The hot-dip
galvanized steel tube is obtained by reacting a molten metal with an iron matrix to produce an alloy layer, thereby combining the substrate and the plating layer. Hot-dip galvanizing is the first step of pickling the steel pipe in order to remove the iron oxide on the surface of the steel pipe. After pickling, it is washed by 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 bath. Hot-dip galvanizing has the advantages of uniform plating, strong adhesion and long service life. The hot-dip galvanized steel pipe base and the molten plating solution are complex physical and chemical anti-galvanized steel pipes, and a corrosion-resistant structure of zinc-iron alloy layer is formed. The alloy layer is integrated with the pure zinc layer and the steel pipe base. Therefore, its corrosion resistance is strong.
The cold-galvanized steel pipe is electro-galvanized, with a small amount of galvanizing, only 10-50g/m2, and its corrosion resistance is much worse than that of hot-dip galvanized pipe. In order to ensure quality, most of the regular galvanized pipe manufacturers do not use electro-galvanizing (cold plating). Only small companies with small equipment and old equipment use electro-galvanized steel, of course, their prices are relatively cheaper. At present, the Ministry of Construction has officially laid down the cold-galvanized pipe with backward technology, and the cold-galvanized pipe is not allowed to be used as water and gas pipe in the future. The galvanized layer of the cold-galvanized steel pipe is an electroplated layer, and the zinc layer and the steel pipe base are separately layered. The zinc layer is thin, and the zinc layer is simply attached to the steel pipe base and is easy to fall off. Therefore, its corrosion resistance is poor. In new homes, the use of cold-galvanized steel pipes as water supply pipes is prohibited.
