Engineering components which are considered in safety case assessments contain either real or hypothetical crack-like defects that experience combinations of primary and secondary stresses during service. A number of assessment procedures contain simplified numerical approaches to detail the interaction of these stresses under in-service or fault conditions including the R6 procedure used in the UK and the RSE-M Appendix 5.4 (RSE-M) assessment code adopted in France.

The R6 procedure and RSE-M approaches are shown to be relatively similar for cases which do not contain secondary loading but differ when treating secondary stresses. It is generally accepted that the R6 procedure in terms of ρ or V is conservative compared to finite element analyses and plant experience; which has driven the development of a new formalism of the R6 V factor, Vg. This new formalism is seen to be more aligned to the RSE-M approach but differs in some cases.

The aim of this paper is twofold: 1) to demonstrate the main divergence between the procedures, and 2) to provide experimental comparison between the R6 V, the newly formalised Vg, and the RSE-M approaches under test cases within literature that contain combined primary and secondary loading.

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