Hot-dip galvanizing is a process in which a metal material or part with a clean surface is immersed in a molten zinc solution, and a layer of metal zinc is formed on the surface through a physical and chemical reaction at the interface. Hot-dip galvanizing, also known as hot-dip galvanizing and hot-dip galvanizing, is an effective metal anti-corrosion method, which is mainly used for surface anti-corrosion of metal structures, facilities and materials in various industries. So what are the characteristics of hot-dip galvanized seamless steel pipe?
1. The gray patches of different sizes on the surface of galvanized seamless steel pipe are the color difference of galvanizing, which is a difficult problem in the current galvanizing industry, mainly related to the trace elements contained in the steel pipe itself and the components in the zinc bath. The stain does not affect the anti-corrosion performance of the steel pipe, only the difference in appearance.
2. There are gradually obvious raised marks on the surface of each galvanized seamless steel pipe, which are all zinc, which is formed by cooling and solidification of the zinc liquid flowing down the pipe wall after the galvanized seamless steel pipe is taken out of the zinc pot.
3. There are traces of grinding and painting near both ends of each galvanized seamless steel pipe. When hot-dip galvanizing, the pipe should be fixed on a special steel frame and soaked in zinc solution together with the steel frame. There will be marks on the fixed place after galvanizing. For aesthetics, it needs to be sanded and sprayed with zinc.
4. Some customers will use groove connection in the process of using galvanized seamless steel pipe to press groove. Due to the thick zinc layer of the hot-dip galvanized seamless steel pipe, under the action of destructive external force, part of the galvanized layer will crack and peel off, which has nothing to do with the quality of the galvanized seamless steel pipe itself.
5. Some customers will react that there is a yellow liquid on the galvanized seamless steel pipe (this liquid is called passivation liquid), which can passivate the metal surface. Generally used for post-plating treatment of galvanized, cadmium and other coatings. The purpose is to form a surface state on the surface of the coating that can prevent the normal reaction of the metal, improve its corrosion resistance, and increase the aesthetics of the product. It can effectively improve the corrosion resistance of the steel pipe and prolong the service life of the workpiece.
The protection effect of hot-dip galvanized layer on seamless steel pipe is much better than that of paint or plastic layer. In the process of hot-dip galvanizing, zinc diffuses with the steel to form a zinc-iron intermetallic compound layer, that is, an alloy layer. The alloy layer is metallurgically bonded to steel and zinc, which is stronger than the bond between paint and steel. The hot-dip galvanized layer is exposed to the atmospheric environment and does not fall off for decades until it is completely corroded naturally.
The hot-dip galvanizing technology of seamless steel pipe can generally be divided into dip plating and blowing plating:
1. Dip plating. Cool with water directly after soaking. The average thickness of the zinc layer is greater than 70 microns, so the cost of galvanizing is high, and the amount of zinc is large. In the normal atmospheric environment for more than 50 years, there are obvious traces of zinc flow, and the longest seamless steel pipe can be plated to 16m.
2. Blow plating. After galvanizing, the outside is blown and the inside is cooled. The average thickness of the zinc layer is greater than 30 microns, the cost is low, and the zinc consumption is small. After more than 20 years of use in normal atmospheric environment, almost no trace of zinc liquid can be seen. General blown zinc production line 6-9m.