Anticorrosion of metal valves
Electrochemical corrosion corrodes metals in various forms. It not only acts between two metals, but also generates potential differences due to the concentration difference of the solution, the concentration of oxygen, and the slight difference in the internal structure of the metal, which aggravates the corrosion. In order to achieve the purpose of anti-corrosion of metal valves, one is to eliminate electrochemical corrosion; the other is to make a passivation film on the metal surface when electrochemical corrosion cannot be eliminated; the third is to use non-metallic materials without electrochemical corrosion. instead of metal materials.
(1) Select valve material according to medium
The corrosion of the medium is very complicated. Even if the valve material used in the same medium is the same, the concentration, temperature and pressure of the medium are different, and the medium corrodes the material differently. The corrosion of lead by sulfuric acid with a small concentration is very small. When the concentration exceeds 96%, the corrosion increases sharply. On the contrary, carbon steel has the most serious corrosion when the concentration of sulfuric acid is about 50%, and when the concentration increases to more than 60%, the corrosion decreases sharply. Stainless steel has only good corrosion resistance to dilute nitric acid, but the corrosion is aggravated in more than 95% concentrated nitric acid.
（2）Use non-metallic materials
Non-metallic materials have excellent corrosion resistance. As long as the operating temperature and pressure of the valve meet the requirements of non-metallic materials, it can not only solve the problem of corrosion resistance, but also save precious metals. The valve body, bonnet, lining, sealing surface and other common metal materials are made of common metal materials, and the chamber gasket and packing are mainly made of non-metallic materials. Use plastics such as polytetrafluoroethylene and chlorinated polyether, as well as natural rubber, neoprene, nitrile rubber, etc. as the lining of the valve, while the valve body and valve cover are generally made of cast iron and carbon steel, which not only guarantees It improves the strength of the valve and ensures that the valve is not corroded. The pinch valve is also designed based on the excellent corrosion resistance and excellent variability of rubber. Now more and more plastics such as nylon or polytetrafluoroethylene are used, and various sealing surfaces and sealing rings are made of natural rubber and synthetic rubber, which are used on various types of valves. These non-metallic materials used as sealing surfaces , not only good corrosion resistance, but also good sealing performance, especially suitable for use in media with particles. The emergence of flexible graphite has brought non-metallic materials into the high-temperature field, solving the long-term problem of packing and gasket leakage, and flexible graphite is a good high-temperature lubricant.
(3) Spray paint
Coatings are also non-metallic materials, which are usually made of synthetic resin, rubber slurry, etc., and cover the metal surface to isolate the medium and the atmosphere to achieve the purpose of anti-corrosion. Coatings are mainly used in water, salt water, seawater, atmosphere and other environments that are not very corrosive. Anti-corrosion paint is often painted on the inner wall of the valve to prevent the corrosion of water, air and other media. The paint is mixed with different colors to represent the material used in the valve. The valve is sprayed with paint, generally once every six months to a year.