The valve is a 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. The valves used in the fluid control system, from the simplest stop valve to the most complex automatic control system, have a wide variety of types and specifications.

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

The valve body, including the valve cover, occupies most of the weight of the valve and is in constant contact with the medium. Therefore, the selection of the valve is often based on the valve body material. Anti-corrosion of valve body mainly depends on the correct selection of materials. Although the data on corrosion prevention is very rich, it is not easy to choose the right one, because the problem of corrosion is very complex. For example, sulfuric acid has great corrosivity on steel at low concentration, and it will produce a passivation film on steel at high concentration, which can prevent corrosion; Hydrogen only shows strong corrosivity to steel at high temperature and high pressure. When chlorine is dry, the corrosivity is not great, but when there is a certain humidity, the corrosivity is very strong, and many materials cannot be used. The difficulty in selecting valve body material is that it is not only necessary to consider the corrosion problem, but also to consider the pressure and temperature resistance, whether it is reasonable economically, and whether it is easy to buy. So you must be careful.

The corrosion of valve body can be divided into 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: 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 10 mm/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 a saving method. In addition, when the pressure and temperature are not high, using non-metal as the main material of valve can often effectively prevent corrosion. The external surface of the valve is also subject to atmospheric corrosion. Generally, steel materials are protected by painting.