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Cause and Effect of Corrosion of Pneumatic Ball Valves (Part 1)

 Valve corrosion form: The corrosion of metal is mainly caused by chemical corrosion and electrochemical corrosion. The corrosion of aerodynamic ball valve is generally caused by direct chemical and physical damage.
1. The chemical corrosion of the surrounding medium directly acts on the metal without destroying the current, so as to destroy it, such as high temperature dry gas and non-electrolytic solution to the metal.
2. Electrochemical corrosion
The contact between the metal and the electrolyte produces electron flow, which destroys itself during electrochemical action. This is the main form of corrosion.
Common acid-base salt solution corrosion, atmospheric corrosion, soil corrosion, seawater corrosion, microbial corrosion, stainless steel pitting corrosion and crevice corrosion, etc. are all electrochemical corrosion.
Electrochemical corrosion not only occurs between two substances that can play a chemical role, but also due to the difference in concentration of the solution, the difference in the concentration of oxygen in the surroundings, the slight difference in the structure of the substance, etc. , The metal with low potential and the status of the positive plate is lost.
Nine anti-corrosion measures:
1. Electrochemical protection
There are two types of electrochemical protection: anode protection and cathode protection. If zinc is used to protect iron, zinc is corroded, and zinc is called sacrificial metal. In production practice, anode protection is used less and cathode protection is used more. Cast iron valve china and important valves use this cathode The protection method is an economical, simple and effective method. Adding zinc to the asbestos filler to protect the valve stem also belongs to the cathodic protection method.
2. Using non-metallic materials
Non-metallic corrosion resistance is excellent, as long as the valve temperature and pressure meet the requirements of non-metallic materials, not only can solve the problem of corrosion, but also save precious metals.
The valve body, bonnet, lining, sealing surface and other commonly used non-metallic materials are made. As for the gasket, the packing is mainly made of non-metallic materials.
The valve lining is made of plastics such as polytetrafluoroethylene, chlorinated polyether, and natural rubber, neoprene rubber, nitrile rubber, etc. The valve body and bonnet body are made of general cast iron and carbon steel. This ensures the strength of the valve and protects the valve from corrosion.
The pinch valve is also designed based on the excellent corrosion resistance and excellent variable performance of rubber. Now more and more pairs of plastics such as nylon, polytetrafluoroethylene, and natural rubber and synthetic rubber are used for various seals. Surface, sealing ring, used on various valves.

Aerodynamic Ball Valve
Aerodynamic Ball Valve

These non-metallic materials used as sealing surfaces have not only good corrosion resistance, but also good sealing performance, and are particularly suitable for use in media with particles. Of course, their strength and heat resistance are low, and the scope of application is limited.
The appearance of flexible graphite makes non-metals enter the high-temperature field, solves the problem of filler and gasket leakage that is difficult to solve for a long time, and is a good high-temperature lubricant.

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