Hot-dip galvanized steel pipe is widely used in manufacturing industries such as construction, machinery, coal mining, chemicals, electric power, railway vehicles, the automotive industry, highways, bridges, containers, sports facilities, agricultural machinery, petroleum machinery, prospecting machinery, and greenhouse construction.

Galvanized steel pipe is a welded steel pipe with a hot-dip or electroplated zinc coating. Galvanizing increases the pipe's corrosion resistance and extends its service life. Galvanized pipe has a wide range of applications. In addition to being used as line pipe for conveying general low-pressure fluids such as water, gas, and oil, it is also used in the petroleum industry, especially for oil well pipes and oil pipelines in offshore oil fields; in oil heaters, condensate coolers, and coal distillation and washing oil exchangers in chemical coking equipment; and in pier piles and support frames for mine tunnels.

Hot-dip galvanized pipes are produced by reacting molten metal with an iron substrate to form an alloy layer, thus bonding the substrate and coating. Hot-dip galvanizing begins with pickling the steel pipe to remove iron oxide from the surface. After pickling, the pipe is cleaned in an aqueous solution of ammonium chloride, zinc chloride, or a mixture of ammonium chloride and zinc chloride before being placed in a hot-dip coating tank. Hot-dip galvanizing offers advantages such as uniform coating, strong adhesion, and a long service life. The hot-dip galvanized steel pipe substrate undergoes complex physical and chemical reactions with the molten plating solution, forming a corrosion-resistant, compact zinc-iron alloy layer. This alloy layer is integrated with the pure zinc layer and the steel pipe substrate, resulting in superior corrosion resistance.

Cold-Dip Galvanized Pipes

Cold-dip galvanized pipes are electroplated. The zinc coating is very low, only 10-50g/m². Their corrosion resistance is significantly lower than that of hot-dip galvanized pipes. To ensure quality, reputable galvanized pipe manufacturers generally avoid electroplating (cold galvanizing). Only small businesses with outdated equipment use electroplating, which, of course, offers a relatively lower price. The Ministry of Construction has officially eliminated cold-dip galvanized pipes, a technologically backward process, and prohibits their use for water and gas pipes. The zinc coating on cold-dip galvanized steel pipes is electroplated, separated from the steel base. The zinc layer is thin and simply adheres to the steel base, making it easily detachable. Consequently, its corrosion resistance is poor. Cold-dip galvanized steel pipes are prohibited for water pipes in newly built residential buildings.