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The valve shell includes the valve body, valve cover, etc., which account for most of the weight of the valve and are in constant contact with the medium. Therefore, the selection of valves often starts with the material of the valve shell.

There are two forms of valve body corrosion, 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 shell material. The corrosion rate is divided into 6 levels:

a. Complete corrosion resistance - <0.001mm/year;

b. Extreme corrosion resistance - 0.001~0.01mm/year;

c. Corrosion resistance -0.01~0.1mm/year;

d. Moderate corrosion resistance - 0.1~1.0mm/year;

e. Poor corrosion resistance - 1.0~10mm/year;

f. No corrosion resistance - > 10mm/year.

The anti-corrosion of the valve body mainly depends on the correct selection of materials. Although there are many anti-corrosion materials, it is not easy to choose properly, because the problem of corrosion is very complicated. For example, sulfuric acid is very corrosive to steel when the concentration is low, and it will cause a passivation film on the steel when the concentration is high. , can prevent corrosion, etc.;

The second is to take lining measures, such as lining lead, aluminum, engineering plastics, natural rubber and various synthetic rubbers. 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.