This paper is to present the structural integrity analyses for a preemptive weld overlay in a pressurizer surge nozzle. Based on ASME Code Case N-504-3 and MRP-169, the full structural weld overlay sizing calculation, residual stress improvement analysis, shrinkage evaluation, fatigue crack growth analysis and fatigue usage analysis were performed. After weld overlay installation, the welded nozzle structure has to be analyzed to measure the improvement in residual stresses around the inner surface of the original weld. The residual compressive stress distribution is thus addressed to be resistant to subsequent stress corrosion, the initiation of cracking, and the further crack growth. To ensure the structural integrity of the attached piping system, the weld induced displacement is measured and transformed to temperature gradient to simulate the shrinkage after overlay welding and to analyze the post-weld distortion and stress situations. Based on the further comparisons of fatigue crack growth with all of system operating cycles, two surface cracks in the original weld are conservatively postulated. Additionally, both the stress limits and cumulative fatigue usages of the nozzle with weld overlay are evaluated to meet the design requirements of ASME Code Section III. The present analysis results confirm the effectiveness of the procedure for analyzing the structural integrity of a nozzle with weld overlay.

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