Engineering tools for robust creep modelling

High temperature creep is often dealt with simplified models to assess and predict the future behavior of materials and components. Also, for most applications the creep properties of interest require costly long-term testing that limits the available data to support design and life assessment. Such test data sets are even smaller for welded joints that are often the weakest links of structures. It is of considerable interest to be able to reliably predict and extrapolate long term creep behavior from relatively small sets of supporting creep data. For creep strain, the current tools for model verification and quality assurance are very limited. The ECCC PATs can be adapted to some degree but the uncertainty and applicability of many models are still questionable outside the range of data. In this thesis tools for improving the model robustness have been developed. The toolkit includes creep rupture, weld strength and creep strain modeling improvements for uniaxial prediction. The applicability is shown on data set consisting of a selection of common high temperature steels and the oxygen-free phosphorous doped (OFP) copper. The steels assessed are 10CrMo9-10 (P22), 7CrWVMoNb9-6 (P23), 7CrMoVTiB10-10 (P24), 14MoV6-3 (0.5CMV), X20CrMoV11-1 (X20), X10CrMoVNb9-1 (P91) and X11CrMoWVNb9-1-1 (E911). The work described in this thesis has provided simple yet well performing tools to predict creep strain and life for material evaluation, component design and life assessment purposes. The uncertainty related to selecting the type of material model or determining weld strength factors has been reduced by the selection procedures and by linking the weld behavior to the base material master equation. Much of the resulting improvements and benefits are related to the reduced requirements for supporting creep data. The simplicity and robustness of the new tools also makes them easy to implement for both analytical and numerical solutions.