Nine Anti-Corrosion Measures of Valves (2)
Adopting the surface treatment for metals
Joints of valves
Galvanization, chromeplate and oxidation treatments can be adopted for bolts of valves so as to improve the bolts’ resistance to air and corrosive media. Besides the above mentioned three methods, the phosphorization surface treatment method can also be used for other fasteners according to the specific circumstances.
Sealing surfaces and closing elements with small larger diameters
Generally, nitridation, boronizing and other surface treatments can be used to increase the corrosion resistance and wear resistance of sealing surfaces and closing elements with small diameters.
Nitridation, boronizing, chromeplate, nickeling and other surface treatments can be utilized for improving corrosion resistance and abrasion resistance of valve stems.
Different surface treatments should be selected and used for valve stems made of different materials and under various working conditions. For the valve stem with the packing of asbestos, which will have the contact with the media such as air and water vapor, the hard chrome plating and gas nitriding treatments can be adopted. The ion nitriding treatment is unsuitable for stainless steel. If the valve stem is exposed to the air with the sulfuretted hydrogen, the electroplating high phosphor content nickel clad layer can be used to protect the valve stem from corrosion. The gas nitriding and ion nitriding treatments can be used for 38CrMoAlA material, while the hard chrome plating treatment can not be used. After hardening and tempering treatments, Cr13 material is resistant to ammonia. The carbon steel which has the gas nitriding treatment is also corrosion resistant. All the phosphor-nickel clad layers are not resistant to ammonia. The 38CrMoAlA material after the gas nitriding treatment has pretty excellent corrosion resistance and comprehensive performance, which makes it often used as raw materials of valve stems.
Valve bodies and hand wheels with small diameters
The chromeplate treatment is often adopted for valve bodies and hand wheels with small diamante to improve the anti-corrosion performance of valve bodies and hand wheels as well as to decorate valves.
Adopting the thermal spraying method
The thermal spraying is a kind of method for preparing coatings, which has become one of the new technologies for materials’ surface protection. Most metals and their alloys, metal oxide ceramics, metal cermet composites and hard metal compound can be coated by one or several thermal spraying methods.
The thermal spraying method can improve the surface’s corrosion resistance, wear resistance, high temperature resistance, etc. and extend the service life of the valve. The thermal spray special coating has the characteristics such as insulation, self-lubricating, heat radiation and electromagnetic shielding. Some parts can even be repaired through the thermal spray method.
Source: China Valves Manufacturer – Yaang Pipe Industry (www.ugsteelmill.com)