Welded steel pipes with hot dip coating or electric-galvanized?coating on the surface of galvanized steel pipes. Galvanizing can? increase the corrosion resistance of steel pipes and prolong their service life. Galvanized pipes are widely used, not only as pipelines for water, gas, oil and other general low-pressure fluids, but also as oil well pipes and oil pipelines in the petroleum? industry, especially in offshore oil fields, oil heaters, condensation coolers, tubes for coal distillation and washing oil?exchangers in chemical coking equipment, and tubes for trestle pipe piles and support frames in mine tunnels.