Prevention and Treatment of Valve Corrosion
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There are two forms of corrosion for valve bodies, namely chemical corrosion and electrochemical corrosion. The corrosion rate of the valve body is determined by the temperature, pressure, chemical properties of the medium and the corrosion resistance of the valve body material. The corrosion rate can be classified into six grades:
1. Completely corrosion-resistant: Corrosion rate less than 0.001 mm/year;
2. Highly corrosion-resistant: Corrosion rate 0.001 to 0.01 mm/year;
3. Corrosion-resistant: Corrosion rate 0.01 to 0.1 mm/year;
4. Moderately corrosion-resistant: Corrosion rate 0.1 to 1.0 mm/year;
5. Poor corrosion resistance: Corrosion rate 1.0 to 10 mm/year;
6. Not corrosion-resistant: Corrosion rate greater than 10 mm/year.
How to prevent valve corrosion?
The prevention of valve body corrosion mainly lies in the correct selection of materials. Although there is a wealth of information on corrosion prevention, it is still not an easy task to make the right choice because the issue of corrosion is very complex. For example, sulfuric acid has a strong corrosive effect on steel at low concentrations, but at high concentrations, it forms a passive film on the steel surface, which can prevent corrosion. Hydrogen only shows strong corrosive effects on steel at high temperatures and pressures. Chlorine gas has little corrosive effect when it is dry, but it has a strong corrosive effect when it has a certain humidity. Many materials cannot be used. The difficulty in choosing valve body materials lies in the fact that one cannot only consider the corrosion issue, but also must take into account the pressure and temperature resistance, economic rationality, and ease of purchase and other factors. Therefore, one must be careful.
Secondly, lining measures can be taken, such as lining with lead, aluminum, engineering plastics, natural rubber, and various synthetic rubbers. If the medium conditions permit, this is a cost-effective method.
Thirdly, in cases where the pressure and temperature are not high, using fluorine-lined valve body materials can often effectively prevent corrosion.
Fourthly, the outer surface of the valve body is also subject to atmospheric corrosion. Generally, steel materials are protected by painting.
