Reactor pressure vessels of nuclear installations are subjected to operating parameters that lead to a change in material and flaw state. The safety margin of both the material for older vessels and the optimized material has to be quantified with reference to extremely long-term effects. Research programs in West Germany are focused on assessing criteria for the applicability of small-scale specimen testing to component behavior under all realistic and postulated loading conditions. The problem will be treated theoretically and experimentally for a wide range of materials, including the worst-case material state at the end of life.