The increasing demand of reliable creep design for very long lives (exceeding 100.000 h), as those for high stress-low temperatures and high temperature-low stress regimes, requires a model formulation capable to account for the nonlinearity in the stress dependence of the logarithm of the creep rate as a result of the combination of both diffusional and dislocation type creeps. In this paper, a creep model, where the effect of mechanism change has been accounted for through an explicit dependence of the creep exponent n on stress, has been proposed. The model has been also extended, incorporating damage processes and characteristics of tertiary creep stage, adopting a time independent damage formulation proposed by the authors. An application example of the proposed approach to high purity aluminum is given