Effect of strength mismatch on limit load of dissimilar metal welded joint for connecting pipe-nozzle of nuclear pressure vessel

Abstract

The interface region cracks in dissimilar metal welded joint (DMWJ) for connecting pipe-nozzle of a reactor pressure vessel (RPV) to safe end are important concerned cracks in fracture assessment. In this work, based on a large amount of finite element analyses, the effect of strength mismatch on the limit loads of two interface cracks in an actual DMWJ has been investigated for wide ranges of strength mismatch factors and crack sizes. The results indicate that for shallower cracks, the limit load is dominated by fully yielding of the safe end pipe and are independent of strength mismatch and crack size. For deeper and longer cracks, the limit load is dominated by fully yielding of the ligament area materials. As the mismatch factor M increases from undermatch (M < 1) to overmatch (M > 1), the limit loads increase. To improve the load-bearing capacity of the DMWJ and prevent plastic collapse failure, a high degree of strength overmatch (increasing strength of buttering and weld metals) should be designed and adopted. The normalized limit load solutions as functions of mismatch factor and crack size have been obtained for the two interface cracks.