Using ultrasonic and finite element for residual stress evaluation of a gas transmission pipeline

Once weld-induced residual stresses are mitigated, the risk of catastrophic failures in gas transmission pipelines is expected to decrease. Large-diameter pipelines are used extensively for gas transmission between cities. In large-diameter pipes, it is normal procedure to employ two or three welders working simultaneously to complete the joint. However, the number of welders, as well as the delay time, can influence the welding residual stress, which is considered in this paper. To this end, five welds completed with different welding procedures have been investigated on a large-diameter, 610 mm gas transmission pipeline. The welding residual stresses were measured using the ultrasonic method, a nondestructive stress measurement technique that works based on the acoustoelasticity law. The finite element method was also employed for modeling of the specimens in order to numerically validate the measurements. The results show that employing four welders welding simultaneously on a 610 mm diameter pipeline can considerably reduce the welding residual stress in comparison with a case of using one or two welders. Furthermore, a delay time between starting the segmental welding can create a preheating effect that leads to mitigation in the residual stresses.