Hot-dip galvanized pipes are produced by causing the molten metal to react with the iron substrate to form an alloy layer, thereby combining the substrate with the coating. The hot-dip galvanizing process involves first acid pickling the steel pipe to remove iron oxide from the surface. After pickling, the pipe is cleaned in a bath of ammonium chloride or zinc chloride solution, or a mixture of both. It is then immersed in a hot dip galvanizing bath. Hot-dip galvanized pipes offer advantages such as even coating, strong adhesion, and long service life. The substrate of hot-dip galvanized steel pipes undergoes complex physical and chemical reactions with the molten coating to form a tightly structured, corrosion-resistant zinc-iron alloy layer. This alloy layer integrates with the pure zinc layer and the steel pipe substrate, thereby enhancing its corrosion resistance.

Cold galvanized pipe

Cold galvanized pipes, also known as electro-galvanized pipes, have a very thin zinc coating, only 10-50g/m2, which is significantly less corrosion-resistant than hot-dip galvanized pipes. Reputable galvanized pipe manufacturers generally do not use electro-galvanized (cold galvanizing) to ensure quality. Only small-scale, outdated equipment firms opt for electro-galvanizing, and naturally, their prices are more competitive. The Ministry of Construction has officially decreed the elimination of outdated cold galvanized pipe technology and prohibits the use of cold galvanized pipes for water and gas pipelines. The zinc coating on cold galvanized steel pipes is an electroplated layer, with the zinc layer and the steel pipe base forming separate layers. The zinc layer is thin and simply adheres to the steel pipe base, 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 new residential buildings.