统地沟敷设供热管道“穿湿棉袄”的状况，大大减少了供热管道的整体热损耗。

　　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.