A Comparison Between Air and In-Service Welding on Oxygen Concentration and Microinclusions in E7018-1 Weld Metal

In the maintenance of in-service pipelines, the use of covered electrodes is usual due to several factors such as the flexibility of welding in hard-to-reach places and its low cost. During in-service welding of pipelines, the line remains in operation, which implies more rigorous temperature gradients that can result in microstructures more susceptible to failure. The objective of this work is to relate the welding current and cooling conditions, commonly used in-service welding, with the oxygen content and the volumetric fraction of microinclusions. In this step, the effect on the oxygen content and the volumetric fraction of microinclusions are analyzed based on experimental results using the technique of factorial experiments. Bead-on-plate samples were welded under two cooling conditions, air and cooling with water, and two nominal welding currents, 86 A and 98 A. The increase in oxygen content was observed with increasing welding current and with the cooling rate. In addition, the higher cooling rate reduced the mean microinclusions size, which can suppress the formation of acicular ferrite and, consequently, reduce the toughness and the ultimate stress limit of weld metal.