Galvanized seamless pipes are pided into hot-dip galvanizing and cold-galvanizing. The hot-dip galvanized steel tube is obtained by reacting a molten metal with an iron matrix to produce an alloy layer, thereby combining the substrate and the plating layer. Hot-dip galvanizing is to pickle the steel pipe first, in order to remove the iron oxide on the surface of the steel pipe, after pickling, it is washed by ammonium chloride or zinc chloride aqueous solution or a mixed aqueous solution of ammonium chloride and zinc chloride, and then fed.
Hot dip plating tank. Hot-dip galvanizing has the advantages of uniform plating, strong adhesion and long service life. The steel pipe matrix and the molten plating solution undergo complex physical and chemical reactions to form a corrosion-resistant structure of a zinc-iron alloy layer. The alloy layer is integrated with the pure zinc layer and the steel pipe base. Therefore, its corrosion resistance is strong.
1. Uniformity of galvanized layer: The steel pipe sample shall be continuously immersed in copper sulfate solution for 5 times without being red (copper plating) 2. Surface quality: the surface of the galvanized steel pipe should have a complete galvanized layer, there must be no black spots and bubbles that are not plated, allowing for a rough surface and local zinc tumors. 3. Weight of galvanized layer: According to the requirements of the purchaser, the galvanized steel pipe can be used for the weight determination of the zinc layer. The average value should be not less than 500g/m2, and any sample should not be less than 480g/m2.
Cold galvanizing is electrogalvanizing. The amount of galvanizing is very small, only 10-50g/m2, and its corrosion resistance is much worse than that of hot-dip galvanized pipe. Regular galvanized pipe manufacturers, in order to ensure quality, most do not use electro-galvanizing (cold plating). Only small companies with small equipment and old equipment use electro-galvanized steel, of course, their prices are relatively cheaper.
At present, the Ministry of Construction has officially laid down the cold-galvanized pipe with backward technology, and the cold-galvanized pipe is not allowed to be used as water and gas pipe in the future. The zinc layer is an electroplated layer, and the zinc layer and the steel pipe matrix are layered independently. The zinc layer is thin, and the zinc layer is simply attached to the steel pipe base and is easy to fall off. Therefore, its corrosion resistance is poor. In new homes, it is forbidden to use cold-galvanized steel pipes as water supply pipes.
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