Microstructure and Mechanical Properties of X80 Girth Welds with Different Welding Processes

X80 pipeline steels were employed to investigate the effects of two different welding processes (swing welding and row welding) on the quality of weld joints. The welding thermal cycles of multi-pass welding were tested and the microstructures of the two kinds of weld joints were studied by optical microscope. The hardness tests as well as low-temperature impact tests combined with fracture analysis with scanning electron microscope (SEM) were carried out to evaluate the properties of weld joints. The results showed that under the similar condition of heat input, the grain of swing welding joint is bigger than that of row welding. The joint of row welding has lower hardness and better toughness, suggesting that the process of row welding can improve the properties of weld metal. Consequently, though swing welding is simple in operation and good in production efficiency, row welding is better in terms of microstructure and properties of weld joints.