Hot-dip galvanized steel pipes are first pickled on the steel parts. In order to remove iron oxide on the surface of steel parts, after pickling, they should be cleaned by ammonium chloride or zinc chloride aqueous solution or a mixed aqueous solution of ammonium chloride and zinc chloride, and then sent to a hot-dip plating tank. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion, and long service life. Hot-dip galvanized steel pipe is to make the molten metal react with the iron matrix to form an alloy layer, so that the matrix and the coating are combined. The zinc layer of hot-dip galvanized steel pipe is relatively thick, with a thickness of more than 10um. Although the surface is shiny, it is relatively rough and sequins will appear.