Because of the special layout of the mechanical seal and the different working environment and conditions, the shapes of corrosion damage are also diverse. The common damage methods of mechanical seals such as PTFE seals and PTFE gaskets mainly include corrosion damage, thermal damage and mechanical damage. Among them, corrosion damage is more harmful.

Metal ring corrosion

1. The appearance is uniformly corroded. If the outer surface of the metal ring contacts the corrosive medium, and the metal itself is not resistant to corrosion, the outer surface will corrode. The phenomenon is leakage, early wear, damage, noise, etc. The uniform corrosion of the metal surface has two shapes: film-forming and non-filming. Metal corrosion without film is very risky. It is called stress corrosion cracking. The use of surfacing hard alloy and sealing rings such as cast iron, tungsten carbide, titanium carbide, etc., simply presents stress corrosion break. The corrosion process proceeds at a certain speed, which aggravates the galvanic corrosion.

2. Stress corrosion cracking. Metal has abrasion resistance under the simultaneous action of corrosion and tensile stress. The corrosion of the filled F4 ring mainly refers to the selective corrosion, dissolution or disintegration damage of the filling. For example, in hydrofluoric acid, the glass fiber molecules are thermally corroded. These cracks communicate with the entire sealing end face, accelerate the wear of the end face, and increase the leakage.

mechanical seal

Non-metallic ring corrosion

1. Corrosion of graphite ring. There are three reasons for its corrosion: First, when the end surface is overheated and the temperature is greater than 180 degrees, the impregnated resin must be broken away from the graphite ring to reduce the wear resistance of the ring; second, if the impregnated resin is improperly selected, the mechanical seal is cooled. The establishment of the system is mainly caused by the wrong selection of materials. Corrosion of the film, the passivation film usually has the characteristics of maintenance effect, but the materials used in the metal mechanical seal ring, such as stainless steel, cobalt, chromium alloy, etc. The passivation film on the outer surface is damaged by the end surface friction, and under the condition of lack of oxygen It is very difficult to form a new film. It is very necessary to select corrosion-resistant impregnating resin, select high-pressure impregnation, and increase the impregnation depth.

2. Oxidation of graphite ring. In an oxidizing medium, when the end face is dry or poorly cooled, a temperature of 350-40o ℃ can cause the graphite ring to react with oxygen, generate CO and gas, and make the end face rough or even break. The non-metallic ring will also break under the combined effect of chemical media and stress.

3. Corrosion of PTFE (tetrafluoroethylene gasket) sealing ring. Chemical changes will occur in the medium, and the wear resistance will also be reduced; third, the resin impregnation depth is not good, when the impregnated layer is worn away, the wear resistance will be reduced. When F4 is filled with glass fiber, cracks occur first in the thin area, and then develop in the depth, causing cracks. The mechanical seal ring cracks are usually radially divergent, but there can be one or more cracks. 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 disintegration damage of the filling. For example, in hydrofluoric acid, the glass fiber molecules are thermally corroded, so what to fill depends on the specific situation.

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