The effect of welding method on the fracture toughness of X90 pipeline girth weld joints

With the continuous increase in energy demand in China, the research and development of new generation high-grade pipeline materials has become a hot topic. And X90 pipelines have gradually become the focus of research. However, they have not yet been officially put into use. In the actual construction of oil and gas pipelines, the girth welded joint of the pipeline is a weak link. The welding quality is crucial to ensure the safety of long-distance oil and gas pipelines, and the welding method plays a decisive role in the welding quality of the pipeline. Therefore, it is necessary to study the effect of welding method on the fracture toughness of X90 pipeline girth welded joints and clarify the fracture performance of X90 pipeline girth weld joints. This provides theoretical guidance for the formal use of the X90 pipeline in practical engineering, and also provides technical support for the welding assessment of the X90 pipeline. In order to accurately obtain the fracture toughness of X90 girth welded joints, an improved regularization method was used to test the SENT specimens of X90 girth weld joints for fracture toughness. To accurately obtain the fracture toughness of the X90 circumferential welded joint, an improved regularization method was used to test the SENT specimen of the X90 circumferential welded joint for fracture toughness. Test specimens were extracted from X90 pipeline circumferential welded joints welded by manual welding, self-shielded flux-cored semi-automatic welding, and gas-shielded flux-cored semi-automatic welding, respectively, and fracture toughness tests were conducted. The results showed that the resistance curve obtained from the specimens with shallow cracks is lower than that obtained from the specimens with deep cracks under the same welding method. The specimens with deep cracks in the heat-affected zone have the highest resistance curve, while the specimens with shallow cracks in the heat-affected zone have the lowest resistance curve. The weld zone specimens were prone to brittle fracture during the test and had relatively poor fracture performance. Furthermore, they were greatly influenced by the welding method, with all of the weld zone specimens welded with gas-shielded flux-cored semi-automatic welding experiencing brittle fracture. Therefore, gas-shielded flux-cored wire semi-automatic welding needs to be optimized as a reference method in practical X90 pipeline engineering applications, which is crucial for maintaining the integrity of the X90 pipeline structure.