The hot-dip galvanized pipe is to make the molten metal react with the iron matrix to form an alloy layer, so that the matrix and the coating are combined. 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 cleaned in a tank of ammonium chloride or zinc chloride aqueous solution or a mixed aqueous solution of ammonium chloride and zinc chloride, and then sent to the steel pipe. in the hot dip bath. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion and long service life. The steel tube substrate and the molten plating solution have complex physical and chemical reactions, forming a corrosion-resistant zinc-iron alloy layer with a tight structure. The alloy layer is integrated with the pure zinc layer and the steel tube substrate. Therefore, it has strong corrosion resistance.
1. Uniformity of galvanized layer: The steel pipe sample shall not turn red (copper-plated color) after being dipped in copper sulfate solution for 5 consecutive times.
2. Surface quality: The surface of the galvanized steel pipe should have a good galvanized layer, and there should be no black spots and bubbles that are not plated, and there should be small rough surfaces and some zinc tumors.
3. Galvanized layer weight: According to the demand of the buyer, the galvanized steel pipe can be used for the measurement of the zinc layer weight.
Cold galvanizing is electric galvanizing, and the amount of galvanizing is very small, as long as 10-50g/m2, its own corrosion resistance is much different than that of hot-dip galvanized pipe. Standard galvanized pipe manufacturers, in order to ensure quality, most do not use electro-galvanized (cold galvanized). As long as those small enterprises with small plans and outdated equipment choose electro-galvanizing, of course their prices are relatively cheap. At present, the Ministry of Construction has officially issued a document to screen cold galvanized pipes with backward technology, and it is forbidden to use cold galvanized pipes for water and gas pipes in the future. The zinc layer is an electroplating layer, and the zinc layer is independently layered with the steel pipe substrate. The zinc layer is thin, and the zinc layer is easily attached to the steel pipe substrate and easily falls off. Therefore, its corrosion resistance is poor. In newly built residences, the use of cold galvanized steel pipes as water supply pipes is prohibited.