Results of finite element calculations and neutron diffraction measurements of residual stress distributions in a component welded from hollow square section inconel tubes are presented. In the finite element analysis, plane deformation conditions were assumed. The material is assumed to be thermoelastic--plastic with temperature dependent material properties. The mechanical field is coupled to the temperature field only through the temperature dependent constitutive properties and the thermal strain. The plane deformation formulation differs from the ordinary plane strain formulation only in the nodal displacement-strain relationship. This difference is that epsilon 33instead of being zero is computed from the equation epsilon 33 = beta sub 1 + beta sub 2 x sub 1 + B sub 3x2 where beta sub 1 , beta sub 2 and beta sub 3 are constants. These constants add three unknowns to the system of equations in the FE-analysis. To validate the calculations, the computed strains are compared with measured strains. The measurements were made at ten points between two of the welds in three orthogonal directions, using the neutron diffraction technique. The neutron technique differs from the X-ray diffraction method in that neutrons can penetrate substantial distances into the interiors of components which X-rays cannot. This penetration makes it possible to measure through thickness strain variations. In the results one can see that this plane deformation analysis predicts the actual strains and stresses much better than the plane strain analysis. Comparison between these plane deformation results and earlier results from a three-dimensional analysis is also done.