The increasing penetration of variable and unpredictable renewable energy sources into the liberalized electricity market brings about significant changes in the management strategies of fossil fuel power plants. These new operation modes cause remarkable effects on the lifetime of the plants. Consequently, the operators of the plants need to be assisted by effective procedures, which are able to define suitable production plans. In the present paper, the authors propose a dynamic model which can be used to estimate the effects of the variations of thermodynamic and mechanical parameters during transient operation, start-ups and shut-downs. To check the effectiveness of the model, a combined cycle plant with a three-pressure level heat recovery steam generator has been selected. The geometry of the components, the influence of the environmental conditions, and the control strategies are included in the model. In this way, the residual lifetime of the most critical components can be predicted.