Measures to prevent corrosion of valve body
The corrosion of the valve is usually understood as the damage of the metal material of the valve under the action of chemical or electrochemical environment. 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 synthetic materials is the focus of anti-corrosion.
Valve body (including the valve cover), occupy most of the weight of the valve, but also in regular contact with the medium, so the selection of the valve, often starting from the body material.
The corrosion of the valve body is no 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. Corrosion rate can be divided into six
1. Complete corrosion resistance: the corrosion rate is less than 0.001mm/year
2. Extremely corrosion resistant: corrosion rate 0.001 to 0.01mm/year
3. Corrosion resistance: corrosion rate 0.01 to 0.1mm/year
4. Still corrosion resistant: corrosion rate 0.1 to 1.0mm/year
5. Poor corrosion resistance: corrosion rate 1.0 to 10mm/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 still not easy to choose it properly, because the corrosion problem is very complicated. For example, sulfuric acid has great corrosion to steel when the concentration is low, and when the concentration is high, it makes steel produce passivation film, which can prevent corrosion. Hydrogen only shows strong corrosion to steel at high temperature and high pressure, and chlorine has little corrosion performance when it is in a dry state, when there is a certain humidity, the corrosion performance is very strong, and many materials can not be used. The difficulty of selecting the valve body material is that it can not only consider the corrosion problem, but also consider the pressure and temperature resistance, whether the economy is reasonable, whether it is easy to buy and other factors. So it must be attentively.