Study on the Influence of Different Welding Processes on the Mechanical Properties of X80 Girth Welding Joints

Abstract The emergence of welding defects and uneven distribution of mechanical properties will easily make the welded joint a weak part of the pipe structure. It is prone to failure when further subject to complex loads. Therefore, optimization of the welding process and design of the strength and toughness properties of the welded joints are important means to ensure the safety and smooth operation of the pipeline. To this end, five X80 steel girth welding joints with different welding processes were manufactured in this study. Then, through the hardness test, small punch test and three-point bending test, the distribution laws of the hardness, strength, and fracture toughness of the five different girth welding joints were determined, respectively. On this basis, the main control factors on the mechanical properties in the welding process parameters were identified. Among them, automatic welding method made the weld zone having high strength properties, but poor fracture toughness compared with the semi-automatic method. In the automatic welding process design, attention should be paid to avoid the use of excessive strength of the welding material to ensure its toughness properties. When reducing the welding speed in semi-automatic welding process and making the welding heat input significant increased, the strength properties of the heat-affected zone and weld zone decreased, meanwhile the fracture toughness of the weld zone decreased significantly. In the semi-automatic welding process design, the welding current and speed parameters should be strictly controlled to ensure the mechanical properties of the welded joint.