Investigation on Mechanical Properties of X80 Pipeline Girth Weld Welded by Semi-Automatic and Automatic Welding

The traditional manual welding in pipeline construction is being gradually replaced by semi-automatic and automatic welding in China. Semi-automatic welding is especially applied to X80 pipeline girth weld welding widely. Compared with semi-automatic welding, automatic welding has features of more efficiency, better quality and higher reliability. As the strength of pipeline steel increasing and the length, diameter as well as wall thickness of pipeline enlarging, automatic welding becomes the main trend at the development of the pipeline welding technology in the foreseeable future. Grasping the mechanical properties of X80 pipeline girth weld is crucial to ensuring the safety of pipeline operation. In order to determine the mechanical properties of X80 pipeline girth weld welded by semi-automatic and automatic welding, the experimental specimens were extracted from X80 pipeline girth weld welded by semi-automatic and automatic welding respectively to carry out the uniaxial tensile tests, fracture toughness tests and Charpy impact tests. In the tensile tests, the ultimate tensile strength of X80 pipeline girth weld welded by automatic welding (GWA) was higher than that of X80 pipeline girth weld welded by semi-automatic welding (GWSA) and the former had smaller dispersions. The fracture toughness tests showed that the fracture toughness of GWA was higher than that of GWSA. The Charpy impact tests results revealed that the impact energy of GWA was higher than that of GWSA. From the overall point of view, the mechanical properties of GWA are better than that of GWSA. The automatic welding technique is recommended for the welding of X80 pipeline, which is vitally important to maintain the structural integrity of X80 pipeline.