Thermal Assault in Mechanical Seals: Damage Mechanisms and How to Prevent Failures
Thermal assault is one of the most underestimated causes of mechanical seal failure. Even short temperature spikes can damage seal faces, elastomers, and metal hardware—often without obvious warning at the beginning. Once the seal loses face flatness or lubrication stability, leakage and shutdowns become much more likely.
This article explains what thermal assault is, why it destroys mechanical seals, what damage it causes, and the most practical ways to reduce thermal stress in real pumping systems.
What Is Thermal Assault in Mechanical Seals?
Thermal assault means excessive or uncontrolled heat exposure that pushes seal components beyond their safe operating limits. It can happen in several ways:
- Sudden start-up without proper flooding
- Dry running or loss of flush flow
- Rapid temperature cycling (hot to cold, cold to hot)
- High friction from face contact or poor lubrication
- Chemical reactions that accelerate at higher temperatures
A key point many users miss: small temperature changes can trigger big problems, especially when they happen repeatedly or quickly.
Why Heat Is a “Failure Accelerator”
Heat does more than just raise temperature. It can amplify multiple failure modes at once:
- Speeds up chemical corrosion and oxidation
- Weakens elastomers and reduces flexibility
- Changes face contact conditions by thermal expansion
- Breaks down lubrication film and increases friction
- Creates thermal gradients that distort seal geometry
In real service, thermal assault rarely acts alone—it often combines with vibration, abrasives, or chemical attack and makes the seal fail much faster.
Where Thermal Damage Happens First
1) Elastomers (O-rings and Secondary Seals)
Elastomers are usually the first to suffer because they are sensitive to temperature and chemicals.
Common symptoms include:
- Hardening and loss of elasticity
- Swelling or shrinkage from fluid incompatibility
- Cracking or permanent compression set
- Blistering or surface degradation
Once elastomers lose sealing ability, leakage paths appear even if the seal faces look acceptable.
2) Seal Faces (Rotary and Stationary)
Seal faces must stay flat and stable to keep a thin lubricating film. Thermal assault can disrupt this balance and lead to:
- Face distortion from uneven heating
- Micro-cracks caused by rapid thermal cycling
- “Hot spots” that produce glazing or uneven wear
- Increased friction and accelerated face scoring
When face flatness is damaged, the seal may leak intermittently at first, then fail permanently.
3) Metal Hardware (Springs, Bellows, and Drive Parts)
High heat can weaken mechanical parts or change their performance:
- Reduced spring force or loss of tension
- Distorted metal parts affecting alignment
- Increased risk of corrosion in aggressive media
- Loss of mechanical stability under high load
If hardware becomes unstable, face loading becomes uneven and the seal enters a rapid failure cycle.
Typical Thermal Assault Triggers in Pump Systems
Thermal assault often occurs due to operating conditions, not poor seal quality. Common triggers include:
Dry Running
The most destructive condition because there is no liquid film to cool and lubricate the faces.
Low-Pressure Zones and Vaporization
Low seal chamber pressure can create vapor pockets that break lubrication and increase face contact.
Poor Flush or Quench Management
Blocked lines, wrong flow direction, or incorrect piping plans can cause heat to build up rapidly.
Abrasive Slurries
Abrasives raise friction, reduce film thickness, and create heat at the sealing interface.
Temperature Cycling
Repeated hot/cold changes create micro-stress and fatigue damage over time.
Damage Patterns You Can Recognize
If a seal fails from thermal assault, inspection often shows one or more of these signs:
- Heat checking: fine cracks or “crazing” on the face surface
- Blistering or burnt appearance on carbon faces
- Glazing: shiny or polished areas caused by overheating
- Elastomer hardening or cracking
- Severe wear combined with discoloration
Thermal assault failures often look “sudden,” but the damage process builds quietly over time.
Practical Ways to Prevent Thermal Assault
1) Use Correct Materials for Heat and Chemistry
Material selection should match temperature + fluid + abrasives, not just pump size.
Recommended options for tougher services:
- SiC vs SiC for high heat and abrasives
- SiC vs Carbon for controlled wear and stability
- High-temperature elastomers where suitable (for example, upgraded FKM grades)
If the application is corrosive or abrasive, choosing the wrong face material can dramatically increase heat damage risk.
2) Apply a Proper Flush Plan
A stable seal needs cooling and clean lubrication. Use appropriate piping plans where applicable:
- Plan 11 (recirculation) for basic cooling
- Plan 21 / 23 for improved heat control
- Plan 32 for clean external flush to protect faces
- Plan 62 quench for vapor control and heat buffering
The goal is simple: maintain lubrication, remove heat, and keep contaminants away from the faces.
3) Reduce Thermal Shock at Start-Up
Safe start-up reduces thermal stress dramatically:
- Ensure pump and seal chamber are fully flooded
- Open flush/buffer lines before running
- Confirm correct rotation with a short “bump”
- Warm up hot service slowly (avoid sudden temperature jumps)
- Watch for abnormal temperature rise in the first hour
4) Monitor Heat-Related Indicators
Many thermal failures can be prevented with basic monitoring:
- Temperature trends near gland or seal chamber
- Vibration trend changes
- Leakage pattern changes (mist → drip → flow)
- Oil condition (for submersible or oil chamber designs)
If you track trends early, you can stop before major damage occurs.
5) Improve Alignment and Surface Finish
Thermal assault becomes worse when the seal is already under stress. Make sure:
- Shaft run-out and bearing condition are within limits
- Seal chamber is clean and not distorted
- Gland is installed square and torqued evenly
- Seal faces are handled cleanly (never touch lapped faces)
Even a small installation error can turn a normal heat load into a seal killer.
Quick Checklist: Preventing Thermal Assault
- Avoid dry running at all times
- Keep flush and cooling lines clean and flowing
- Choose face materials suitable for heat + abrasives
- Use elastomers compatible with temperature and media
- Start up gently and avoid rapid temperature cycling
- Monitor temperature, vibration, and leakage trends
FAQ: Thermal Assault in Mechanical Seals
What is the main cause of thermal assault?
Dry running and loss of lubrication are the most common causes. Without a fluid film, heat builds instantly and damages faces.
Can temperature spikes really damage a seal quickly?
Yes. Even brief spikes can distort faces, cause micro-cracks, or harden elastomers, especially in repeated cycles.
Which seal face materials resist thermal assault better?
Silicon carbide is one of the best options for high heat and abrasive services. Tungsten carbide may be preferred when impact resistance is needed.
How can I reduce thermal shock during commissioning?
Flood the chamber, open flush lines first, verify rotation, and warm up hot services gradually instead of starting at full temperature.
Conclusion
Thermal assault is a silent failure driver in mechanical seals. It accelerates chemical attack, reduces lubrication stability, and damages both faces and elastomers. The best protection comes from smart material selection, correct flush plans, gentle start-up practices, and simple monitoring.
If you need help selecting mechanical seal materials or upgrading a seal for high-temperature service, feel free to contact Hongteng Seals Co., LTD.
