Corrosion types and protection methods of the hott

2022-08-11
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Corrosion types and protection methods of mechanical seals

Abstract: the corrosion technical damage of mechanical seals mainly includes: metal ring corrosion, non-metallic ring corrosion, auxiliary seal ring and its contact parts corrosion. For the corrosion damage of mechanical seals, the main protection methods include scientific material selection, structural design, maintenance and use

key words: mechanical seal; Corrosion; Protection method

mechanical seals are often damaged, and the common forms of damage mainly include corrosion damage, thermal damage and mechanical damage. Among them, corrosion damage is harmful. Due to the special structural form of mechanical seals and different working environment and conditions, the forms of corrosion damage are also diverse

l corrosion of mechanical seals

1.1 corrosion of metal rings

first, uniform corrosion on the surface. If the surface of the metal ring is in contact with corrosive media, and the metal itself is not resistant to corrosion, surface corrosion will occur, and its phenomena are leakage, early wear, damage, sound, etc. There are two forms of uniform corrosion on the metal surface, film-forming and film-free. The metal corrosion without film is very dangerous, and the corrosion process is carried out at a certain speed, which is mainly caused by the wrong material selection. For film-forming corrosion, the passive film usually has the characteristics of protection, but the passive film on the surface of the materials used for metal sealing rings, such as stainless steel, cobalt, chromium alloy, etc., is damaged in the end face friction, and it is difficult to form a new film under anoxic conditions, which intensifies galvanic corrosion

second, there are stress corrosion cracking of ball joints and ball seats during the stress period. Under the simultaneous action of corrosion and tensile stress, the metal first produces cracks in the weak area, and then develops in depth and produces cracks, which is called stress corrosion cracking. The static/contact experiment between rabbit cornea and lens was carried out with surfacing hard. 0. The results showed that the PMMA surface without plasmon treatment caused 10% to 30% cell damage, while the pmma/hema composite surface after record data processing only caused about 10% cell damage, However, the cell damage caused by pmma/nvp composite surface is less than 10%. Alloy and cast iron, tungsten carbide, imported mainly high-end wet diaphragm titanium carbide and other sealing rings are prone to stress corrosion cracking. Seal ring cracks are generally radial divergent, which can be one or more. These cracks connect the whole sealing face, accelerate the wear of the end face and increase the leakage

1.2 non metallic ring corrosion

first, graphite ring corrosion. There are three reasons for the corrosion of the impermeable graphite ring impregnated with resin: first, when the end face is overheated and the temperature is greater than 180oC, the impregnated resin should be folded away from the graphite ring, so that the wear resistance of the ring decreases; Second, if the impregnated resin is improperly selected, chemical changes will occur in the medium, which will also reduce the wear resistance; Third, the resin impregnation depth is not enough. When the impregnation layer is removed, the wear resistance decreases. Therefore, it is very necessary to select corrosion-resistant impregnating resin and adopt high-pressure impregnation to increase the impregnation depth for the establishment of sealed cooling system

second, oxidation of graphite ring. In oxidizing medium, when the end face is dry rubbed or poorly cooled, the temperature of 350 ~ 40o ℃ can make the graphite ring react with oxygen to produce CO and gas, which can make the end face rough or even crack. Non metallic rings will also break under the simultaneous action of chemical medium and stress

third, the corrosion of polytetrafluoroethylene (F4) sealing ring. F4 is filled with glass fiber, graphite powder, metal powder, etc. to improve its temperature resistance and wear resistance. The corrosion of the filled F4 ring mainly refers to the selective corrosion, dissolution or deterioration of the filling. For example, in hydrofluoric acid, glass fiber molecules are thermally corroded, so what to fill should depend on the specific situation

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