Fracture Toughness of Different Locations of Spiral Submerged Arc Welded Joints in API X80 Pipeline Steels

API X80 pipeline steels have been widely used in long-distance transportation of oil or natural gas under high pressure due to their high transportation efficiency, low energy loss and low production cost. While the fracture toughness of welded joints are harder to measured. In this paper, J-integral resistance curves of Spiral Submerged Arc Welded (SSAW) joints were examined at different locations of the BM, WM and HAZ. The grain coarsening induced by welding thermal cycling leaded to weaker toughness in WM and HAZ than the BM. The optical microscope (OM) and scanning electron microscope (SEM) were used to analyze the fracture mechanism.