A procedure for treating secondary stress in failure assessment diagram

Abstract

The CEGB R6 Rev.3 failure assessment method, for structures containing defects subjected to combined primary and secondary loads, is widely adopted all over the world. A set of ϱ factors, which was derived by Ainsworth according to a deformation bounding theorem and the concept of reference stresses, has been given in the revision. However, the results obtained with those ϱ factors are unsafe when a small defect is located within a high tensile residual stress zone, and are over-conservative in other situations. In this paper, recommended ϱ values based on R6 option 1 are given by redefining the reference stress under pure secondary loads. The recommended ϱ factors overcome the above-mentioned shortcomings of R6 Rev.3. This procedure has been accepted in the Chinese “A Guidance of Safety Assessment for Pressure Vessel Containing Defects” (SAPV-95).