A guide to BS 7910:2019 Annex P: it explains the physical meaning of the reference stress Ο_ref and the reference-stress method, the equivalence of Ο_ref and the limit load P_L, how it gives the FAD horizontal axis L_r, the general framework and net-section degradation, the plastic cut-off L_r,max and flow stress, and the calculation steps β with original diagrams and a live worked example.
Third of four problems on the welded A533B-1 plate: the HLAW specimen β as-welded, warmed to β30 β, with the load raised into the high load-ratio (large-plasticity) regime. We run it in mechCalc's BS 7910 Clause 7 fracture assessment calculator to see how the assessment calls plastic collapse once L_r=1.80 exceeds the cut-off value L_r,max, and why the relative weight of residual stress is diluted by plasticity at high L_r so that fracture toughness becomes the governing factor.