Galvanized steel pipes are divided into cold galvanized steel pipes and hot galvanized steel pipes.

Cold galvanized steel pipes have been banned, the latter is also advocated by the state can be used temporarily. In the sixties and seventies, developed countries began to develop new types of pipes, and one by one, galvanized pipes were banned. The Ministry of Construction of China and four other ministries and commissions have also issued a document clearly prohibiting the use of galvanized pipes as water supply pipes from 2000 onwards. Hot-dip galvanized steel pipes are widely used in fire fighting, electricity and highways.

Hot-dip galvanized pipe

Hot-dip galvanized pipe is made by reacting molten metal with iron substrate to produce an alloy layer, thus combining both the substrate and the coating. Hot-dip galvanizing is done by pickling the steel pipe first, in order to remove the iron oxide on the surface of the pipe, pickling it and then cleaning it by ammonium chloride or zinc chloride in aqueous solution or mixed ammonium chloride and zinc chloride in aqueous solution bath, and then feeding it into a hot dip galvanizing bath. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion and long service life. The hot-dip galvanized steel pipe substrate reacts with the molten plating solution in a complex physical and chemical reaction to form a corrosion-resistant, structurally compact zinc-iron alloy layer. The alloy layer is integrated with the pure zinc layer and the steel pipe substrate, so its corrosion resistance is strong.

Cold Galvanized Pipe

Cold galvanized pipe is galvanized, the amount of galvanization is very little, only 10-50g/m2, and its own corrosion resistance is much worse than that of hot dip galvanized pipe. Most of the regular galvanized pipe manufacturers do not use electro galvanizing (cold galvanizing) in order to ensure quality. Only those small enterprises with small scale and obsolete equipment use electro galvanizing, and of course their prices are relatively cheaper. The Ministry of Construction has formally issued the following order to eliminate the backward technology of cold galvanized pipes and forbid the use of cold galvanized pipes for water and gas pipes. Cold galvanized steel pipe galvanized layer is electroplated layer, the zinc layer and the steel pipe substrate independent of each other. The zinc layer is thin, and the zinc layer is simply attached to the steel pipe matrix and easily peels off. Therefore, its corrosion resistance is poor. In new residential buildings, it is prohibited to use cold galvanized steel pipes as water supply pipes.

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