THE ANALYSIS OF DISSIMILAR METAL WELD JOINT FORFRACTURE MECHANICS EVALUATIONS

摘要

This study is concerned with the stress analysis and fracture mechanics evaluation for a sub-critical crack inthe dissimilar metal weld (DMW). The DMW considered herein is a transition joint of the ferritic nozzle toaustenitic safe-end using the Inconel A 82/182 buttering and weld deposit. Weld residual stresses in the DMWnozzle are computed by non-linear thermal elasto-plastic analysis using the axisymmetric finite element (FE)model, for which temperature-dependent thermal and mechanical properties of the materials involved areconsidered. A stress relief in the as-welded nozzle by cold hydrostatic test is examined, and the operationpressure and thermal stresses are computed for normal service conditions. Computed residual and operationstresses are then mapped into a three-dimensional (3-D) domain by revolving the axisymmetric results, and linearelastic fracture mechanics (LEFM) parameters for a semi-elliptical surface crack in the combined stress state areevaluated using the finite element alternating method (FEAM). Results of and discussions on the stress analysisand fracture mechanics evaluations are presented. It is found that the effect of weld residual stresses on thecrack-driving forces is dominant, as high as three times or more than the operation stresses.