1, Hot dip galvanized pipe is to make the molten metal and iron matrix reaction and produce an alloy layer, so that the matrix and the coating are combined. Hot dip galvanizing is to first pickling the steel pipe. In order to remove the iron oxide on the surface of the steel pipe, after pickling, it is cleaned by ammonium chloride or zinc chloride aqueous solution or mixed aqueous solution of ammonium chloride and zinc chloride, and then sent into the hot dip plating tank.
Hot dip galvanizing has the advantages of uniform coating, strong adhesion and long service life. Matrix of hot dip galvanized steel pipe. Complex physical and chemical reactions occur between galvanized pipe and molten bath to form a compact zinc-iron alloy layer with corrosion resistance. The alloy layer is integrated with the pure zinc layer and the steel tube matrix, so its corrosion resistance is strong.
2, Cold galvanized pipe is electric galvanized, galvanized amount is very small, only 10-50g/m2, its own corrosion resistance is much different than hot galvanized pipe. The galvanized layer of cold galvanized steel pipe is the electroplating layer, and the zinc layer is independently layered with the steel pipe matrix.
Zinc layer is thin, zinc layer is simply attached to the steel tube matrix, easy to fall off. So its corrosion resistance is poor. It is prohibited to use cold galvanized steel pipes as water supply pipes in newly built houses.