Corrosion and protection methods of the hottest va

Corrosion and protection methods of valve body

corrosion of valve is usually understood as the damage of valve metal materials under the action of chemical or electrochemical environment. Since the phenomenon of "corrosion" 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

the valve body (including the bonnet) of the valve occupies most of the weight of the valve and is in frequent contact with the medium, so the selection of the valve is often based on the material of the valve body

there are no more than two forms of corrosion of the valve body, namely chemical corrosion and electrochemical corrosion. Its corrosion rate depends on the temperature, pressure, chemical properties and 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. Extremely corrosion resistant: the corrosion rate is 0.001 to 0. According to the performance and requirements of the flexible packaging film to be tested 01 mm/year press the "brake" button

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 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 makes steel produce passive film 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 after 6 days of intense work, the corrosion performance is not great, but when there is a certain humidity, the corrosion performance is very strong, and many materials cannot be used. The difficulty in selecting valve body materials lies in not only considering corrosion, but also considering pressure and temperature resistance, whether it is economically reasonable, whether it is easy to purchase and other factors. So we must be careful

the second is to take lining measures, such as lining with lead, aluminum, engineering plastics, natural rubber and various synthetic rubber. 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 effectively prevent corrosion

in addition, the external surface of the valve is also corroded by the atmosphere, and generally steel materials are protected by painting. (end)