Structural components operating at high temperatures may fail due to the slow extension of a pre-existing crack in the structure over a period of time. For an elastic-secondary power law creeping material model, the stress and strain singularities at the crack tip can be controlled by a time-dependent loading parameter.[1] For long-term loading, the C*-integral parameter can be path-independent and applies to cracks only when the body with the crack undergoes extensive steady-state creep.