Localized Purging Methodology to Minimize Oxidation During Gas Tungsten Arc Welding of 304L Stainless Steel Pipes

In reprocessing plant with high-density piping, inert gas purging for gas tungsten arc welding (GTAW) of 304L stainless steel pipes to minimize oxidation is difficult at some places due to complexity of design and access limitations. One typical example is terminal joints. During GTAW of the terminal joints, oxidation due to inadequate purging is observed, apart from weld defects. Since the pipe joints are not amenable for inspection after commissioning, it is essential to ensure integrity of each pipe joint weld by stringent quality assurance measures and volumetric nondestructive testing such as radiographic testing. Oxidation of any magnitude and any linear defect indications at root are not acceptable as they promote corrosion at the root side of the pipe welds during service. Conventional full volume flow purging is time-consuming and expensive depending on the volume of the processing tank. Other well-established localized purging methods such as water-soluble dams and thermally disposable barriers are not feasible for most of the terminal joints. This paper presents development and implementation of an alternate localized purging methodology that uses a perforated copper flask to address oxidation and associated weld defect formation during the welding of SS 304L pipe terminal joints. This methodology is found to be faster and cost-effective than the conventional full volume flow purging methodology.