Alternate Approach for Reduction of Lack of Fusion Defect During Onsite Welding of Small Bore AISI 304L Pipe Welds of Nuclear Facility

Austenitic stainless steel AISI 304L small bore pipes are widely used in nuclear facilities for transferring radioactive fluids. However, Lack of fusion (LF) weld defect during Gas Tungsten Arc Welding (GTAW) of on-plot small bore pipe welds remain a challenge due to site constraints, predominantly in 2G and 5G welding positions at higher elevation. A hybrid welding approach combining Activated TIG (A-TIG) for the root and conventional GTAW for cover pass (A-GTAW) was developed to address inaccessibility and eliminate edge preparation. Procedure qualification, intergranular corrosion testing, Stress corrosion cracking (SCC) evaluation and microstructural studies confirm the viability of A-GTAW. Procedure qualification showed tensile strength up to 546 MPa, micro-hardness up to 204 VHN and delta ferrite ~ 6.5 FN. A-GTAW welds exhibited full fusion, refined grain structure and narrower HAZ. Intergranular corrosion rates (1.5–1.9 mpy) and Stress corrosion cracking (SCC) tests confirmed better corrosion resistance versus conventional GTAW. Results show improved weld integrity and productivity under site-simulated conditions, demonstrating its reliability and suitability for field applications in nuclear piping systems.