Fracture toughness of welding joints in oil and gas pipelines under welding restraint conditions

In the welding process of tying-in seam and golden weld in oil and gas pipelines, golden welding joint is the weak point and is prone to leaking and cracking due to strong grouping, complex working conditions and higher restraint stress. In order to increase the fracture toughness of welding joints, a self-restraint welding device was designed in this paper to simulate the golden welding process under different restraint conditions. And then, the Crack Tip Opening Displacement (CTOD) value of welding joints was tested and calculated. It is shown that the CTOD valve of weld zone under restraint conditions has little difference with that in free state, and the CTOD valve of heat affected zone is significantly lower than that in free state. Besides, the greater the restraint stress, the lower the CTOD value and the worse the toughness. When oil and gas pipelines are welded under restraint conditions, the cracking resistance of welding joints is reduced to a certain extent. Therefore, it is recommended to reduce the restraint stress as much as possible during golden welding to decrease the adverse effect on the fracture toughness of welding joints.