Assessment of creep rupture life of weldments of martensitic steels

Abstract

Abstract Martensitic steels are of major importance for modern high efficient power plants. Their long-term creep rupture characteristics are essential for the economic and reliable design of high temperature components. However, the weldments in such components have to be considered as a potential failure area under long-term creep loading as the heat affected zone of ferritic creep resistant materials (for example new martensitic steels) is exposed to significant microstructural changes due to the heat input during welding. Furthermore, the stress situation and multiaxiality of the stress state in the weld region changes permanently due to creep and relaxation. Evaluation therefore has to be based on experimental investigation that means uniaxial creep tests of crossweld creep specimens. The microstructrural characterisation of the heat affected zone and the comparison with the situation in the optimised base material has also to be taken into account. Heat affected zone simulation of specimens and the relevant experimental investigation deliver an important basis for the modelling of the stress – strain situation. All these aspects have to be combined in the inelastic computation in order to consider all relevant effects: the individual creep strength in the different regions of the heat affected zone as well as the influence of the subsequent state of stress multiaxiality. The paper highlights recent and on-going research activities in Germany in this domain. It also demonstrates the importance of inelastic calculation for the design of welded pipes.