Some issues on creep damage modelling of welds with heterogeneous structures

Abstract

Welded components are used widely in power plants. Many of these components operate at high temperatures and under high pressures. Defects or micro cracks may be found in the vicinity of the welds. These micro cracks or voids can grow under creep cracking conditions. These cracks are often found in a narrow zone close to the interface between the parent material and the heat-affected zones (HAZ), known as the type IV region, or in some cases, in the weld metal. Welds are metallurgically complex, with heterogeneous structures within the weld metal and the HAZ. It is important to have knowledge of the initial metallurgical features and the associated material property variations so that it may be possible to accurately model the possible failure modes of welds using, for example, finite element (FE) numerical modeling techniques. This paper describes a procedure related to the determination of the high temperature creep properties for each sub-region of welds from experimental results, and it also describes the subsequent failure modeling of welds, using a creep damage mechanics approach in FE analyses. Typical examples, for P91 welds in power plant, are used to illustrate the applications.