There are many points to choose a valve, in addition to some necessary technical knowledge, there are many other factors affecting it. Let’s take a look at how to look at the valve body material to choose a valve.
The valve body occupies most of the weight of the valve and is in contact with the medium, so when choosing a valve, we still pay more attention to 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.
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 problem of corrosion is very complicated. 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 choosing the valve body material lies in that we should not only consider the corrosion problem, but must also 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.
In addition, the outer surface of the valve is also corroded by the atmosphere, and general steel materials are protected by painting.
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.