Polyurethane prefabricated buried insulation pipes are mainly used for conveying hot water in heating pipelines, usually divided into inlet insulation pipes and return insulation pipes. However, there is no strict distinction requirement for the inlet and outlet water of polyurethane prefabricated buried insulation pipes. Some thermal pipelines are distinguished by text, such as writing inlet or outlet water on the outer protective pipe of the insulation steel pipe, while others require the outer protective pipe of polyurethane prefabricated buried insulation pipes to be made in other colors