A structural integrity assessment procedure for welded structures with weld metal strength mismatch

Structural integrity assessment procedures, such as the GE/EPRI scheme, CEGB R6 and the PD 6493:1991, are frequently applied to welded structures where cracks are located either in the weld or in the heat affected zone. Since the development of those procedures assumed homogeneous mechanical properties, their application to welded structures can lead to inaccurate predictions. This paper focuses on the effect of weld strength mismatch on structural integrity assessment. To make connections with current practice, the authors examine the accuracy of PD6493:1991 when applied to welded structure with weld metal strength mismatch. The authors demonstrate that the Level 2 assessment in PD6493:1991 can be either conservative or non-conservative, depending on the geometries and loading conditions being evaluated. Finite element analysis of several commonly-used structures reveals that the failure assessment curves of a structure with different degrees of weld metal mismatch can be scaled to the failure assessment curve of the same structure with homogeneous mechanical properties. This scaling allows the use of the GE/EPRI procedure for the structural integrity assessment of welded structure with significantly improved accuracy as compared with PD6493:1991 Level 2. The incorporation of the weld metal strength mismatch effect on the limit loads and the use of the failure assessment diagram are responsible for such improvement