Valve corrosion, usually understood as the valve metal material under the chemical or electrochemical environment suffered damage. Since "corrosion" occurs in the spontaneous interaction between metal and the surrounding environment, how to separate the metal from the surrounding environment or use more non-metallic synthetic materials is the key point of anti-corrosion. Valve body (including valve cover), accounting for most of the weight of the valve, but also in regular contact with the medium, so the choice of valve often starting from the valve body material. Valve body corrosion no more than two forms, namely chemical corrosion and electrochemical corrosion. Its corrosion rate depends on the medium temperature, pressure, chemical properties and corrosion resistance of the valve body material. Corrosion rate can be divided into six grades: 1. Corrosion resistance: Corrosion rate is lower than 0.001mm / year 2. Corrosion resistance: Corrosion rate 0.001 to 0.01mm / year 3. Corrosion resistance: Corrosion rate 0.01 to 0.1mm / year 4 , Still corrosion: corrosion rate of 0.1 to 1.0 mm / year 5, poor corrosion resistance: corrosion rate of 1.0 to 10 mm / year 6, non-corrosion corrosion: corrosion rate greater than 10 mm / year body corrosion, mainly the correct choice material. Although the anti-corrosion information is very rich, but it is still not easy to choose the right thing, because the problem of corrosion is very complex, such as sulfuric acid in the low concentration of steel is very corrosive, high concentration, then the steel production Passivation film, can be anti-corrosion; hydrogen only shows high corrosion resistance to steel under high temperature and pressure, chlorine corrosion performance is not large in dry state, and a certain humidity, the corrosion performance is strong, many materials can not be used . The difficulty of choosing the valve body material lies in that it can not only consider the corrosion problem, but also must consider the ability of pressure and temperature resistance, economically reasonable and easy to purchase and other factors. So you must be careful.