Improved procedure for computing residual stresses from neutron diffraction data and its application to multipass dissimilar welds

Neutron diffraction is an important tool for residual stress measurement in welded structures. The calculation of stresses from measured lattice spacings generally requires the stress free lattice spacing a priori. For dissimilar metal welds common to nuclear reactor pipeline systems, the stress free lattice spacing is a complex function of position due to the chemistry and microstructure inhomogeneity in the weld region, and its experimental determination can be both time consuming and unreliable. An improved approach is developed to calculate the residual stress field without the use of stress free lattice spacing. Its applicability is examined and justified in two multipass dissimilar metal welds made of 304L stainless steel plate and nickel alloy 82 filler metal using different heat inputs. The spatial variation in stress free lattice spacing is qualitatively discussed using the weld metal dilution mechanism. The improved approach is shown to be simple and practical for residual stress determination in dissimilar metal welds.