According to the design and requirements of customers generally use seamless (GB8163-87) spiral welded pipe (GB9711-88; SY / T5038-92) and welded pipe (GB3092-93). Advanced steel surface after shot blasting process, steel rust rating up to GB8923-1988 standard Sa2 grade, surface roughness up GB6060.5-88 standard R = 12.5 microns. Second layer: polyurethane insulation in the cavity with a high pressure foaming machine steel tube between the outer protective layer is formed in a one-time injection of a rigid polyurethane foam stock solution is made. Commonly known as "pipe-in-pipe foaming process." First, its role waterproof, two insulation, three heating network is to support the weight. When the transmission medium temperature: -50 ℃ -120 ℃, the selection of rigid poly semicarbazide acetate foam insulation do. Third layer: high-density polyethylene pipe insulation protection layer of polyurethane, high density polyethylene pipe insulation polyurethane foam, polyurethane foam pipe insulation, by the conveying medium, the work steel, foam insulation layer, an outer protective polyethylene plastic pipe, through combination of equipment turn out. Polyurethane insulation