Galvanized steel pipes are composed of steel pipes (including welded and seamless pipes) and galvanized coatings. It includes cold galvanized steel pipes and hot galvanized steel pipes.
Hot-dip galvanized pipe is to make molten metal react with iron matrix to produce an alloy layer, so that the matrix and coating can be combined. In order to remove the iron oxide on the surface of steel pipes, the first process of hot-dip galvanizing is pickling steel pipes. after pickling, the pipes are cleaned through ammonium chloride or zinc chloride aqueous solution or ammonium chloride and zinc chloride mixed aqueous solution tank and then sent into the hot-dip galvanizing tank. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion, and long service life. Complex physical and chemical reactions occur between the hot-dip galvanized steel tube matrix and the molten plating solution, resulting in a zinc-iron alloy layer with a close corrosion resistance structure. The alloy layer is integrated with a pure zinc layer and steel tube matrix, so it has strong corrosion resistance.
Cold galvanized pipe is electric galvanized pipe, the content of zinc is very small, only 10-50g/m2, its corrosion resistance is much different than hot galvanized pipe. Regular galvanized pipe manufacturers, in order to ensure the quality, do not use electric galvanizing (cold plating). Only small businesses with obsolete equipment use it, and of course, their prices are relatively cheap. The galvanized layer of cold galvanized steel pipe is an electroplating layer, and the zinc layer is separately stratified with the steel pipe matrix. The zinc layer is thin, and the zinc layer simply adheres to the steel tube matrix, which is easy to fall off. Therefore, its corrosion resistance is poor. The Ministry of Construction of China has officially decided to eliminate backward cold galvanized pipes and prohibit the use of cold galvanized pipes as water and gas pipes.
Galvanized pipes are widely used in the petroleum industry, especially in offshore oil fields, oil wells, pipelines, oil heaters, condensation coolers, coal distillation oil washer exchangers, trestle pipe piles and support pipes for mine tunnels.
- API SPEC 5L — Specification for Line Pipe
- ASTM A53/A53M — Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless
- ASTM A500 — Standard Specification for Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes
- BS 1387 — Specification for screwed and socketed steel tubes and tubulars and for plain end steel tubes suitable for welding or for screwing to BS 21 pipe threads
- BS 1139 — Metal scaffolding. Specification for prefabricated mobile access and working towers
- EN 39 — Loose steel tubes for tube and coupler scaffolds
- EN 10255 — Non-alloy steel tubes suitable for welding and threading.
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