Galvanized steel pipes, steel types, galvanized steel pipes are divided into cold galvanized steel pipes and hot-dip galvanized steel pipes.
Hot dip galvanized pipe
Hot dip galvanized pipes produce an alloy layer by reacting molten metal with an iron substrate, thereby bonding the substrate and coating together. Hot dip galvanizing is the process of first pickling steel pipes. In order to remove iron oxide from the surface of the steel pipes, after pickling, they are cleaned in an ammonium chloride or zinc chloride aqueous solution or a mixed ammonium chloride and zinc chloride aqueous solution tank, and then sent to a hot-dip galvanizing tank. Hot dip galvanizing has the advantages of uniform coating, strong adhesion, and long service life. The hot-dip galvanized steel pipe substrate undergoes complex physical and chemical reactions with the molten plating solution, forming a corrosion-resistant and tightly structured 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 pipes are electroplated with zinc, with a very small amount of zinc plating, only 10-50g/m2. Their corrosion resistance is much different from that of hot-dip galvanized pipes. Legitimate galvanized pipe manufacturers, in order to ensure quality, mostly do not use electroplating (cold plating). Only small enterprises with small scale and outdated equipment adopt electroplating, and of course, their prices are relatively cheaper. The Ministry of Construction has officially announced the elimination of technologically outdated cold galvanized pipes and prohibits the use of cold galvanized pipes as water and gas pipes. The galvanized layer of cold galvanized steel pipe is an electroplating layer, and the zinc layer is independently layered with the steel pipe substrate. The zinc layer is relatively thin and easily adheres to the steel pipe substrate, making it prone to detachment. Therefore, its corrosion resistance is poor. Cold galvanized steel pipes are prohibited from being used as water supply pipes in newly constructed residential buildings.
