Galvanized seamless steel pipe is hot-dip galvanized, so the amount of zinc plating is very high, the average thickness of zinc coating is more than 65 microns, and its corrosion resistance is much different than that of hot-dip galvanized pipe. The regular galvanized pipe manufacturer can use cold galvanized pipe as water and gas pipe. The zinc coating of cold galvanized steel pipe is electroplated layer, and the zinc layer is separated from the steel pipe substrate. The zinc layer is thin and easy to fall off because it is attached to the steel pipe substrate. Therefore, its corrosion resistance is poor. It is forbidden to use cold galvanized steel pipe as water supply steel pipe in new residential buildings.