After pickling, cleaning, and optionally immersion in a dilute hydrochloric acid solution, steel pipes must be coated with a layer of concentrated hydrochloric acid, zinc chloride aqueous solution, ammonium chloride aqueous solution, or a complex salt aqueous solution of zinc chloride and ammonium chloride before hot-dip galvanizing, followed by drying. Alternatively, the complex salt of zinc chloride and ammonium chloride can be placed directly in a special box on the surface of the molten zinc, so that the steel pipes to be galvanized pass through the molten complex salt layer before entering the zinc liquid. The process of producing galvanized steel pipes using these two solvent application methods is called the solvent method. The former is known as the "dry solvent method" or simply "dry method," while the latter is called the "wet flux method" or simply "wet method."
The purpose of using a solvent is to ensure that when the steel pipe is immersed in hot zinc liquid for galvanizing, the iron matrix on the surface of the steel pipe can react normally with the zinc liquid within a short period of time to form a complete iron-zinc alloy layer. In the "dry method," the solvent film on the surface of the steel pipe can also prevent the metal matrix of the steel pipe from being oxidized.
