Corrosion of metal valves and the application of synthetic valves The corrosion of valves is commonly understood as the destruction of valve metal materials under the effects of chemical or electrochemical environments. As "corrosion" occurs in the spontaneous interaction between metal and the surrounding environment, how to separate metals from the surrounding environment or use more non-metallic synthetic materials has become a common concern. As we all know, metal corrosion damage to the valve's duration, reliability and service life have a considerable impact. The effect of mechanical and corrosion factors on the metal greatly increases the total amount of contact surface wear. Valve in operation, the total amount of wear on the surface of the friction. During operation of the valve, the frictional surface is subject to wear and tear as a result of simultaneous mechanical action and chemical or electrochemical interaction of the metal with the environment. For valves, the climatic conditions of the pipeline work are complicated; the presence of hydrogen sulfide, carbon dioxide and certain organic acids in media such as oil, natural gas and formation water increases the destructive power of their metal surfaces and rapidly loses their ability to work. As the metal's chemical corrosion depends on the temperature, the mechanical load on the friction parts, the sulfide contained in the lubricating material and its acid resistance, the duration of the contact with the medium and the catalytic effect of the metal on the nitriding process, Material molecules on the metal conversion speed and so on. Therefore, the anticorrosion method (or measure) of metal valve and the application of synthetic material valve have become one of the topics of the valve industry research at present. 1. Anticorrosion of metal valves is to be understood as applying a protective coating (such as paint, pigments, lubricants, etc.) on metal valves that protects them against corrosion so that the valve, whether manufactured, stored, transported or in its The entire process is not subject to corrosion. The method of metal valve corrosion protection depends on the required protection period, shipping and storage conditions, valve construction features and materials, and of course, the economic effects of antisepsis to be considered. There are four main methods of anticorrosive metal valves and their parts: 1, the volatile anti-corrosion agent into the atmosphere of the steam (wrapped with a resistive paper, blowing air to inhibit the passage of products through the chamber, etc.). 2, using the resistance of water and alcohol solution. 3, the anti-corrosion (protection) material coated on the valve and its parts surface. 4, the resistance of the thin film or polymer coating on the valve and its parts surface. (Note: The current valve manufacturers, the widespread use of lubricants and water resistance to dissolve the flow of anti-corrosion. Second, the application of materials and valves Synthetic valves, in many corrosive conditions are better than the metal valve, the first is corrosion resistance , Followed by the net weight, and its strength depends on the shape, arrangement and amount of reinforcing fibers (generally, the greater the percentage of fibers, the greater the strength of the composite.) In valve applications, the weight content of the fibers In the range of 30% -40%, and its chemical stability is mainly determined by the properties of the resin encapsulating the fiber in the final product. In synthetic valves, the solid polymer body may be either a thermoplastic (eg PVC-poly Vinyl fluoride, PPS-polyphenylene sulfide, etc.) or thermosetting resins (such as polyester, ethylene, epoxy, etc.) Thermosetting resins are superior to thermoplastics in maintaining their strength at a temperature Thermosetting resins have a higher heat deflection temperature.) (Note: The determination of the thermal resistance of a composite during its service life is referred to as the heat distortion temperature.) Currently, The most commonly used synthetic material for chemical process valves is vinyl epoxies (thermoplastics) reinforced with shredded glass fibers (1/4 inch long) and shredded graphite fibers (1/4 inch long). the table below with the performance properties of corrosion-resistant metal composite materials most widely used as a comparison. graphite reinforced glass-reinforced vinyl-vinyl graphite reinforced PPS 316SS Hast-C tensile strength (Psi) Bending Strength (Psi) NA NA Compressive Strength (Psi) Heat Deflection Temperature (° F) NA NA Coefficient of Thermal Expansion (in / in / ° F) 15 × 10-6 15 × 10 -6 13 × 10-6 6.3 × 10-6 9.9 × 10-6 Note: NA is not applicable (or invalid) From the surface analysis, glass and graphite reinforced composite materials compared to metal, its tensile strength is lower Therefore, the valve of synthetic material should have a thicker cross-section and with ribs to achieve the same performance as the metal, due to the corrosion resistance, high strength and light weight of the composite valve, a lot of Metal or fiberglass reinforced plastic piping systems, corrosive conditions, more economical optional valve products in the chemical process conditions, excellent prospects for the use of synthetic valves in the valve industry, the use of organic materials and synthetic materials , Is not the traditional concept of metal and non-metallic valve materials.Ceramics (the valve temperature can be increased from 400 ℃ to 1200 ℃ above), plastic (with anti-corrosion characteristics), synthetic materials (with corrosion resistance, Light weight and high strength), memory alloy (valve made of reversible shape and high elasticity of shape memory alloy or temperature memory alloy), and the like. New materials, is developing a large number of high-performance valve with new products. The development of new technologies, so that a variety of engineering materials used in valve manufacturing has become possible.
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