Hot dip galvanized pipe It is to make the molten metal react with the iron matrix to produce an alloy layer, so as to combine the matrix and the coating. Hot dip galvanizing is to pickle the steel pipe first. In order to remove iron oxide on the surface of the steel pipe, after pickling, it is cleaned in ammonium chloride or zinc chloride aqueous solution or ammonium chloride and zinc chloride mixed aqueous solution tank, and then sent to the hot dip galvanizing tank. Hot dip galvanizing has the advantages of uniform coating, strong adhesion and long service life. Most of the processes in the North adopt the process of directly rolling pipe with galvanized strip for zinc supplement.