Abstract: The corrosion damage of mechanical seals mainly includes: metal ring corrosion, non-metallic ring corrosion, corrosion of auxiliary seals and their contact parts. For the mechanical seal corrosion damage, the main protection methods are scientific material selection, structural design, maintenance and use.
Key words: mechanical seal; corrosion; protection method
Mechanical seals are often damaged. Common forms of damage are corrosion damage, thermal damage and mechanical damage. Corrosion damage is more harmful. Due to the special structural form and working environment and conditions of mechanical seals, the forms of corrosion damage are also various.
l Mechanical seal corrosion
1.1 Metal ring corrosion
First, the surface is uniformly corroded. If the surface of the metal ring is in contact with the corrosive medium, and the metal itself is not resistant to corrosion, surface corrosion occurs, which is leakage, early wear, damage, sound, and the like. The metal surface is uniformly corroded in both film-forming and film-free forms. The metal-free corrosion of the film is dangerous, and the corrosion process is carried out at a certain speed, which is mainly caused by the material selection error. In the film formation, the passivation film usually has a protective property, but the material used for the metal sealing ring, such as stainless steel, cobalt, chrome alloy, etc., the surface of the passivation film is destroyed in the end face friction, under the condition of anoxic The membrane is difficult to form, which increases galvanic corrosion.
Second, stress corrosion cracks. Under the action of corrosion and tensile stress, the metal firstly produces cracks in the weak area, and then develops into the depth, causing cracking, called stress corrosion cracking. The hardfacing alloy and the sealing ring such as cast iron, tungsten carbide and titanium carbide are used. Stress corrosion cracking is prone to occur. The seal ring cracks are generally radially divergent and may be one or more. These cracks communicate the entire sealing end face, accelerating the wear of the end face and increasing the amount of leakage.
1.2 Non-metallic ring corrosion
First, the graphite ring is corroded. Impervious graphite ring impregnated with resin, its corrosion has three reasons: First, when the end face is overheated, when the temperature is greater than 180oC, the impregnated resin should be folded away from the graphite ring to reduce the wear resistance of the ring; If it is not properly selected, it will cause chemical changes in the medium and also reduce the wear resistance. Third, the resin is not deeply impregnated. When the impregnation layer is removed, the wear resistance is reduced. Therefore, the establishment of the sealed cooling system, the choice of corrosion-resistant impregnating resin, the use of high-pressure impregnation, it is necessary to increase the impregnation depth.
Second, the oxidation of the graphite ring. In an oxidizing medium, when the end face is dry or poorly cooled, a temperature of 350 to 40 ° C is generated to cause the graphite ring to react with oxygen to generate CO and gas, which may cause the end face to be roughened or even broken. Non-metallic rings also rupture under the action of chemical medium and stress.
Third, the corrosion of the polytetrafluoroethylene (F4) seal ring. F4 is filled with glass fiber, graphite powder, metal powder, etc. to improve its temperature resistance and wear resistance. Corrosion filling the F4 ring mainly refers to selective corrosion, dissolution or deterioration of the filling. For example, in hydrofluoric acid, glass fiber molecules are thermally corroded, so what should be filled depends on the specific situation.
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