Assessment of Conventional and Controlled Short-Circuit GMAW Processes for Steel-Pipe Welding in Single Pass

The development of power sources towards the GMAW derivative processes with short-circuit metal transfer (also known as controlled short-circuit) has become a trend in the search for high productivity and high quality weldments, especially for pipe welding. It is believed that the control of current achieved in such processes improves the metal transfer, reaching stability on both process and weld pool. Therefore, this work aims to establish operational envelopes and also both advantages and limitations of GMAW processes with conventional short-circuit transfer and derivatives (STT, RMD and CMT) for pipe welding. The weldments were carried out in thin-wall carbon-steel pipes with nominal diameter of 2 ½’’ using single pass and both upward and downward progressions. The parameter sets for each process were varied together with wire-feed speed, keeping the same amount of deposited material, enough to fill up the joint in a single-pass bead. The results show that the conventional short-circuit GMAW process presents a suitable operational envelope for both progressions, whereas STT and RMD processes present a larger envelope for downward progression. On the other side, CMT process has a more robust envelope for upward progression and works with lower voltages and, therefore, lower heat input.