knowledge

Mechanical seal corrosion protection tips

First, metal ring corrosion

1, the surface is evenly 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 will occur. The phenomenon is leakage, early wear, damage, and sound. The metal surface is uniformly corroded in both film-forming and film-free shapes. The metal-free corrosion of the film is dangerous. It is called stress corrosion cracking. It is made of hardfacing alloy and cast iron, tungsten carbide, titanium carbide and other sealing rings. Split. The corrosion process proceeds at a certain speed, which increases the galvanic corrosion.


2, stress corrosion splitting. The metal mechanical seal of the metal under the action of corrosion and tensile stress, wear resistance. Corrosion filling the F4 ring mainly refers to selective corrosion, dissolution or enthalpy damage of the filling. For example, in hydrofluoric acid, the glass fiber molecules are thermally corroded, and these cracks communicate the entire sealing end face, which accelerates the wear of the end face and increases the leakage amount.


Second, non-metallic ring corrosion

1, graphite ring corrosion impregnated graphite ring impregnated with resin, its corrosion has three reasons: First, when the end face is overheated, the temperature is greater than 180 ° C, the impregnated resin should be folded off the graphite ring, so that the ring wear resistance is reduced; Second, if the impregnated resin is not properly selected, the seal cooling system is built to seal the plant, which is mainly composed of faults. The corrosion of the film formation, the passivation film generally has the 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 damaged in the end face friction, under the condition of anoxic new It is difficult to form a film. It is necessary to select a corrosion-resistant impregnating resin and use high-pressure impregnation to increase the impregnation depth.


2, the corrosion of the PTFE (tetrafluoroethylene gasket) sealing ring will be chemically changed in the medium, also reduce the wear resistance; third, the resin impregnation depth is not, when the impregnation layer is ground, the wear resistance is reduced .F4 is filled with glass fiber, firstly cracks occur in a thin zone, and then develop to the depth, splitting, the seal ring crack is generally radial divergence type, so one or more. 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 enthalpy damage of the filling. For example, in hydrofluoric acid, glass fiber molecules are thermally corroded, so what should be filled depends on the specific conditions.


3. Oxidation of the graphite ring. In an oxidizing medium, when the end faces are dry or poorly cooled, a temperature of 350 to 40 ° C can cause the graphite ring to react with oxygen, and CO and gas can be generated to roughen or even split the end faces. Non-metallic rings also split under the action of chemical media and stress.