**Abstract:**
Corrosion damage in mechanical seals is a common issue that can significantly affect their performance and lifespan. It typically manifests in several forms, including corrosion of metal rings, non-metallic rings, and auxiliary seals, as well as the contact areas between these components. To mitigate such damage, it's essential to focus on material selection, structural design, and proper maintenance during operation. Understanding the different types of corrosion and their causes is crucial for implementing effective protective measures.
**Keywords:** mechanical seal; corrosion; protection methods
Mechanical seals are frequently subjected to various types of damage, with corrosion being one of the most severe. Other common damages include thermal and mechanical wear. Among these, corrosion damage poses a greater threat due to its potential to compromise the integrity of the sealing system over time. The unique structure and operating conditions of mechanical seals contribute to diverse forms of corrosion, making it a complex issue to address.
**1. Corrosion in Mechanical Seals**
**1.1 Corrosion of Metal Rings**
The first type of corrosion involves uniform surface degradation. When the metal ring comes into contact with corrosive media and the material lacks sufficient resistance, surface corrosion occurs. This can lead to leakage, premature wear, or even failure. Uniform corrosion may occur either with or without a protective film. However, when no film is present, the corrosion process is more dangerous, often caused by improper material selection. In cases where a passivation film is formed, materials like stainless steel, cobalt alloys, or chrome alloys are commonly used. However, during end-face friction, this protective layer can be damaged, especially in oxygen-deficient environments, leading to increased galvanic corrosion.
Another form of corrosion is stress corrosion cracking. This occurs when a metal is exposed to both a corrosive environment and tensile stress. Cracks tend to initiate at weak points and propagate deeper, eventually causing fracture. Materials such as hardfacing alloys, cast iron, tungsten carbide, and titanium carbide are particularly susceptible to this type of damage. Cracks in the seal ring usually radiate outward and can occur in multiple locations. These cracks can connect across the entire sealing face, accelerating wear and increasing the likelihood of leakage.
**1.2 Corrosion of Non-Metallic Rings**
One common issue is the corrosion of graphite rings. Impervious graphite rings impregnated with resin are vulnerable to three main causes of degradation: excessive heat at the end face (over 180°C), which can cause the resin to separate from the graphite and reduce wear resistance; chemical reactions due to incorrect medium selection; and insufficient impregnation depth, which reduces the ring’s durability. To prevent this, it's important to implement an efficient cooling system, choose corrosion-resistant resins, and use high-pressure impregnation techniques to ensure deep penetration.
Oxidation is another concern for graphite rings. In oxidizing environments, if the end face becomes dry or poorly cooled, temperatures between 350–400°C can trigger a reaction between the graphite and oxygen, producing carbon monoxide and gas. This can lead to surface roughening or even fracture. Similarly, non-metallic rings can also crack under the influence of chemical media and mechanical stress.
Additionally, polytetrafluoroethylene (PTFE) seal rings, often reinforced with glass fiber, graphite, or metal powders, can suffer from selective corrosion of the fillers. For example, in hydrofluoric acid, the glass fibers may degrade thermally. Therefore, the choice of filler material should be tailored to the specific working environment to ensure optimal performance and longevity.
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