Galvanized steel pipe is divided into two types: hot- dip galvanized steel pipe and cold- galvanized steel pipe
Hot- dip galvanized steel pipe : Hot- dip galvanized pipe is to make the molten metal react with the iron matrix to produce an alloy layer, so that the matrix and the coating are combined. Hot-dip galvanizing is to first pickle the steel pipe. In order to remove the iron oxide on the surface of the steel pipe, after pickling, it is cleaned in a tank with ammonium chloride or zinc chloride aqueous solution or a mixed aqueous solution of ammonium chloride and zinc chloride, and then sent to Hot dip plating tank. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion and long service life. Hot dip galvanized steel substrate with the molten bath complicated physical, chemical reaction galvanized steel should be, to form a tight corrosion resistant zinc-iron alloy layer structure. The alloy layer is integrated with the pure zinc layer and the steel pipe matrix. Therefore, its corrosion resistance is strong.
Cold galvanized steel pipe : Cold galvanized pipe is electro-galvanized, and the amount of galvanization is very small, only 10-50g/m2, and its corrosion resistance is much worse than that of hot- dip galvanized pipe . Most of the regular galvanized pipe manufacturers do not use electro-galvanized (cold plating) in order to ensure quality. Only those small enterprises with small scale and outdated equipment use electro-galvanization, and of course their prices are relatively cheaper. Currently the Ministry of Construction has formally below, eliminate backward technology of cold galvanized pipe , in the future are not allowed to cold galvanized pipe for water and gas pipes. The galvanized layer of cold galvanized steel pipe is an electroplated layer, and the zinc layer is separated from the steel pipe matrix. The zinc layer is thin, and the zinc layer simply adheres to the steel pipe substrate and is easy to fall off. Therefore, its corrosion resistance is poor. In newly-built houses, it is prohibited to use cold- galvanized steel pipes as water supply pipes.