Definition(s)
Ratcheting
Progressive inelastic deformation or strain which can occur in a component that is subjected to variations of mechanical stress, thermal stress, or both (thermal stress ratcheting is partly or wholly caused by thermal stress). NOTE Ratcheting results in a plastic deformation, which increases by about the same amount at each cycle and quickly leads to an unacceptable value.
Source: API RP 17G, Recommended Practice for Completion/Workover Risers, Second Edition, July 2006 (Reaffirmed April 2011). Global Standards