Detailed explanation of common sense of corrosion protection of mechanical seals

Detailed explanation of common sense of corrosion protection of mechanical seals

Due to the special planning methods of mechanical seals and different working environments and conditions, the shapes of mechanical seals damaged by corrosion are also varied. The common damage methods of mechanical seals such as PTFE sealing rings and PTFE gaskets mainly include corrosion damage, thermal damage and mechanical damage. During the corrosion damage is more dangerous. 1. Corrosion of the metal ring 1, the surface is uniformly corroded. If the surface of the metal ring touches the mechanical seal and the corrosive medium, and the metal itself is not resistant to corrosion, surface corrosion will occur, and the phenomenon is leakage, early wear, damage, and sound. The uniform corrosion of the metal surface has two forms: film-forming and film-free. The metal without film is very dangerous to corrode, which is called stress corrosion cracking. The use of surfacing cemented carbide and sealing rings such as cast iron, tungsten carbide, and titanium carbide can easily cause stress corrosion. split. The corrosion process proceeds at a certain speed, which aggravates the galvanic corrosion. 2. Stress corrosion cracking. Metal cartridge mechanical seal under the combined effect of corrosion and tensile stress, 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, the glass fiber molecules are thermally corroded, and these cracks communicate with all the sealing end faces, and the wear of the end face is added immediately, which increases the leakage. 2. Non-metallic ring corrosion 1. Graphite ring corrosion. There are three reasons for the corrosion of the impermeable graphite ring impregnated with resin: one is that when the end face is overheated and the temperature is greater than 180oC, the impregnated resin must be broken away from the graphite ring to reduce the wear resistance of the ring; The selection is not appropriate, so the establishment of a sealing parts factory for the sealing cooling system is mainly caused by the faulty selection of materials. For film-forming corrosion, the passivation film usually has the characteristics of protective effect, but the materials used for metal sealing rings, such as stainless steel, cobalt, chromium alloy, etc., are damaged in the end face friction The film is difficult to form. It is very necessary to choose a corrosion-resistant impregnating resin, use high-pressure impregnation, and increase the impregnation depth. 2. Corrosion of PTFE (tetrafluoroethylene gasket) sealing ring. Chemical changes will occur in the medium, which will also reduce the wear resistance; the third is that the depth of resin impregnation is not enough. When the impregnated layer is removed, the wear resistance will be reduced. Filled with F4 such as glass fiber, cracks first occur in the thin area, and then develop to the depth and split. The cracks of the sealing ring are usually radially divergent, and there may 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 deterioration of the filling. For example, in hydrofluoric acid, the glass fiber molecules are thermally corroded, so what is filled should be determined according to the specific situation. 3. Oxidation of graphite rings. In an oxidizing medium, when the end face is in dry contact or poorly cooled, the temperature of 350 to 40°C can cause the graphite ring to react with oxygen, generate CO, and gas, which can make the end face rough and even split. Non-metallic rings will also split under the combined effect of chemical media and stress.