Description:
Pipe girth welds are prone to incomplete fusion problems in the automatic welding process of long-distance pipelines, which is often related to temperature inhomogeneity in the weld bead. The narrow gap and micro-swing welding technique was applied in pipeline construction to improve welding quality. The manuscript provides a detailed investigation of the micro-swing welding technique with a combination of welding experiments and numerical simulation. A swing welding strategy was proposed according to the actual welding condition in pipeline construction to study the formation mechanism of weld joints. The swing width grew to 1.25–1.35 times from the 3 to 6 o’clock position in the same filling layer. It also increased with filling layers, and filling layer 5 had the biggest swing width, almost two times that of filling layer 2. “Middle concave” morphology appeared at the 3 o’clock position, which could effectively avoid the occurrence of incomplete fusion, while “hump” morphology may appear at the 6 o’clock position, and incomplete fusion defects occurred if the next pass failed to eliminate the influence of the “hump”. The temperature field presented an obvious “sawtooth” shape at small swing frequencies, which could cause temperature inhomogeneity. It could be effectively eliminated when swing frequency reached over 5 Hz.