Galvanized steel pipes are divided into cold galvanized steel pipes and hot-dip galvanized steel pipes. Cold galvanized steel pipes have been banned, while the latter is still temporarily recommended for use by the state. In the 1960s and 1970s, developed countries internationally began to develop new types of pipes and gradually banned the use of galvanized pipes. The Ministry of Construction of China and three other ministries also issued a document clearly stating that galvanized pipes are prohibited for use as water supply pipes starting from 2000. Cold water pipes in new residential areas rarely use galvanized pipes anymore, although some residential areas still use galvanized pipes for hot water pipes. Hot-dip galvanized steel pipes are widely used in fire protection, electricity, and on highways.
Galvanized Steel Pipe Product Applications
Hot-dip galvanized steel pipes are widely used in construction, machinery, coal mining, chemical, power, railway vehicles, automotive industry, highways, bridges, containers, sports facilities, agricultural machinery, petroleum machinery, prospecting machinery, greenhouse construction, and other manufacturing industries.
Galvanized steel pipes have a surface with a hot-dip galvanized or electro-galvanized layer on welded steel pipes. Galvanization can increase the corrosion resistance of steel pipes and extend their service life. The uses of galvanized pipes are extensive, including not only as pipeline pipes for water, gas, oil, and other general low-pressure fluids, but also as oil well pipes and oil pipelines in the petroleum industry, especially for offshore oil fields, pipes for oil heaters, condensers, coolers, and coal distillation oil exchangers in chemical coking equipment, as well as pipes for bridge piles, and support frames for mine tunnels.
Hot-dip galvanized steel pipes
Hot-dip galvanized steel pipes are produced by reacting molten metal with an iron substrate to form an alloy layer, thereby combining the substrate and the coating. Hot-dip galvanizing involves first pickling the steel pipes to remove iron oxide from the surface. After pickling, the pipes are cleaned in a bath of ammonium chloride or zinc chloride solution, or a mixture of both, before being immersed in the hot-dip galvanizing tank. Hot-dip galvanized steel pipes have the advantages of uniform coating, strong adhesion, and long service life. During the hot-dip galvanizing process, the steel pipe substrate undergoes complex physical and chemical reactions with the molten zinc bath, forming a tightly structured zinc-iron alloy layer that is resistant to corrosion. This alloy layer, along with the pure zinc layer and the steel pipe substrate, integrates into a single unit, thus providing strong corrosion resistance.
Cold-dip galvanized steel pipes
Cold-dip galvanized steel pipes, also known as electro-galvanized pipes, have a much lower zinc coating weight, ranging from 10 to 50 grams per square meter. Their corrosion resistance is significantly less than that of hot-dip galvanized pipes. Reputable galvanized pipe manufacturers, to ensure quality, generally do not use electro-galvanizing (cold plating). Only small enterprises with outdated equipment tend to use electro-galvanizing, and their prices are relatively cheaper. The Ministry of Construction has officially issued a document to phase out the technologically backward cold-dip galvanized pipes, prohibiting their use for water and gas pipes. The zinc coating on cold-dip galvanized steel pipes is an electroplated layer, which is independently layered from the steel pipe substrate. The zinc layer is thin and simply adheres to the steel pipe substrate, making it prone to peeling off. Therefore, its corrosion resistance is poor. In new residential construction, the use of cold-dip galvanized steel pipes as water supply pipes is prohibited.
National Standards and Dimensions for Galvanized Steel Pipes
GB/T3091-2015 Welded Steel Pipes for Low-Pressure Fluid Delivery
GB/T13793-2016 Straight Seam Electric-Welded Steel Pipes
GB/T21835-2008 Dimensions and Unit Length Weight of Welded Steel Pipes
