Hot-dipped galvanized pipe, improving the corrosion resistance of steel pipe to the general steel pipe is galvanized. Galvanized steel pipe is divided into hot dipped galvanized and electrogalvanized.

Two types of galvanizing include hot dipped galvanizing and electrogalvanizing. The former has a thick zinc layer, while the latter has low cost and a less smooth surface.

Hot dipped galvanized pipe is the reaction of molten metal with iron matrix to produce alloy layer, so that the matrix and the coating are combined. Hot dip galvanized is to first pickling the steel pipe, in order to remove the iron oxide on the surface of the steel pipe, after pickling, through ammonium chloride or zinc chloride aqueous solution or ammonium chloride and zinc chloride mixed aqueous solution tank for cleaning, and then into the hot dip plating tank. Hot dip galvanized has the advantages of uniform coating, strong adhesion and long service life. Complex physical and chemical reactions occur between the steel tube substrate and the molten bath to form a tight zinc-iron alloy layer with corrosion resistance. The alloy layer is integrated with the pure zinc layer and the steel pipe matrix. Therefore, its corrosion resistance is strong.

1.The uniformity of the galvanized layer: the steel pipe sample in the copper sulfate solution continuous impregnation 5 times shall not turn red (copper plating color).

2.Surface quality: the surface of galvanized steel pipe should have a complete galvanized layer, no unplated black spots and bubbles exist, allowing a small rough surface and local zinc tumor.

3.Galvanized layer weight: according to the requirements of the clients, galvanized steel pipe can be measured for zinc layer weight, the average value should not be less than 500g/㎡, of which any sample shall not be less than 480g/㎡.

Cold galvanized pipe

Cold galvanized is electrogalvanizing, grams of zinc per item is very small, only 10-50g/㎡, its own corrosion resistance is much different than hot galvanized. Regular galvanized pipe manufacturers, in order to ensure quality, most of them don’t use electrogalvanizing (cold plating). Only those small enterprises with obsolete equipment use electrogalvanizing, of course, the price is relatively cheap. The Ministry of Construction has formally announced the elimination of cold galvanized pipes with backward technology, and it is not allowed to use cold galvanized pipes as water and gas pipes in the future. The zinc layer is an electric coating, and the zinc layer is independently layered with the steel pipe matrix. The zinc layer is thin, and the zinc layer is simply attached to the steel tube matrix and easy to fall off. Therefore, its corrosion resistance is poor. In new residential buildings, it is prohibited to use cold galvanized steel pipes as water supply pipes.

Application

The kind of iron pipe used for gas, greenhouses, heating , it is also called galvanized pipe. Galvanized pipe as a water pipe, it produces a lot of rust and scale,the flowing sewage not only pollutes sanitary ware, but also cotains bacteria that are not smooth inside wall, corrosion causes the heavy metal content in the water is too high, seriously endangering human health. In the 1960s and 1970s, the developed countries in the world began to develop new types of pipes and gradually banned galvanized pipes. The Ministry of Construction of China and other four ministries and commissions have also issued document to prohibit galvanized pipes from 2000, in some communities, the cold water pipes have rarely used galvanized pipes, and in some other new communities the hot water pipes use galvanized pipes.