Abstract In the future, the energy supply will strongly fluctuate, which results in more frequently load cycles. For this reason, it is necessary to analyze fatigue crack growth under the aspect of reasonable load cases in relevant power plant components. Therefore, numerical three-dimensional fatigue crack growth simulations for different power plant components have been performed using FRANC3D taking temperature transients and pressure loads as well as different relevant crack positions into account. The results show that the temperature gradient of thermal loadings has a large influence on stress intensity factors (SIF) and may lead to much higher SIF than under pure mechanical loading. In order to quantify the residual lifetime, temperature-dependent fatigue crack growth curves for different stress ratios were experimentally determined. Therefore, experiments with constant temperatures between room temperature and 600°C have been performed using C(T)-specimens cut of a decommissioned high-pressure bypass station made of the ferritic-martensitic steel X20CrMoV12-1. The investigations show that crack growth rates rise in the PARIS-regime under higher temperatures. The data were finally used to extract a(N) -curves from numerical results in FRANC3D.