The valve is the control component in the fluid transmission system, which has the functions of cut-off, regulation, diversion, prevention of countercurrent, pressure stabilization, diversion or overflow pressure relief. There are many kinds and specifications of valves used in fluid control system, from simple stop valve to various valves used in more complex automatic control system.

Valve corrosion is generally understood as the damage of valve metal materials under the action of chemical or electrochemical environment. Since "corrosion" phenomenon occurs in the spontaneous interaction between metal and surrounding environment, how to isolate metal from surrounding environment or use more non-metallic synthetic materials is the focus of anti-corrosion.

The valve body of the valve includes the valve cover, which occupies most of the weight of the valve and is in frequent contact with the medium. Therefore, the selection of the valve is often based on the material of the valve body. The anti-corrosion of valve body mainly depends on the correct selection of materials. Although there are abundant data on corrosion prevention, it is not easy to choose the right one, because the problem of corrosion is very complex. For example, sulfuric acid has great corrosivity to steel when the concentration is low, and passivation film will be produced on steel when the concentration is high, which can prevent corrosion; Hydrogen shows strong corrosion to steel only under high temperature and high pressure. When chlorine is dry, the corrosion performance is not large, but when there is a certain humidity, the corrosion performance is very strong, and many materials can not be used. The difficulty in selecting valve body materials also lies in not only considering the corrosion problem, but also considering the pressure and temperature resistance, whether it is economically reasonable, whether it is easy to purchase and other factors.

There are no more than two forms of corrosion of valve body, 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 less 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. Corrosion resistance: corrosion rate 0.1 to 1.0 mm / year.

5. Poor corrosion resistance: corrosion rate 1.0 to 10 mm / year.

6. Non corrosion resistance: the corrosion rate is greater than 10mm / year.

The second is to take lining measures, such as lead lining, aluminum lining, engineering plastics lining, natural rubber lining and various synthetic rubber lining. If the media conditions permit, this is an economical method. Then, when the pressure and temperature are not high, using non-metal as the main material of the valve can often effectively prevent corrosion. The external surface of the valve is also corroded by the atmosphere. Generally, steel materials are protected by painting.