Corrosion of mechanical seal 

A Corrosion metal ring 
a. The surface uniform corrosion.If contact surface of the metal ring corrosive medium, and the metal itself is not corrosion resistance, can produce a surface corrosion, the phenomenon of leakage, early wear and tear, damage, etc.Uniform corrosion on metal surface has membrane and membrane two forms, no film of metal corrosion is very dangerous, corrosion process to a certain speed, this mainly due to material errors.Film-forming corrosion, the characteristics of the passivation film usually has a protective effect, but the metal seal ring used in materials, such as stainless steel, cobalt, chromium alloy, such as the surface passivation membrane damage in the end surface friction, under the condition of oxygen new membrane is difficult to generate, exacerbated galvanic corrosion. 
b. Stress corrosion cracking.Metal under the effect of corrosion and the tensile stress at the same time, the first cracks in the weak area, thus to further development, produce rupture, known as stress corrosion cracking, selects the built-up welding hard alloy and cast iron sealing ring, tungsten carbide, titanium carbide, prone to stress corrosion cracking.Sealing ring radial cracks are generally divergent, can be one or more.These cracks communication throughout the seal face, accelerated the end face of wear, increase the leakage. 

B Non-metallic corrosion ring 
a. The graphite ring corrosion.Not impregnated with resin permeability graphite ring, its corrosion for three reasons: 
1) When the end face overheating, the temperature greater than 180 oc, impregnated resin to fold from graphite ring, ring wear resistance decreased; 
2) Improper choice impregnation of resin, chemical changes in the media, also decrease abrasion resistance; 
3) Resin impregnation of depth, after grinding to dipping layer, wear resistance.So sealed cooling system, choose the impregnating resin corrosion resistant, adopts high pressure impregnation, increase the immersion depth is very necessary. 
b. The oxidation of graphite ring.In oxidizing medium, face in dry friction or cooling, it produces 350 ~ 400 ? temperature can make the graphite rings react with oxygen, CO gas, can make the end face rough and even rupture.Non-metallic ring in the chemical medium and stress at the same time, under the action of will burst. 
c. PTFE corrosion of seal ring.F4 filler such as glass fiber, graphite powder, metal powder to improve its temperature resistance, wear resistance.Fill the F4 ring corrosion is mainly refers to fill the selective corrosion, dissolution, or metamorphic damage.In hydrofluoric acid, for example, the glass fiber molecular hot corrosion of mechanical seal, so fill what should depending on the specific situation. 

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