Construction polyethylene pipe insulation and some forms of hydrophobic closed system uses flexible layout, reasonable structure, safe and reliable. Row tide steel casing pipe on both timely discharge moist gas, but also as a daily alarm signal tube running. Thermal compensation pipeline of high quality bellows compensation temperature steam pipe insulation, and installed in the casing, made of buried form, without the provision of observation wells heat pipe insulation, construction convenient operation, short construction period. For conveying 2.5MPa, 350 degrees Celsius below the steam or other media, the product made with steel outer protective layer, high strength, not damaged, the construction is simple maintenance, long service life superior rigid polyurethane foam insulation and external insulation with High-density polyethylene outer sheath (jacket layer) forming a production process, we call this "one-step", Mr. outputs high density polyethylene outer sheath, then the gap between the outer protective layer of polyethylene and steel pipes then casting the production process of polyurethane rigid foam insulation is that we often say "two-step"