Validated residual stress profiles for fracture assessments of stainless steel pipe girth welds

Abstract

Defect assessments for pressure vessels and piping are increasingly used to support the economic and safe management of operating plant. Assessments of defects in welds, however, can be highly sensitive to the through-thickness residual stress profiles assumed in the calculations. This is illustrated for typical stainless steel pipe girth welds where there is a lack of consensus in structural integrity procedures about what residual stress profiles to use. A general prescription for as-welded residual stress distributions in stainless steel pipe butt welds of arbitrary diameter and thickness, based solely on finite element studies, is critically examined by comparing the estimated profiles with an array of diverse weld residual stress measurements in pipe welds 16–110 mm thick. New ‘more realistic’ formulations for axial and hoop residual stresses are proposed that capture the profiles of both measured and predicted through-thickness residual stresses. They are suitable for use in fracture assessments, when supported by sensitivity studies, for structurally significant defects in non-stress relieved austenitic stainless steel girth welds, where the weld material overmatches the parent in terms of tensile properties. The formulations are validated for a range of weld groove geometries and weld processes, a thickness range of 16–110 mm, R/ t range of 1.8–25 and electrical heat inputs in the range 1.0–2.4 kJ/mm. The new approximations are simple to evaluate and suited for incorporation into structural integrity procedures.