Surface is hot-dip plated or galvanized layer welded steel pipe. Hot-dip galvanizing can increase the corrosion resistance of steel pipes and prolong the service life. Galvanized square tube is widely used, in addition to water, gas, oil and other general low-pressure fluid pipeline, but also for the oil industry, especially offshore oil wells, pipeline, pipe with the tube, as well as the bridge bridge pile, mine tunnel support frame with the tube. The galvanized square tube is an alloy layer produced by the reaction of the molten metal with the iron matrix, so that both the substrate and the plating layer are combined. Hot-dip galvanizing is the first pickling of the steel pipe, in order to remove the iron oxide surface of the steel pipe, pickled, through ammonium chloride or zinc chloride water solution or ammonium chloride and zinc chloride mixed aqueous solution And then into the hot-dip plating tank. Often used galvanized pipe, galvanized pipe i…