Corrosion of a valve is generally understood to be the damage of a valve metal material under the action of a chemical or electrochemical environment. Since the "corrosion" phenomenon occurs in the spontaneous interaction between the metal and the surrounding environment, how to isolate the metal from the surrounding environment or use more non-metallic synthetic materials has become a common concern.
It is well known that corrosion damage of metals has a considerable influence on the duration of action, reliability and service life of the valve. The action of mechanical and corrosive factors on the metal greatly increases the total amount of wear on the contact surface. The total amount of wear on the surface of the friction during operation of the valve. During operation of the valve, the frictional surface is subject to wear and damage 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 complex; the presence of hydrogen sulfide, carbon dioxide and some organic acids in media such as oil, natural gas and oil layer water increases the destructive force of the metal surface and thus quickly loses working ability.
The chemical corrosion of metals depends on the temperature, the mechanical load of the friction parts, the stability of the sulfides and their acid resistance contained in the lubricant, the duration of contact with the medium and the catalysis of the metal on the nitriding process, corrosion and corrosion. The rate at which a molecule's molecules switch to metal, and so on. Therefore, the anti-corrosion method (or measure) of metal valves and the application of synthetic material valves have become one of the themes of current valve industry research.
1. The anti-corrosion of metal valves can be understood as the protection of the metal valve on the protective layer (such as paint, pigment, lubricating material, etc.) to protect it from corrosion, so that the valve is manufactured, stored, transported or in its Not subject to corrosion during all processes used
The method of corrosion protection of metal valves is determined by the required protection period, transportation and storage conditions, valve construction characteristics and materials, and of course, the economic effects of anti-corrosion are considered.
There are four main methods for preserving metal valves and their components:
The volatile corrosion inhibitor is placed in the atmosphere of the steam (wrapped with resist paper, blown to inhibit air from passing through the product chamber, etc.).
Use blocked water and alcohol solutions
Apply a thin layer of anti-corrosion (protective) material to the surface of the valve and its components.
A thin layer of film or polymer that is resisted is applied to the valve and its components.
(Note: At present, valve manufacturers widely use lubricating materials and water resistance to dissolve the liquid to prevent corrosion.)
Second, the application of material valves
Synthetic valves are superior to metal valves in many corrosive conditions, first of all corrosion resistance, followed by net weight, and their strength depends on the shape, arrangement and number of reinforcing fibers. (In general, the greater the percentage of fiber, the greater the strength of the synthetic material.) In valve applications, the weight content of the fiber is generally in the range of 30% to 40%, and its chemical stability is mainly immersed in the final product of Zui. The resin body properties of the sealing fiber are determined. In synthetic valve, the solid polymer body can be either thermoplastic (such as PVC-polyvinylidene fluoride, PPS-polyphenylene sulfide, etc.) or thermosetting resin (such as polyester, ethylene and epoxy resin). Wait). The thermosetting resin retains its strength at a dielectric temperature better than a thermoplastic (ie, the thermosetting resin has a higher heat distortion temperature). (Note: In the operating conditions, the measurement of the heat resistance of the synthetic material is called the heat distortion temperature.
At present, the synthetic material commonly used in chemical process valves is vinyl epoxy (thermoplastic material), and the reinforcing fibers are chopped glass fiber (1/4 inch long) and chopped graphite fiber (1/4 inch long). ). The table below compares the performance of synthetic materials widely used by Zui with the properties of corrosion resistant metals. From the surface analysis, the glass and graphite reinforced composite materials have lower tensile strength than metals. Therefore, the parts with large stress on the synthetic material valve should have a thicker section and be reinforced with the same ribs to achieve the same metal. performance.
Due to the corrosion resistance, high strength and light weight of synthetic material valves, it is an economical alternative valve product in the corrosive conditions of many metal or glass fiber reinforced plastic piping systems. Synthetic material valves have excellent prospects for use in chemical process conditions.
In the valve industry, the use of organic and synthetic materials is no longer the concept of traditional metal and non-metallic valve materials. Ceramic (can increase the operating temperature of the valve from 400 ° C to over 1200 ° C), plastic (with rust and corrosion resistance), synthetic materials (with corrosion resistance, light weight, high strength), memory alloy (using shape Valves made of memory alloys or temperature memory alloys with reversibility and high elasticity). New materials are developing a large number of new valves with high performance. The development of new technologies has made it possible to apply various engineering materials to the valve manufacturing industry.
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