Thermal shock and thermal fatigue are two common, but different ways temperature changes can damage heat exchangers and other thermal process equipment. One happens fast and is often obvious – the other builds quietly over time.
Understanding the difference matters. It affects how equipment is designed, how it’s operated, and how failures show up in the real world.
This guide breaks down what thermal shock and thermal fatigue are, how they affect heat exchangers, and what you can do to reduce the risk of both.
What Is Thermal Shock?
Thermal shock is a design issue, not just an operating issue. It occurs when equipment experiences a sudden temperature change it wasn’t designed for. For example, rapidly switching from heating to cooling.
Metals expand when heated and contract when cooled. When that temperature change happens too quickly, different parts of the equipment heat up or cool down at different rates. The result is rapid development of thermal stress inside the metal.
If that stress is high enough, it can cause immediate physical distortion or damage.
What Thermal Shock Looks Like in Practice
- A channel plate distorts during rapid heat-up
- Distortion reduces gasket compression, causing a leak
- Components move, creak, or “pop” as the metal shifts
These changes happen quickly—and operators can often see, hear, or feel them as they occur.
Thermal shock is tied closely to startup, shutdown, and process upsets, which is why ramp rates and operating procedures matter so much.
What Is Thermal Fatigue?
Thermal fatigue is different. It happens when equipment is exposed to repeated heating and cooling cycles over time.
Each cycle puts the metal into tension and compression. One cycle usually isn’t a problem. Hundreds or thousands of cycles are.
Eventually, those repeated stresses add up and cause fatigue cracking, even if each individual temperature change was within design limits.
What Thermal Fatigue Looks Like in Practice
- A crack slowly develops in the tube-to-tube sheet weld
- The crack grows with each heat cycle
- One day, a tube separates and starts leaking
Unlike thermal shock, thermal fatigue usually doesn’t announce itself. Operators rarely see it coming until a leak appears or a test fails.
How Thermal Shock and Thermal Fatigue Affect Heat Exchangers
Heat exchangers are designed to handle temperature differences, but those same conditions must be properly accounted for to manage thermal shock and thermal fatigue.
Distortion and Immediate Leaks (Thermal Shock)
Rapid heating or cooling can cause uneven expansion between:
- Tubes and shell
- Channel covers and tube sheets
- Gaskets and sealing surfaces
That mismatch can distort components and lead to leaks during startup or process changes.
Fatigue Cracking at Welds and Joints (Thermal Fatigue)
Welded joints, especially tube-to-tube sheet connections, see repeated stress as equipment heats and cools. Over time, this cycling can initiate cracks that grow until failure occurs.
Gasket and Seal Degradation
Sealing materials are especially sensitive to rapid temperature swings and repeated cycling. Thermal shock can cause immediate leakage, while thermal fatigue can shorten gasket life through gradual loss of resilience.
How Design Plays a Role in Preventing Thermal Shock and Fatigue
Both thermal shock and thermal fatigue are influenced heavily by design decisions made early. When real operating conditions are known—startup ramp rates, temperature swings, flow changes, and seasonal variations—designers can account for them by selecting:
- Appropriate materials
- Wall thicknesses
- Tube layouts
- Expansion allowances
Designing for actual conditions reduces stress concentrations and helps equipment handle both sudden temperature changes and long-term cycling.
How to Reduce the Risk of Thermal Shock and Fatigue
Operators and engineers can take practical steps to limit damage:
- Ensure appropriate design spec from the start
- Warm up and cool down equipment gradually
- Avoid sudden slugs of hot or cold fluid
- Use control valves or automation to manage ramp rates
- Follow startup and shutdown procedures closely
- Confirm cycling frequency and temperature ranges during design
- Choose materials suited for thermal cycling
Thermal shock and thermal fatigue don’t fail equipment in the same way, and treating them as the same problem can lead to missed risks. When you understand what fails fast versus what fails quietly, you can:
- Improve startup reliability
- Reduce unplanned maintenance
- Extend equipment life
- Avoid surprises during operation or testing
Want help reviewing your operating conditions or making sure your next design accounts for both thermal shock and thermal fatigue? Start the conversation today.
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