EXPERIMENTAL-DETERMINATION OF THE RESIDUAL-STRESSES IN A SPIRAL WELD OVERLAY TUBE

Neutron diffraction was used to determine the residual stresses in a s piral weld overlay tube. The specimen was a 2.5 in. OD carbon steel tu be covered with a layer of alloy 625 weld overlay. Residual strains in the carbon steel and weld overlay layers were determined using the fe rritic (211) and austenitic (311) reflections, respectively. The resid ual stresses in each material were derived from the measured strains u sing Hooke's law and appropriate elastic constants. Tensile stress reg ions were found not only in the weld metal but also in the heat-affect ed zone in the carbon steel. The maximum tensile stress was located in the weld overlay layer and amounted to 360 MPa, about 75% of the 0.2% yield strength of the weld metal. The experimental data were compared with a finite element analysis based on an uncoupled thermal-mechanic al formulation. Overall, the modeling results are in satisfactory agre ement with the experimental data, although the hoop strain (stress) se ems to have been overestimated by the finite element model. Additional neutron diffraction measurements reveal that these welding residual s tresses vanished after annealing at 900 degrees C for 20 min. (C) 1997 Elsevier Science S.A.