1. Stress resistance and aging resistance. Using high-quality improved PVC project plastic extrudes once, with high strength of shaping molding; the inner grid shape forms physics Steel structure, its rigidity is 10-100 times higher than common plastic pipe. It is not necessary to envelop, can replace steel tube put through the road safely. Smolder (namely the ability of quenching is good), anti corrosion, aging resistance, with the longevity of over 50 years.