New welding procedures and applications are often developed in order to attend the increasing demand of productivity and quality, keeping lower costs. During the pipelines assembly, slower low-energy welding procedures might be used due the position limitation, which can vary between flat and overhead position, but whenever is possible on and off shore, high-energy welding procedures are chosen. Submerged arc welding (SAW) is widely used in such applications due its high heat input, still it has limitations, mostly by bevel preparation. Laser-MIG hybrid welding on the other hand has a great performance on higher wall thicknesses welding, although the initial investments are strictly high. The Plasma-MIG hybrid welding has appeared as an intermediate alternative for these procedures, having lower investments compared to laser hybrid procedures, and better performance compared to individual wire arc procedures. It consists in two arcs acting on the same welding pool, while the plasma arc starts the melting and initiates the keyhole, the MIG arc goes right after consolidating the penetration and bridging space between the plates to be welded. Therefore, experimental tests were carried out in 12mm AISI 1020 carbon steel plates laid out at 1G position, to develop initial groove necessary and welding parameters. After the initial parameters for this condition were found, it was applied in the circumferential single pass welding of API X-70 pipe under two different backing materials. The electrical parameters were monitored online welding, which allowed identifying great electrical stability during weld, the welding bead was continuous during weld and macrographs analysis showed no signs of discontinuities, porosity or lack of fusion.
Keywords: Plasma-MIG; weld bead; penetration; speed; keyhole.
ZANINI. J.B.; SILVA. R. H. G.; NOGUEIRA. R. R.; FAGUNDES. R.F. A Hybrid Plasma-MIG Welding Solution to Improve Productivity in Pipelines Construction. Brazilian Petroleum, Gas and Biofuels Institute - IBP. Rio Pipeline Conference & Exhibition, Rio de Janeiro, 2019.