Investigation on tensile strain capacity of circumferential weld of X70 pipeline steel with softened heat affected zone

The circumferential welding joints of strain-based design X70 pipeline always fractured at heat affected zone in the tensile test. The crack driving force and fracture resistance curve of the circumferential welding joint defects were obtained by numerical simulation and impact toughness test separately. On the above basis, the considerable high strain capacity has been demonstrated by the tangent method and verified by wide plate tensile test. The results proved that the pipeline had considerable fracture resistance which may lead to high strain capacity and the crack driving force approach was more reasonable than current standard which required that the weld joint should not be fractured in the vicinity of the weld zone, and remitted the over-demand from material properties.