Thermal Shock in Heat Exchangers
Thermal shock from rapid temperature changes can crack heat exchanger plates and tubes. Learn what causes it, how to prevent it, and which materials are most vulnerable.
What is Thermal Shock?
Thermal shock occurs when different parts of a heat exchanger expand or contract at different rates, creating internal stress. If the stress exceeds the material's strength, the component cracks or warps.
It is caused by rapid temperature changes: starting up with hot fluid into a cold exchanger, adding cold fluid to a hot exchanger, or sudden loss of one fluid flow while the other continues.
Vulnerable Materials
- Glass-lined steel: The glass lining is brittle and cracks easily from thermal shock. Maximum temperature change: 50 degrees C.
- Graphite: Graphite heat exchangers are extremely vulnerable. Maximum temperature change: 30 to 50 degrees C.
- Thin stainless steel plates: PHE plates are thin (0.4 to 0.8mm) and can warp from rapid temperature changes, causing gasket leaks.
- Cast iron: Brittle. Cracks from thermal shock, especially when cold water hits a hot surface.
Prevention
- Start up slowly. Introduce the hot fluid gradually, allowing the exchanger to warm up uniformly.
- Never start cold fluid flow into a hot exchanger. Always start the hot side first, then gradually introduce the cold side.
- When shutting down, stop the hot side first, then the cold side after temperatures have stabilised.
- Install temperature ramp controllers for automated startup sequences.
- Use materials with lower thermal expansion coefficients or higher thermal shock resistance for demanding applications.
- Install check valves to prevent backflow when one pump stops, which can cause sudden temperature reversals.
Steam to cold water is the most dangerous
Introducing steam into a cold heat exchanger causes immediate boiling and violent temperature gradients. The resulting thermal shock can crack plates, distort frames, and blow out gaskets. Always warm up the exchanger with hot water or gradually reduce steam pressure before introducing full-pressure steam.
Tip: Train operators on the startup and shutdown sequence for every heat exchanger. Post the sequence on a laminated card near the equipment. Most thermal shock damage occurs during startup, not during normal operation.