Developments in the R6 defect assessment procedure: the treatment of combined primary and secondary loading

This article reviews ongoing developments related to the treatment of secondary stresses in low-temperature fracture such that best practice and pertinent information are identified. The article also provides an overview of the recent developments within R6 Section II.6 related to the treatment of combined primary and secondary loads in fracture. In recent years, there has been considerable activity on work associated with understanding the effect of secondary stresses on fracture. Here, secondary stresses are defined as displacement-controlled stresses, such as thermal and weld residual stresses (WRS) that do not contribute to plastic collapse. The consideration of such secondary stresses is crucial to the ongoing justification of high-integrity components. The range of work internationally that has focused on the treatment of secondary stresses includes work performed as part of the R6 development programme, work within other UK national programmes into fracture and work published internationally in the open literature, for application within the R6 procedure. Given the wide range of activities and potential developments elsewhere, it is considered timely to provide a review of the recent work to understand the areas of progress, relative strengths and weaknesses and potential gaps in understanding. This understanding has also led to a further refinement of the methods within R6, with a new Section II.6 currently being drafted, details of which are included herein.This article is part of the theme issue 'Future challenges for structural integrity of high-integrity components'.