Stress reduction and evaluation methods for pipeline girth weld

Residual stress occurs in the girth weld zone after welding, which reduces the effective bearing capacity and safety margin of the pipeline. It is of great engineering value to select effective stress reduction strategies and evaluation methods to ensure the service safety of welded pipe sections. The ultrasonic impact stress reduction technology and the coercive force based on stress evaluation technology were applied to the X80 welded pipe section with girth welds. The microstructures, the residual stress and mechanical properties of the welded area before and after reduction were compared. The results show that the microstructures at the fusion line of weld toe before reduction take on a laminar banded distribution. After reduction, the grains become smaller and transform into the intertwined distribution, and the grain distribution is more uniform. The coercivity value of the welded center decreases generally, the residual stress changes from the tensile stress to the compressive stress, and the stress concentration decreases. Mechanical properties, especially the impact toughness increases by 13%-21%, but the tensile properties change little. The stress level of the circumferential weld of the pipeline in service decreases significantly after the ultrasonic impact. The ultrasonic impact and coercivity methods are effective means for stress reduction and evaluation of girth welds in oil and gas pipelines. © 2022 University of Petroleum, China. All rights reserved.