Galvanized steel pipes are classified into two types: hot-dip galvanized steel pipe and cold-galvanized steel pipe. Cold-galvanized steel pipe, also known as electro-galvanized steel pipe, has a low zinc content, approximately 10g to 20g per square meter, resulting in inferior corrosion resistance compared to hot-dip galvanized steel pipe. The latter boasts superior corrosion resistance. Beyond that, what are the other differences between the two?
Differences Between Hot-dip and Cold-galvanized Steel Pipes
First, they differ significantly in their production processes. The zinc used in hot-dip galvanizing is obtained at a temperature ranging from 450°C to 480°C, whereas the zinc in cold-galvanized steel pipes is applied through an electroplating process at room temperature.
Second, there is a substantial distinction in the thickness of the zinc coating. Hot-dip galvanized steel pipes have a thicker zinc coating than cold-galvanized ones.
Third, they vary in surface smoothness. The surface of cold-galvanized steel pipes is significantly rougher than that of hot-dip galvanized pipes.
Fourth, there is a considerable price difference. Manufacturers typically avoid using electroplating for hot-dip galvanized pipes to ensure quality. In contrast, smaller enterprises with outdated equipment often resort to electroplating, making cold-galvanized steel pipes less expensive.
Fifth, hot-dip galvanized pipes are fully coated with zinc, whereas cold-galvanized pipes are only coated on one side.
Sixth, their adhesion properties are distinct. Cold-galvanized pipes exhibit inferior adhesion compared to hot-dip galvanized pipes due to the thin and easily detachable zinc layer, which is simply attached to the steel substrate surface independently.
Cold-galvanized pipes undergo electroplating, resulting in zinc coating only on the outer surface, not the inner wall. In contrast, hot-dip galvanized pipes undergo hot-dip galvanizing, ensuring zinc coating on both inner and outer walls. Regulations prohibit the use of cold-galvanized pipes for gas and water pipelines due to their poor corrosion resistance, easy zinc peeling, and potential safety hazards.
In summary, the key differences lie in zinc thickness, surface smoothness, price, corrosion resistance, and adhesion properties.
