The hot-dip galvanizing tube is to make the molten metal react with the iron matrix to produce the alloy layer, so that the matrix and the two layers of the coating are combined. Hot dip galvanizing is to pickle steel pipes first, then remove iron oxides on the surface of steel pipes, then pickle them, then clean them through ammonium chloride or zinc chloride water solution or ammonium chloride and zinc chloride mixed water solution tank, then send them into hot dip bath.
Hot dip galvanizing has the advantages of uniform coating, strong adhesion, long service life and so on. The complex physical and chemical reactions occurred between the steel tube matrix and the molten plating bath to form a corrosion-resistant and tightly structured zinc - iron alloy layer. The alloy layer is integrated with the pure zinc layer and the steel tube matrix, so its corrosion resistance is strong.
Cold galvanizing is electrogalvanizing, with little galvanizing, and its corrosion resistance is much different from that of hot galvanized pipe. Regular galvanized pipe manufacturers, in order to ensure quality, most of them do not use zinc plating. Only those small and old equipment, old and small businesses use zinc plating, of course, their prices are relatively cheaper.
At present, cold galvanized pipes are not allowed to be used as water and gas pipes. The zinc layer is electroplating layer, and the zinc layer and the steel tube matrix are stratified independently. The zinc layer is thinner and the zinc layer is simply attached to the steel tube matrix, which is easy to fall off. Therefore, its corrosion resistance is poor. In newly built houses, cold galvanized steel pipes are forbidden to be used as water pipes.
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