| Abstract Scope |
Multi-pass butt joints for pressure-retaining equipment have traditionally been produced using conventional arc welding processes such as SMAW, GMAW, and GTAW. In contrast, handheld laser beam welding (HLBW) has so far been primarily associated with single-pass welding of thin sections. This perception limits the consideration of HLBW for thicker components typically found in pressure-service applications. However, recent work indicates that multi-pass HLBW can be used to weld thicker sections with unprecedented high impact properties in comparison to arc welding. This study presents a comprehensive assessment of multi-pass HLBW for pressure-service applications by combining laser beam characterization, mechanical testing, and microstructural characterization to provide insights to the strengthening mechanisms at play. The influence of key variables including power, beam angle, travel speed, spot size, and shielding gas is evaluated in relation to penetration mechanism, weld bead profile, and mechanical properties. The parameters examined are linked to ASME Sec. IX qualification requirements, which define essential and non-essential variables for laser beam welding (LBW) and low-power-density laser beam welding (LLBW). LBW encompasses both keyhole and conduction-mode welding, while LLBW is restricted to conduction mode. These defined penetration modes are not explicit to HLBW since the penetration mode can transition between keyhole and conduction modes depending on power, spot size, travel speed, and beam orientation. Practical concerns are also raised regarding the applicability of existing variables to a handheld process. The results aim to demonstrate the process, microstructure, and property relationships to support the identification of the essential and non-essential variables in HLBW. |