Why Do Silicon Carbide Mechanical Seals Fail? 5 Common Causes and Solutions

Silicon carbide possesses high wear resistance, corrosion resistance, and high-temperature resistance. It is widely used in face seals for petrochemical, metallurgical, pump, and valve applications. Silicon carbide mechanical seals a critical line of defense to ensure the continuous and stable operation of equipment.

In practical applications, many factories face issues of seal failure. It not only increases operation and maintenance costs, but also poses safety risks of leakage and downtime. This article focuses on 5 common failures and causes of silicon carbide mechanical seals and provides improvement solutions to help industrial O&M teams efficiently resolve sealing challenges.

Leakage

Leakage is the most common issue for silicon carbide mechanical seals. It leads to media seepage and may cause safety accidents.

There are 5 main causes of leakage. For ease of display in this part, the left column represents the causes, and the right column represents the solutions.

Friction and Wear Failure

Friction and wear are two main reasons for degradation and reduced life in silicon carbide mechanical seals.

Causes

When exposed to high-speed working conditions, friction between the faces of mechanical seals will eventually cause surface wear or scratching, reducing sealing effectiveness.

When the seal chamber lacks media liquid, the friction pair undergoes dry friction. In such a condition, the SiC rotating ring experiences severe wear, while the stationary ring is prone to thermal cracking.

In addition, solid particles in the media will impact the seal faces continuously. This wear is significantly intensified in particulate media.

Solutions

For low-power equipment, a combination of silicon carbide ceramic and graphite can be used to reduce friction and wear.

If silicon carbide is necessary, you may use components produced by pressureless sintering or reaction sintering.

Moreover, ensure sufficient media in the seal chamber to avoid dry friction. You can use lubrication monitoring devices to add media on time.

In solid particle working conditions, you can add sand guard rings to intercept impurities. You can also optimize the sealing face lubrication system by utilizing water lubrication or solid lubrication. It helps form a low-shear-strength lubricating film, keeping the friction coefficient within an acceptable range.

Overheating and Corrosion Failure

Overheating and corrosion always act together to accelerate the failure of SiC mechanical seals.

Causes

Most overheating stems from incorrect lubrication and sealing materials, or the inability to dissipate heat generated by friction on time. It also accelerates the aging of O-rings, compromising the sealing structure.

Corrosive media such as strong acids, strong alkalis, and organic solvents will erode silicon carbide sealing parts. In a strong oxidizing environment, the corrosion increases significantly if using insufficient-purity SiC.

Moreover, in an insufficient oxygen environment, SiC is oxidized to yield loose SiO powder rather than SiO2 film. It will make corrosive wear worse.

Solutions

For overheating, optimize your cooling system. Depending on the heat load, natural cooling, internal circulation cooling, or external flush cooling should be used to control the temperature of the seal. Flush cooling can also prevent impurities from accumulating.

Select appropriate SiC materials based on the corrosiveness of the media. For strong oxidizing media, pressureless sintered or hot-pressed silicon carbide is preferred. In corrosive conditions, use coatings on the surface of seal rings to strengthen their anti-corrosion capabilities. Don’t forget to inspect the composition of the media and replace degraded media in time.

Friction Pair Seizure

This failure is usually experienced in machines with low powers and low starting torques, like centrifugal pumps. The seizure of sealing parts makes it impossible for the machines to start.

Causes

The main reason is improper pairing of friction pair materials. For example, when using a seal combination of graphite and silicon carbide, the stationary SiC ring may adhere to the graphite, creating seizure resistance.

A mismatch between seal selection and equipment power or operating conditions can also lead to frequent seizure failures.

Solutions

Select appropriate sealing components strictly according to equipment power and operating conditions. For friction pair material pairing, prioritize pairs with complementary material characteristics.

Moreover, continuous maintenance of silicon carbide mechanical seals is required. Clean the friction pairs regularly to remove adhered graphite or impurities.

Check the friction pair before starting the equipment. If there is a seizure, disassemble and clean it to avoid equipment damage from forced starting.

Seal Damage and Improper Installation

Silicon carbide ceramic is brittle. It requires a highly demanding installation. Improper installation is the primary human factor leading to seal damage, and it must be replaced.

Causes

Uneven installation of the stationary ring leads to vibration between the rotating and stationary rings. If this continues, this will cause chipping or breakage of the seal rings.

Solutions

Inspect the sealing before installation. Remove surface burrs and stains to ensure the sealing faces are clean.

During installation, a guiding structure should be provided for the O-rings to avoid scratching. Strictly control the leveling of the stationary ring to reduce operational vibration.

Conclusion

The failure of silicon carbide mechanical seals is not by chance, but r is attributed to certain details that have been ignored. Mastering the patterns of silicon carbide mechanical seal failure and solutions is an effective way to extend the service life of the sealing components.

Need more information about silicon carbide mechanical seals and their practical cases? Feel free to contact Newthink New Materials. Newthink is an advanced ceramics manufacturer with 14+ years of experience. We provide various silicon carbide mechanical seals to ensure the stable operation of equipment across major industrial sectors.

Thanks for your reading. Hope this article will be helpful.

FAQs

1. Which is better, silicon carbide or tungsten carbide mechanical seal?

Silicon carbide is better for high-temperature and corrosive environments. Tungsten carbide is tougher, better for high-pressure applications.

2. What are the 2 main types of mechanical seals?

Component seals and cartridge seals. Component seals require manual alignment for installation. Cartridge seals are pre-assembled, simplifying installation.

3. Can a mechanical seal run dry?

No. Dry friction causes wear and thermal cracking.

4. Should I lubricate a mechanical seal?

Yes. It is essential to form a protective film that reduces friction and wear.

5. What should I do before installing a new mechanical seal?

Inspect the sealing for damage first. Clean the faces to remove burrs or stains. Ensure all fasteners and O-rings are compatible with your specific media.

6. How tight should a mechanical seal be?

Fasteners must be tightened to prevent loosening. But avoid excessive pressure on the brittle ceramic faces.

7. What kind of oil do you use for mechanical seals?

Depend on the media and operating temperature. Use a clean, compatible barrier fluid or lubricant. Often, a low-viscosity hydraulic oil or specialized synthetic lubricant is used.

Reference

[1] Chen, C. Y., Wu, B. H., Chung, C. J., Li, W. L., Chien, C. W., Wu, P. H., & Cheng, C. W. (2013). Low-friction characteristics of nanostructured surfaces on silicon carbide for water-lubricated seals. Tribology Letters, 51(1), 127-133.

[2] Mayer, E. (2013). Mechanical seals. Butterworth-Heinemann.

[3] Sharma, S. K., Kumar, B., & Kim, Y. W. (2016). Tribological behavior of silicon carbide ceramics-a review. Journal of the Korean Ceramic Society, 53(6), 581-596.

[4] Zhao, X., Liu, Y., Wen, Q., & Wang, Y. (2014). Frictional performance of silicon carbide under different lubrication conditions. Friction, 2(1), 58-63.