Summary
Fatigue cracking is a mechanical form of degradation that occurs when a component is exposed to cyclical stresses for an extended period, often resulting in sudden, unexpected failure.
Examples from API 571 of fatigue caused by cyclic loading are:
thermal cycling in daily operation (e.g. decoking, intermittent service)
pressure cycling in daily operation (e.g. pressure swing absorbers).
Fatigue by cyclic loading is an age related damage mechanism.