Technical Advisory Group on the Structural Integrity review of the fatigue crack growth approach to transient cycles and other parameters used

TAGSI is the UK Technical Advisory Group for the Structural Integrity of high-integrity components (HICs) and has a role in reviewing specific technical questions from its sponsors through peer review utilizing independent experts. EDF-Nuclear Services (NS) asked TAGSI to review some proposed optimizations for calculating fatigue crack growth (FCG) and to provide some further insight into the basis of certain relevant parameters. The areas covered were as follows: numerical approaches to FCG evaluation using elastic-plastic cracked-body finite-element (FE) methods; the function of R-ratio term f(R) in RSE-M for ΔK_eff; and a new proposal for ordering and pairing transients aligned with plant operating conditions (POCs), referred to as the POC approach. This paper provides an overview of the review and associated discussions to address these questions. The main findings were as follows: TAGSI considers that the use of the ΔJ parameter for estimating FCG in the elastic-plastic regime is consistent with UK guidance, though some caveats and points for consideration were noted. Although the basis for the f(R) term in RSE-M is not well documented, some suggestions were made for how this may be better understood and developed. The POC method adopts a different approach to traditional methods for both the ordering and pairing of transients. TAGSI considers that the chronological POC approach (when including a modification, POC-mod, to combine start-up and shutdown transients) is an appropriate method for the ordering of transients for assessment. Some areas of non-conservatism were noted, to be assessed on a case-by-case basis.This article is part of the theme issue 'Future challenges for structural integrity of high-integrity components'.