Polyurethane insulated pipes are made by foaming high-performance polyether polyol composite materials and multiple methyl polyphenyl polyisocyanates through chemical reactions. Polyurethane foam insulation pipes have excellent characteristics such as light bulk density, high strength, insulation, sound insulation, flame retardancy, cold resistance, corrosion resistance, non water absorption, and easy and fast construction. They have become indispensable products for insulation, waterproofing, sealing, and other industrial sectors such as petroleum, chemical, power, construction, transportation, and refrigeration. 
First layer: Working steel pipe layer 
According to the design and customer requirements, seamless pipes (GB8163-87), spiral welded pipes (GB9711-88; SY/T5038-92), and straight seam welded pipes (GB3092-93) are generally selected. After advanced shot blasting and rust removal process, the rust removal grade of the steel pipe can reach Sa2 level in GB8923-1988 standard, and the surface roughness can reach R=12.5 microns in GB6060.5-88 standard. 
Second layer: Polyurethane insulation layer 
It is made by injecting the original liquid of rigid polyurethane foam into the cavity formed between the steel pipe and the outer protective layer with a high-pressure foaming machine. It is commonly known as the "pipe in pipe foaming process". Its functions include waterproofing, insulation, and supporting the self weight of the heating network. When the temperature of the conveying medium is -50 ℃ -120 ℃, rigid polyurethane foam is selected as the insulation layer. 
The third layer: The high-density polyethylene protective layer is prefabricated into black (yellow) plastic pipes with a certain wall thickness, which serves to protect the polyurethane insulation layer from mechanical damage and prevent corrosion and waterproofing. 
Suitable for insulation and cooling engineering of various media transported within the range of -50 ℃ to 150 ℃. It is widely used in insulation and cooling projects for urban centralized heating, warm rooms, cold storage, coal mines, oil ports, chemical industries, and other industries. 
1. Reduce project costs. 
According to relevant departments' calculations, double pipe heating pipelines can generally reduce project costs by about 25% (using fiberglass as a protective layer) and 10% (using high-density polyethylene as a protective layer). 
Low heat loss and energy conservation. 
Its thermal conductivity is: λ=0．013—0．03kcal/m·h·oC， It is much lower than other commonly used pipeline insulation materials in the past, and the insulation effect is improved by 4-9 times. Moreover, its water absorption rate is very low, about 0.2kg/m2. The reason for low water absorption is that the closed cell rate of polyurethane foam is up to 92%. Low thermal conductivity and low water absorption, combined with insulation layer and high-density polyethylene or fiberglass protective shell with good waterproof performance, have changed the traditional situation of "wet cotton jacket" for laying heating pipelines in underground trenches, greatly reducing the overall heat loss of heating pipelines. The heat loss of the heating network is 2%, which is less than the international standard requirement of 10%. 
3. Anti corrosion, good insulation performance, and long service life. 
As the polyurethane rigid foam insulation layer is closely bonded to the outer skin of the steel pipe, it can isolate the infiltration of air and water and play a good anti-corrosion role. At the same time, its foam pores are all closed, and its water absorption is very low. The high-density polyethylene shell and fiberglass shell both have good anti-corrosion, insulation, and mechanical properties. Therefore, the outer skin of the working steel pipe is difficult to be eroded by external air and water. As long as the water quality inside the pipeline is well treated, its service life can reach more than 50 years, which is 3-4 times longer than traditional trench laying and overhead laying. 
4. Pipeline insulation. Less land occupation, faster construction, and favorable environmental protection. 
Directly buried heating pipeline insulation does not require the construction of large trenches, only the insulation pipes need to be buried underground, thus greatly reducing the project land occupation, reducing excavation volume by more than 50%, and reducing civil engineering masonry and concrete volume by 90%. At the same time, the processing of insulation pipes and on-site trenching are carried out in parallel, and only on-site joints are required, which can shorten the construction period by more than 50%.