Flaw Evaluation for PWR and BWR Component Weld Joints Using Advanced FEA Modeling Techniques

Abstract

Primary Water Stress Corrosion Cracking (PWSCC) of Pressurized Water Reactor (PWR) primary loop piping/nozzle Dissimilar Metal Weld (DMW) joints and Inter Granular Stress Corrosion Cracking (IGSCC) of Boiling Water Reactor (BWR) weld joints is an ongoing issue in the nuclear power industry. Recent field experiences with PWSCC of various DMW joints in US plants led to the development and application of an Advanced Finite Element Analyses (AFEA) methodology that permits crack propagation with a natural flaw shape. Crack growth and fracture evaluations for both PWR and BWR components are generally performed based on a conservative, idealized crack shape model, e.g. semi-ellipse, rectangle, etc., depending on the geometry of the crack and the component. Conventional evaluation methodologies and/or assumptions of this kind, in some cases may provide excessive conservatisms. The use of natural flaw shape development with crack propagation might provide a more realistic assessment of crack growth and structural integrity. The prime purpose of this study is to demonstrate the conservatism/margins in the conventional “idealized crack shape” methodology. A comparison study of crack growth behavior between the applications of the idealized and natural crack shape methodologies has been performed in order to assess the level of conservatism/margins in the conventional crack growth evaluation methodology and the possible impacts on the structural integrity evaluation for both PWR and BWR components. Comparison studies on the impacts of the differences in crack growth law and loading condition used for crack growth evaluations have been performed as well.

Interaction of Mechanical Heterogeneity and Residual Stress on Mechanical Field at Crack Tips in DMWJs

“…Furthermore, sometimes, the residual stress might exceed the yield strength of the base metal and the weld metal [25,26]. And the residual stress of the DMWJ is more of a concern for SCC than the working load [27][28][29][30]. However, the influence of the interaction between the mechanical heterogeneity and the residual stress on the crack tip mechanical field is unclear.…”

Numerical investigation on stress corrosion cracking behavior of dissimilar weld joints in pressurized water reactor plants

“…The distribution of residual stress [12] is shown in Fig.4. Note that only the hoop stress for an axial crack was applied in the weld region.…”