Spatial variation of residual stresses in a welded pipe for high temperature applications

Measurements of residual macro-stresses have been undertaken in a feature multipass circumferential single V butt-weld made from a P91 ferritic steel pipe over different spatial depths: (i) ≤10 μm by X-ray diffraction, (ii) ≤1 mm by incremental centre-hole drilling and (iii) through wall section using deep-hole drilling. The ability to make near-surface X-ray residual stress measurements on as-oxidised surfaces has been demonstrated and the implications for use in the evaluation of overall integrity are discussed. Each of the three measurement techniques provides complementary and consistent measurement of induced residual stresses for weld metal, heat affected zone and parent metal for the as-welded and the post-weld heat-treated conditions over the complete spatial range. The results are discussed with respect to the importance of the weld capping run in introducing near-surface compressive residual stresses, the through-wall profiles of the residual stresses measured at the weld metal position in hoop and axial directions and the presence of existing surface oxide.