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Mechanical seals often suffer damage, with the common forms of damage including corrosion damage, thermal damage, and mechanical damage. Among them, corrosion damage is particularly harmful. Due to the special structural design of mechanical seals as well as varying working environments and conditions, the forms of corrosion damage are diverse. I. Corrosion of metal rings 1. Uniform surface corrosion: If the surface of a metal ring comes into contact with corrosive substances and the metal itself is not resistant to corrosion, surface corrosion will occur. The symptoms of this include leakage, premature wear, damage, and noise generation. Uniform corrosion on metal surfaces occurs in two forms: film-forming and film-free. Film-free metal corrosion is very dangerous, and the corrosion process proceeds at a certain rate; this is mainly caused by incorrect material selection. In film-forming corrosion, the passive film typically exhibits protective properties. However, for materials used in metal seal rings—such as stainless steel, cobalt, and chromium alloys—the passive film on their surfaces gets damaged during end-face friction. Under oxygen-deficient conditions, it is difficult for a new film to form, thereby exacerbating galvanic corrosion. 2. Stress corrosion cracking: When a metal is subjected to both corrosion and tensile stress, cracks first appear in the weak areas, and these cracks then propagate deeper, leading to failure. This phenomenon is known as stress corrosion cracking. The use of wear-resistant alloys, cast iron, tungsten carbide, titanium carbide, and other types of sealing rings can increase the likelihood of stress corrosion cracking. Seal ring cracks are generally radially diverging and can be one or multiple. These cracks connect the entire sealed end face, accelerating its wear and increasing the leakage rate. II. Corrosion of non-metallic rings 1. Corrosion of graphite rings: Impermeable graphite rings impregnated with resin suffer from corrosion for three reasons: (1) When the end face becomes overheated, with a temperature above 180°C, the resin impregnated in the ring separates from it, reducing the ring’s wear resistance. (2) If the resin used for impregnation is not chosen properly, chemical changes will occur in the medium, which also reduces wear resistance. (3) The resin impregnation depth is insufficient; once the impregnated layer is worn away, the wear resistance decreases. Therefore, it is essential to establish a sealed cooling system, select corrosion-resistant impregnation resins, use high-pressure impregnation, and increase the impregnation depth. 2. Oxidation of graphite rings: In oxidative media, when there is dry friction at the end faces or poor cooling, temperatures of 350–400°C can cause the graphite rings to react with oxygen, producing CO gas. This can result in roughening of the end faces or even their rupture. Non-metallic rings can also break under the combined effect of chemical media and stress. 3. Corrosion of polytetrafluoroethylene (F4) sealing rings: F4 is reinforced with materials such as glass fiber, graphite powder, and metal powder to improve its heat resistance and wear resistance. The corrosion of the F4 ring filler mainly refers to the selective corrosion, dissolution, or degradation damage of the filler. For example, in hydrofluoric acid, glass fiber molecules undergo thermal corrosion; therefore, what to use as a filler depends on the specific circumstances.