The difference between hot-dip galvanized steel pipe and cold-dip galvanized steel pipe

Hot-dip galvanizing pipe reacts molten metal with an iron matrix to produce an alloy layer, thereby combining the matrix and the coating. Hot-dip galvanizing is to pickle the steel pipe first. To remove the iron oxide on the surface of the steel pipe, after pickling, it is cleaned in an aqueous solution of ammonium chloride or zinc chloride 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. The hot-dip galvanized steel pipe matrix undergoes complex physical and chemical reactions with the molten plating bath to form a corrosion-resistant zinc-iron alloy layer with a tight structure. The alloy layer is integrated with the pure zinc layer and the steel pipe matrix, so it has strong corrosion resistance.

Cold-dip galvanized pipe is electro-galvanized. The amount of galvanizing is very small, only 10-50g/m2. Its corrosion resistance is much worse than that of hot-dip galvanized pipe. Regular galvanized pipe manufacturers, to ensure quality, do not use electro-galvanizing (cold plating). Only small businesses with small-scale and old equipment use electro-galvanizing, and of course, their prices are relatively cheaper. The Ministry of Construction has officially announced that cold-galvanized pipes with backward technology will be phased out and cold-galvanized pipes are not allowed to be used as water and gas pipes. The zinc layer of cold-dip galvanized steel pipe is electroplated, and the zinc layer is layered independently from the steel pipe matrix. The zinc layer is thin, and the zinc layer simply adheres to the steel pipe matrix and falls off easily. Therefore, its corrosion resistance is poor.

Post time: Nov-21-2023

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