Corrosion of valves has always been a big problem in valve maintenance, so let’s share with youCorrosion and protection methods of metal valves:
The valve body of the valve includes the bonnet, which occupies most of the weight of the valve and is in constant contact with the medium. Therefore, the selection of valves often starts from the material of the valve body.
The corrosion of the valve body is nothing more than two forms, namely chemical corrosion and electrochemical corrosion. Its corrosion rate depends on the temperature, pressure, chemical properties of the medium and the corrosion resistance of the valve body material. The corrosion rate can be divided into six grades:
1. Complete corrosion resistance: the corrosion rate is lower than 0.001 mm/year;
2. Extreme corrosion resistance: corrosion rate 0.001 to 0.01 mm/year;
3. Corrosion resistance: corrosion rate 0.01 to 0.1 mm/year;
4. High corrosion resistance: corrosion rate 0.1 to 1.0 mm/year;
5. Poor corrosion resistance: corrosion rate 1.0 to 10 mm/year;
6. No corrosion resistance: the corrosion rate is greater than 10mm/year.
Corrosion of valves is generally understood as the damage of valve metal materials under the action of chemical or electrochemical environments. Since the corrosion phenomenon occurs in the spontaneous interaction between the metal and the surrounding environment, how to isolate the metal from the surrounding environment or use more non-metallic composite materials is the focus of anti-corrosion.
The anti-corrosion of the valve body is mainly the correct selection of materials. Although the anti-corrosion information is very rich, it is not easy to choose the right one, because the corrosion problem is very complicated. For example, sulfuric acid is very corrosive to steel at low concentration, and it will cause steel Passivation film, which can prevent corrosion; hydrogen shows strong corrosion to steel only under high temperature and high pressure, chlorine gas is not very corrosive when it is in a dry state, but it is very corrosive when there is a certain humidity, and many materials cannot be used . The difficulty in selecting valve body materials lies in the fact that we cannot only consider the corrosion problem, but also must consider factors such as pressure and temperature resistance, whether it is economically reasonable, and whether it is easy to purchase. So you have to be careful.
The second is to take lining measures, such as lining lead, lining aluminum, lining engineering plastics, lining natural rubber and various synthetic rubbers, etc. If the medium conditions permit, this is a saving method.
Thirdly, when the pressure and temperature are not high, using non-metal as the main material of the valve can often prevent corrosion very effectively.
Finally, the outer surface of the valve is also corroded by the atmosphere, and general steel materials are protected by painting.
All of the above is the corrosion and protection method of metal valves shared with you today. Hurry up and get up~