Development of High Current MIG+2SAW Technique for Heavy Wall UOE Linepipes

Abstract

MIG+2SAW technique has been developed for longitudinal welding process to produce the heavy wall UOE linepipes up to 50 mm in thickness.
(1) An experimented MIG+2SAW equipment is designed so that the leading electrode is DCRP for high current MIG welding and the middle and trailing electrodes are connected in Scott transformer connection for 2SAW. This equipment placing MIG and 2SAW torches on one cart can weld test plates with one-run. The arc interaction between MIG and 2SAW has hardly been observed.
(2) MIG+2SAW process is devised to disperse the heat input to decrease it per one molten pool as compared with 3SAW because a torch spacing between MIG and 2SAW is long enough and two molten pools are formed. Therefore weld metal and HAZ in the center of plate thickness by MIG+2SAW process give a better toughness than those by 3SAW.
(3) As the heat input of 2SAW on MIG+2SAW process can be lowered as compared with that of 3SAW, MIG+2SAW process consumes a fewer fluxes than 3SAW. The shielding effect of the molten slag is scarcely deteriorated because it is not overheated even if the fused flux is used. As a result the weld bead in 50 mm thickness plate is sound and slippery.