Mechanical Seal Failure Causes and Prevention

Mechanical seals are among the most reliability-critical components in fluid machinery. Their failure directly causes media leakage, equipment downtime and even environmental incidents. According to Huahao Sealing Co., Ltd.'s after-sales statistics, more than 60% of unplanned centrifugal pump shutdowns relate to mechanical seal failure. Based on field service cases, this article systematically analyzes the main failure modes, root causes and preventive measures for mechanical seals.

1. Face Wear Failure

Face wear is the most common failure form, accounting for about 45% of total cases.

1.1 Normal vs. Abnormal Wear

Mechanical seal faces wear slowly during normal operation. Annual wear below 0.05mm is normal. When wear rate significantly exceeds this, abnormal wear is indicated. Diagnosis methods include periodic measurement of seal ring height, monitoring leak rate trends and tracking face temperature changes.

1.2 Causes of Abrasive Wear

Solid particles in the medium are the leading cause of abrasive wear. Even particles smaller than 5μm cause three-body wear in the face film. Preventive measures include inlet filters, flush liquid schemes and harder mating materials such as silicon carbide.

1.3 Dry Friction Face Burns

Dry friction is another severe face failure mode, often occurring at pump start-up without venting, flush interruption or media vaporization. Under dry friction, face temperature can rise above 300°C within seconds, causing carbon graphite face oxidation, resin impregnant decomposition and seal face burns. Prevention centers on ensuring proper flush operation and full venting before start-up.

2. Secondary Seal Failure

Secondary seals (O-rings, V-rings, etc.) do not perform the primary sealing function, but their failure causes overall seal failure nonetheless.

2.1 Aging and Deformation

Rubber seals age, harden and develop compression set under long-term high temperature and media exposure. Fluorocarbon has a long-term upper limit of 200°C, nitrile 120°C; exceeding these temperatures causes rapid aging. Material should be selected based on medium temperature, with replacement every 2-3 years.

2.2 Chemical Corrosion

Some media selectively attack rubber. Benzene solvents cause nitrile swelling; strong oxidizers damage fluorocarbon molecular chains. The key prevention is to verify media-seal material chemical compatibility.

2.3 Installation Damage

Using sharp tools during installation, surface burrs or insufficient lubrication can all damage seals. Huahao recommends using dedicated tools with silicone oil or dedicated lubricants during installation.

3. Spring and Bellows Failure

Springs and bellows are the compensating elements of mechanical seals; their failure leads to insufficient face pressure and seal failure.

3.1 Spring Fatigue Fracture

Springs suffer fatigue fracture under long-term cyclic loads, especially in frequent start-stop conditions. Prevention includes selecting spring materials with higher fatigue life and avoiding frequent starts and stops.

3.2 Spring Corrosion

Media corrosion reduces spring cross-sectional area and stiffness, ultimately losing compensation ability. For highly corrosive service, use Hastelloy, Monel or other corrosion-resistant spring materials, or switch to external mechanical seal structures.

3.3 Bellows Cracking

Metal bellows can crack under combined fatigue and corrosion. Periodic visual inspection is recommended, focusing on cracks at the crest and root of bellows waves.

4. Corrosion Failure

Carbon graphite seal rings themselves have good corrosion resistance, but their associated metal parts (spring seats, drive pins, push rings) are prone to corrosion failure.

4.1 Galvanic Corrosion

Different metals form galvanic cells in electrolytic media; the more anodic metal corrodes faster. For example, a stainless steel spring seat and carbon steel pump shaft will form a galvanic couple in chloride media. Prevention includes using the same material, adding insulating gaskets or applying cathodic protection.

4.2 Crevice Corrosion

In assembly crevices of seal parts, media stagnation forms a localized corrosive environment. In chloride media, the crevice corrosion critical temperature of 316 stainless steel is only about 60°C. Assembly structures should be optimized to minimize crevices.

4.3 Stress Corrosion Cracking

Austenitic stainless steels undergo stress corrosion cracking under combined chloride media and tensile stress. Prevention includes reducing residual stress and using duplex stainless steels or high-nickel alloys.

5. Integrated Prevention Strategy

Building a mechanical seal reliability management system is the fundamental path to failure prevention. Huahao recommends the following measures: establish a seal component ledger recording model, installation time and operating conditions; conduct periodic inspection of leak rate, vibration and temperature; set preventive replacement intervals based on conditions; build failure analysis archives for continuous selection improvement.

6. Conclusion

Mechanical seal failure causes are complex, often involving media, conditions, installation and maintenance. Systematic failure mode analysis combined with preventive maintenance can significantly reduce failure frequency. Huahao Sealing Co., Ltd. offers seal failure analysis services. Welcome to contact us for cooperation.