Effect of stress-relief annealing on the fatigue properties of X80 welded pipes

Highlights: • Effect of annealing on the fatigue properties after plastic deformation was studied. • The plastically deformed X80 pipe has the highest fatigue life after annealing. • Stress-relief annealing has a greater recovering effect on the high-energy dislocations. • High-energy dislocation motion results in the change in fatigue properties. Welding and mechanical expansion during the manufacture of X80 pipes can introduce and change the residual stress at welding joints, which has many adverse effects on the fatigue properties of in-service pipelines that experience cyclic stress due to pressure fluctuations. Stress-relief annealing is an effective way to change the residual stress distribution. In this work, changes in the strength, residual stress, and fatigue properties of original and plastically-deformed X80 welded pipes were compared after stress-relief annealing. The results showed that stress-relief annealing significantly improved the fatigue lives of the welded joints of X80 pipes, especially when performed after plastic deformation. High-energy dislocation motion was the main cause of changes in the residual stresses and fatigue properties, as shown by the changes in dislocation distribution and misorientation within grains.