Today, hot-dip galvanized steel pipes are a common type of fire protection pipes, playing an irreplaceable role in the fire safety industry. Why can't hot-dip galvanized pipes be replaced by cheaper welded pipes or cold-galvanized pipes?
Hot-dip galvanizing was invented in the mid-18th century, evolving from the hot-dip tinning process, with a history of over 300 years. To this day, hot-dip galvanizing remains a widely used and effective processing method among steel corrosion prevention techniques.
The fundamental principle of galvanized steel protection lies in: besides forming an outer coating that isolates the steel pipe from corrosion by air and moisture, it also leverages the fact that iron has a higher electronegativity than zinc. By preferentially oxidizing the zinc layer, it sacrifices the zinc layer to protect the inner steel. As a result, the corrosion resistance of ordinary welded pipes cannot compare. Even steel that has undergone corrosion prevention treatments such as oiling and painting cannot match the corrosion resistance of hot-dip galvanized pipes.
The zinc coating of hot-dip galvanized pipes is a shell that covers the surface of the steel pipe after immersion, whereas cold-galvanized pipes have a layer of film formed through electrolytic reactions. Therefore, the thickness of the zinc coating on hot-dip galvanized steel pipes is significantly greater than that of cold-galvanized pipes. Based on the fundamental principle of galvanized steel protection, we understand that thicker zinc coatings with more zinc provide better protection for steel. Consequently, hot-dip galvanized steel pipes with significantly thicker zinc coatings exhibit corrosion resistance that is dozens of times greater than cold-galvanized pipes.
Due to the same reason, the coating of hot-dip galvanized pipes is dense, and the adhesion of the zinc coating is better than that of cold-galvanized pipes. High adhesion means that the zinc coating is less likely to be damaged due to impact and friction during transportation.
Hot-dip galvanized steel pipes are immersed in a galvanizing bath during manufacturing, ensuring that all exposed inner and outer surfaces are coated with zinc. In contrast, cold-galvanized steel pipes are typically made by rolling and welding a piece of pre-galvanized steel plate. As a result, the weld seams of these pipes lack the protection of a zinc coating.
Therefore, to ensure safer and more durable fire protection pipes, hot-dip galvanized steel pipes are the preferred choice.
