Residual Stresses in Multi-Pass Gas Tungsten Arc and Laser Beam Welds

The residual stress states of the weld regions of gas tungsten arc and laser welded girth joints in 304 stainless steel cylinders were measured using neutron diffraction as a means to validated residual stresses predicted by finite element models (Sysweld) of the same weld protocols. These weld processes differ significantly in terms of total heat input, weld joint design, weld schedule, melting efficiency and resultant fusion and heat affected zone morphology. As a result the thermal history of these processes can be significantly different, resulting in differing mechanical response in terms of residual stress and distortion and ultimately in-service performance.  Residual stresses calculated from neutron diffraction strain measurements made transverse to the welds, indicate regions of peak tensile stresses adjacent to the weld fusion zone and a decrease directly within the weld centerline. Stresses become compressive in regions further from the weld region.  In comparison of the two weld techniques, narrower peak stress regions of greater magnitude were measured in the laser weld verses the arc weld. Furthermore, a rather unique set of neutron diffraction measurements of the circumferential variation of the residual stresses which were suggested by the 3D finite element model show strong variations of the hoop and axial stresses in the vicinity of the weld stop. This talk will present a critical comparison of the measurements and model results.