Evaluation of Stainless Steels Welds Produced by Gas Tungsten Arc Welding With High Silicon Containing Solid Welding Filler Rod to Omit Back Shielding

Where single-sided welding is applied to fabrication and erection of piping made of low alloy steels, stainless steels (SS) and nonferrous alloys, back shielding by inert gas and its maintenance for the first few layers is required to obtain good weldability and to prevent oxidation of welds. In order to save consumption of inert gas, isolations to make a chamber for inert gas purging are placed inside piping for the joint and the adjacent areas to be welded, instead of inert gas purging for the whole piping length. However, placing the isolations before welding and removal of them after welding are sometimes impractical due to piping layout and construction sequence such as closure joints. To solve this issue, practices for omission of back shielding, such as use of flux cored welding filler rods for gas tungsten arc welding (GTAW) or high silicon welding wires for gas metal arc welding in modified wave short circuit mode (GMAW-S), had been developed and achieved the objective. These practices, however, require special training and qualifications for welders, close dimensional tolerance for fit-up, and special welding power source equipped with electrical waveform control. Also, welding quality such as remaining slag or spatters on piping internal is sometimes an issue. To make up for these shortcomings, high silicon solid welding filler rod was introduced to stainless steel welding by GTAW to eliminate back shielding, and mock-up tests were conducted. The properties of the welds were studied by comparison to the welds produced by the other welding processes such as GTAW with back shielding, GTAW with flux cored filler rod without back shielding, and GMAW-S using high silicon solid wire without back shielding. This paper discusses and evaluates the potential of the GTAW with high silicon solid filler rod which can eliminate the inert gas back shielding.