By the transmission medium, the work of steel, foam insulation, polyethylene plastic outer sheath tube, followed by the combination of the device outside of the first layer: Working pipe layer depending on the design and requirements of customers generally use seamless (GB8163-87) Spiral welded pipe (GB9711-88; SY / T5038-92) and Longitudinal (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 protective layer of a certain thickness of precast black (yellow) plastic pipe, its role from one protective polyurethane insulation mechanical hard object damage, and second, anticorrosion and waterproof. Specifications: OD mm 238 mm 3.5 Weight Kg 2.475 wall thickness tolerances mm ± 0.28 mm 159 corresponding pipe diameter corresponding insulation thickness corresponding sleeves mm 245 mm 37 Features: 1, lower project cost. 2, low heat loss and save energy. 3, good corrosion, insulation performance, long service life. 4, small footprint, fast construction, favorable environmental protection.