ASSESSMENT OF RESIDUAL STRESSES IN SINGLE-AND MULTI-BEAD-ON- PLATE WELDMENTS MEASURED BY NEUTRON DIFFRACTION

Welding residual stresses (RS) have important consequences for the performance of engineering components. Even when a weld can be produced successfully, the presence of RS must be taken into account when making an estimate of the useful working life of the component, since the mechanical properties of the weld joint, corrosion resistance and fatigue behavior can be impaired. For this reason it is desirable to estimate the RS state in the weld and surrounding area with as much precision as possible. The authors have used neutron diffraction to follow in detail the changes in the RS characteristics single- and multi-bead-on-plate welds in a low-carbon steel. This research has focused on: • the restraint condition applied during welding, • the effects at the start and end of the weld for a single bead, • the effect of post-weld heat treatment (PWHT) for a single bead, and • the effect of increasing the number of passes on the residual stress behaviour. The RS distributions are normalized by the yield strength of the material and compared with the distribution provided in fitness-for-purpose procedures. It is found that the current safety assessment procedure BS 7910 is significantly conservative, in particular for residual stresses transverse to the weld for weldments in the as-welded state. However the assumptions in BS 7910 for stresses remaining after post-weld heat treatment may not be completely conservative