Evaluation of Welds Produced by No Backing Gas - Gas Tungsten Arc Welding With High Silicon Contained Type 347 Stainless Steels Solid Filler Rod

Abstract For fabrication and erection of piping made of low-alloy steels, stainless steels (SS) and nonferrous alloys, single sided welding from external side is standard practice due to limited accessibility of welding from internal side. Therefore, back shielding and maintenance by inert gas (e.g., argon (Ar), nitrogen (N2), and mixed Ar/N2 for the first few weld layers is usually required. Back shielding provides good weldability due to fluidity of molten metal, and prevents oxidation of weld metal and heat affected zone (HAZ) which may cause deterioration of corrosion resistance and mechanical properties of welds. In order to reduce consumption of inert gas for back shielding, physical isolation dams are placed inside piping adjacent areas to the joint to make a chamber for inert gas purging, instead of inert gas purging for the whole piping length. However, placing of purge dams before welding and removing them after welding is sometimes impractical due to piping layout and construction sequence (e.g., closure joints). To solve this issue, welding procedures that eliminate back shielding (e.g., flux cored welding filler rods for gas tungsten arc welding (GTAW) or high silicon contained welding wires for gas metal arc welding in short circuit mode (GMAW-S)) have been developed to achieve the same objective. These practices require special training and qualifications for welders, closely dimensional tolerance for fit-up, and special welding power sources. Also, welding quality (e.g., remaining slag or spatters) is sometimes an issue. These shortcomings cause hesitation in applying backing gasless welding procedures. To make up for these shortcomings, high silicon containing solid welding filler rod have been developed for austenitic SS Type 304L and 316L [1], and Cr-Mo steel Grades P5 [2] and P9 [3] allowing welding with no backing gas (NBG) GTAW. Mockup tests have been conducted, and mechanical properties of the welds has been studied; comparing them to the welds produced by the other welding processes (e.g., GTAW using solid filler rod with back shielding (conventional procedure) and GTAW with flux cored filler rod without back shielding). Consequently, NBG GTAW has been implemented to piping fabrication and erection for Type 304L in oil and gas industries since 2023[4]. To expand the application range of NBG GTAW in oil & gas industries, high silicon containing Type 347 filler rod for GTAW was used, and the properties of welds by NBG GTAW have been studied, comparing them to welds produced by other welding processes. This paper discusses and evaluates the potential of NBG GTAW for stabilized SS applications.