Research on Mechanical Properties of Steel Girth Welds of X80 Pipeline in Service

In order to reduce the failure of circumferential welds of oil pipelines and improve the safety of oil and gas pipelines in China, a series of mechanical properties of circumferential welds of in-service Sino-Myanmar natural gas pipelines were studied, and the tensile bearing test of circumferential welds with cracks was carried out through prefabricated cracks. The results show that the tensile strength, bending resistance and hardness of the girth weld meet the standard requirements. But the impact test results of girth weld center and heat affected zone show that the toughness is poor. In addition, with the increase of defect height, the bearing capacity of the girth welds with defects without fatigue precracking shows a linear decline trend, while the bearing capacity of the girth welds with fatigue precracking shows an accelerated decline trend. With the increase of the simulated crack depth, the failure stress of the small sample with defective girth weld showed a decreasing trend. The tensile strength of the samples without defects is basically higher than the failure stress of the samples with defects. But the impact test results of girth weld center and heat affected zone show that the toughness is poor. In addition, with the increase of defect height, the bearing capacity of the girth welds with defects without fatigue precracking shows a linear decline trend, while the bearing capacity of the girth welds with fatigue precracking shows an accelerated decline trend. With the increase of the simulated crack depth, the failure stress of the small sample with defective girth weld showed a decreasing trend. The tensile strength of the samples without defects is basically higher than the failure stress of the samples with defects.