In order to improve the corrosion resistance of steel pipes, galvanized steel pipes are commonly used. Galvanized steel pipe can be divided into hot-dip galvanizing and cold galvanizing. The hot-dip galvanizing layer is thick, the galvanizing cost is low, and the surface is not very smooth. Oxygen-blowing welded pipe: Used as steel-making oxygen-blowing pipe, generally with small-diameter welded pipe, specifications from 3/8-2 inch eight kinds. Made of 08, 10, 15, 20 or 195-Q235 steel strips, aluminizing is necessary to prevent corrosion.
Most of the old houses used galvanized pipes. The iron pipes used for gas and heating were also galvanized. The galvanized pipes were used as water pipes. After several years, a large amount of rust and dirt were produced in the pipes. The yellow water not only polluted the sanitary ware, but also mixed with bacteria which grew in the unsmooth inner walls. The rust caused the high content of heavy metals in the water and caused serious danger. Harm to human health. In 60s and 70s, the developed countries began to develop new types of pipes and banned galvanized pipes one after another. Four ministries and commissions, such as the Ministry of Construction, have been civilized in banning galvanized pipes since 2000. Since 2000, galvanized pipes have seldom been used in cold water pipes in new residential areas. In some residential areas, galvanized pipes have been used in hot water pipes.
Galvanized steel pipes are separately cold plated and hot plated. The former has been banned and the latter is temporarily promoted by the state.
Hot-dip galvanized pipe
Hot-dip galvanized pipe is to make molten metal and iron matrix reaction to produce alloy layer, so that the substrate and coating combination. Hot-dip galvanizing is to carry out acid cleaning of steel pipes, in order to remove iron oxide on the surface of steel pipes, after acid cleaning, through ammonium chloride or zinc chloride solution or ammonium chloride and zinc chloride mixed solution tank for cleaning, and then into the hot-dip bath. Hot dip galvanizing has the advantages of uniform coating, strong adhesion and long service life.
Cold galvanized pipe
Cold galvanizing is galvanizing, the amount of galvanizing is very small, only 10-50g/m2, its corrosion resistance than hot-dip galvanized pipe is much different. Regular galvanized pipe manufacturers, in order to ensure quality, most of them do not use zinc plating (Leng Du). Only small businesses with obsolete equipment adopt galvanizing, and their prices are relatively cheap. The Ministry of Construction has formally set down the following, the elimination of backward technology of cold galvanized pipes, cold galvanized pipes are not allowed to be used for water, gas pipes.
Hot-dip galvanized steel pipe: The complex physical and chemical reactions between the steel pipe substrate and the molten plating solution result in the formation of a zinc-iron alloy layer with a tight corrosion resistance structure. The alloy layer is integrated with the pure zinc layer and the steel tube substrate. Therefore, its corrosion resistance is strong.
Cold galvanized steel pipe: zinc layer is electroplated layer, zinc layer and steel tube matrix separate layer. The zinc layer is thin, and the zinc layer is simply attached to the steel tube substrate, so it is easy to fall off. Therefore, its corrosion resistance is poor. In new buildings, cold galvanized steel pipes are not allowed to be used as water pipes.