Glossary

Thermal cycling is the repeated heating and cooling of a component, assembly, or joint as it moves between different operating temperatures over time. Each cycle causes the materials to expand when heated and contract when cooled, and because different materials (and even different sections of the same assembly) expand at different rates, the cycling creates repeated changes in stress, fit, and contact pressure.

In bolted joints and sealing applications, thermal cycling is important because it can change bolt preload and gasket stress from cycle to cycle. Differential expansion between bolts, flanges, and the clamped parts can temporarily increase or decrease clamp load, and repeated cycling can lead to embedment, creep/relaxation of softer materials, and gradual loss of sealing stress. Over time, thermal cycling can also contribute to fatigue damage (cracking) in fasteners or components, especially where stress concentrations exist, and it can accelerate issues like gasket leakage, loosening, or distortion if the joint design and materials aren’t matched to the temperature swings.