Galvanized pipes can be categorized into hot-dip galvanized steel pipes and cold-galvanized steel pipes, with the latter gradually being phased out.
Hot-Dip Galvanized Steel Pipes
Hot-dip galvanizing involves reacting molten metal with an iron matrix to produce an alloy layer, thereby integrating the matrix and the coating. The manufacturing process of hot-dip galvanized pipes begins with pickling the steel pipes to remove iron oxide from their surfaces. After pickling, the pipes are cleaned in a water solution tank containing ammonium chloride, zinc chloride, or a mixture of both, and then fed into a hot-dip galvanizing tank.
Hot-dip galvanized steel pipes undergo complex physical and chemical reactions between the steel matrix and the molten galvanizing solution, forming a corrosion-resistant, tightly structured zinc-iron alloy layer. This alloy layer merges seamlessly with the pure zinc layer and the steel matrix, imparting the pipes with advantages such as uniform coating, strong adhesion, and long service life.
Cold-Galvanized Steel Pipes
Cold galvanizing, also known as electro-galvanizing, results in a minimal galvanizing amount of only 10-50g/m2, significantly inferior in corrosion resistance to hot-dip galvanized pipes. To ensure quality, most reputable galvanized pipe manufacturers refrain from using electro-galvanizing (cold galvanizing). Only small-scale enterprises with outdated equipment adopt this method, often offering pipes at relatively lower prices. The zinc layer of cold-galvanized steel pipes is independently layered on the steel matrix. Due to its thinness, the zinc layer simply adheres to the steel matrix and is prone to peeling off, leading to poor corrosion resistance. Therefore, cold-galvanized steel pipes have been banned from use as water and gas supply pipes in newly constructed residences.
Production Process of Galvanized Pipes
The specific production process of galvanized steel pipes is confidential among manufacturers. However, a general outline can be provided: a. Round steel preparation; b. Heating; c. Hot-rolling and piercing; d. Cutting the head; e. Pickling; f. Grinding; g. Lubricating; h. Cold rolling; i. Degreasing; j. Solution heat treatment; k. Straightening; l. Cutting pipes; m. Re-pickling; n. Final inspection.
