A Study on Gap Bridging Formation Conditions in Butt Root Pass Welding Using GTAW

Abstract

GTA welding is a representative welding technique applied to root pass welding of piping. The pipe root pass welding significantly influences the determination of welding parameters owing to the root gap and step change occurring during installation. GTA welding has the advantage of being able to control current (A) and wire feeding speed (WFS) as independent variables; however, determining these variables is difficult. In this study, the change in the back bead height (Bbh) was observed by changing the root gap and WFS while the welding speed and welding current (A) were fixed. By fixing the welding speed and changing the welding current (A), root gap, and WFS, the gap bridging possible condition was expressed as a region. When the root gap changed from 0~1 mm and from 1~2 mm, the back bead height was greater than or equal to 0 mm. Possible welding current and WFS and the setting range of the welding heat input ratio (HIR) were presented.