Corrosion on valves can be considered that metal materials of vales are damaged due to chemical or electrochemical environment. Corrosion is caused by reaction between metal and surrounding environment. For this, separating metal form surrounding environment and using more non-metal synthetic materials are the key points of corrosion resistance.
Body of valves including bonnet accounts most of valves, and often contacts with media. So materials of body should be taken into consideration when choosing valves.
Corrosion on body is classified into two kinds: chemical corrosion and electrochemical corrosion. Corrosion rate depends on temperature, pressure and chemical properties of media and corrosion resistance capacity of body materials.
Corrosion resistance of body is mainly up to using materials. Although corrosion resistance materials are quite varied, choosing appropriate materials is not easy due to complicated corrosion. For example, sulfuric acid having low concentration have strong corrosion to steel materials while can cause a layer of passive film on steel materials to corrosion resistance, for high concentration. Besides corrosion, high pressure and high temperature resistance and economical conservation also should be considered.
Lining is also available such as lining lead, aluminum, engineering plastics, natural rubber and other synthetic. Lining is a kind of economical conservations, if it is permitted.
Under low pressure or temperature, using non-metal as main materials of valves can also prevent corrosion effectively.
Moreover, surface of body is corroded by air. In general, steel material is painted for protection.
Apr 16,2015
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