fluorine lining gate valve

How to maintain the anti-corrosion valve daily

by:Lianke Valve     2022-06-26
How to maintain the anti-corrosion valve daily? Corrosion is the destruction and deterioration of materials under the action of various environments. The corrosion of metals is mainly caused by chemical corrosion and electrochemical corrosion, and the corrosion of non-metallic materials is generally caused by direct chemical and physical damage. Corrosion is one of the important factors that cause valve damage. Therefore, in the use of valves, corrosion protection is the first issue to be considered. Forms of valve corrosion: There are two forms of corrosion of metal valves, namely uniform corrosion and localized corrosion. (1) Uniform corrosion Uniform corrosion occurs on the entire surface of the metal. Such as stainless steel, aluminum, titanium, etc., a protective film produced in an oxidizing environment, and the metal under the film is uniformly corroded. There is also a phenomenon that the corrosion film on the metal surface peels off, and this corrosion is the most dangerous. (2) Localized corrosion Localized corrosion occurs at the local location of the metal, and its forms include pitting corrosion, crevice corrosion, intergranular corrosion, stress corrosion, fatigue corrosion, selective corrosion, wear corrosion, cavitation corrosion, friction corrosion, Hydrogen etch, etc. ① Pitting corrosion usually occurs on the passivation film or protective film metal. It is due to the existence of defects on the metal surface and the active ions of the self-destructing passivation film in the solution, which partially destroys the passivation film and protrudes into the metal to become corrosion holes. It is one of the most destructive and hidden corrosion forms in metals. ② Crevice corrosion occurs in environments such as welding, riveting, gaskets or under deposits. It is a special form of pitting corrosion. The method of prevention is to eliminate crevices. ③ Intergranular corrosion is a process that penetrates deep into the metal along the grain boundary from the surface, so that the grain boundary is corroded in the form of a network. In addition to the deposition of impurities at the grain boundary, the intergranular corrosion is mainly caused by improper heat treatment and cold working. Both sides of the weld of austenitic stainless steel are prone to corrosion due to chromium-poor areas. Intergranular corrosion of austenitic stainless steels is the most common and most dangerous form of corrosion. The methods to prevent intergranular corrosion of austenitic stainless steel valve parts are as follows: solution quenching treatment, that is, heating to about 1100t water quenching, selecting austenitic stainless steel containing titanium and niobium and carbon content below 0.03% to reduce Production of chromium carbide. ④ Delamination corrosion occurs in the layered structure. The corrosion develops vertically and inwardly first, and then corrodes the material with the parallel surface. Under the expansion force of the corrosive material, the surface layer is exfoliated. ⑤ Stress corrosion occurs in the cracks caused by the simultaneous action of corrosion and tensile stress. Methods to prevent stress corrosion: Eliminate or reduce the stress generated in welding and cold working by heat treatment; improve unreasonable valve structure, avoid stress concentration, use electrochemical protection, spray anti-corrosion coating, add erosive agent, apply compressive stress, etc. measure. ⑥ Corrosion fatigue occurs in the joint action of alternating stress corrosion, which causes the metal to crack. Heat treatment can be carried out to eliminate or reduce stress, surface shot peening and electro-galvanizing, chromium, nickel, etc., but it should be noted that the coating should not have tensile stress and hydrogen diffusion. ⑦ Selective corrosion occurs in materials with different compositions and impurities. In a certain environment, some elements are corroded and leached, and the remaining uncorroded elements are sponge-like. Common ones include dezincification of brass, dealumination of copper alloys, and graphitization of cast iron. ⑧ Wear corrosion is a form of corrosion caused by the alternating action of fluid on metal wear and corrosion. It is a common corrosion of valves. This corrosion occurs mostly on the sealing surface. The prevention method is to choose corrosion-resistant and wear-resistant materials, improve the structural design, and use cathodic protection. ⑨ Cavitation corrosion, also known as cavitation and cavitation, is a special form of wear corrosion. It is the bubbles generated in the fluid, the shock wave generated when the brick is extinguished, the pressure can be as high as 4ooatm (1atm u003d 101325Pa), the metal protective film is damaged, and even the metal particles are torn apart, and then corroded to form a film. This process is repeated continuously. Corrode metals. To prevent cavitation corrosion, cavitation-resistant corrosion-resistant materials can be selected, and the processed muscle elastic protective layer and cathodic protection with high surface roughness precision can be selected. ⑩ Frictional corrosion is the damage of the contact surface caused by vibration and sliding when two parts in contact with each other bear the load at the same time. Frictional corrosion occurs at the bolt connection, the connection between the valve stem and the closing part, between the ball bearing and the shaft, etc. It can be protected by lubricating grease, reducing friction, surface phosphating, selecting cemented carbide, and improving surface hardness by shot peening or cold working.
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