When starting and shutting down steam turbines or changing their power outputs, steam temperature variations are bound to occur that lead to temperature differences in and between the components . These temperature differences result in free expansions of the components relative to each other, deformations of the components themselves, and stresses in the components lf such expansions, deformations and stresses exceed certain limits set by design features or the materials used, both immediate damage - axial or radial rubbing - and long-time damage - inadmissible permanent deformation and crack formation - may occur.

Being aware of the relevance of the problems, scientists and engineers have made numerous theoretical studies, laboratory and field experiments in the past years which led to a better understanding of the processes involved and the possible damages that may occur.

(1990)