ECLIPSE: Collaborative Research: Advancing Subsea Welding through Foundational Investigations of Plasma-Liquid-Solid Interactions

Reliable underwater welding is essential for maintaining offshore energy systems, naval ships, bridges, pipelines, ports, and emerging subsea robotic infrastructure. However, welding underwater is extremely challenging because surrounding water cools the metal quickly and introduces gases that can weaken the weld. As a result, underwater welds can crack or fail over time, creating safety and reliability concerns. This ECosystem for Leading Innovation in Plasma Science and Engineering (ECLIPSE) award addresses this national need by developing the scientific foundation for a new plasma-assisted underwater welding process capable of producing stronger, safer, and more durable joints in marine environments. The award studies how controlled plasma arcs can create a small, stable protective region around the weld pool, reducing rapid cooling and limiting hydrogen entry into the metal. By enabling high-integrity repair and construction directly underwater, the award is expected to advance US capabilities in offshore energy resilience, naval readiness, marine transportation, and subsea manufacturing. The award also contributes to workforce development by training students at the intersection of plasma science and advanced manufacturing, while advancing knowledge that can support future standards and technologies for underwater repair. This award aims to establish the plasma-surface interaction science needed to enable high-quality underwater welding under high-pressure marine conditions. The central hypothesis is that a precisely controlled plasma arc can generate and sustain a localized vapor cavity around the molten weld pool, thereby reducing convective heat loss, stabilizing arc energy transfer, and suppressing hydrogen diffusion that leads to porosity, embrittlement, and cracking. The research will investigate how hydrostatic pressure and water chemistry, especially salinity, influence electron temperature, ion density, arc thermodynamic equilibrium, arc stability, vapor cavity dynamics, and heat transfer efficiency to steel and aluminum alloy workpieces. The team will combine controlled underwater plasma arc experiments, in situ plasma diagnostics, high-speed imaging of arc-weld pool interactions, thermal monitoring, weld pool solidification analysis, and post-process characterization of microstructure, porosity, hardness, residual cracking, and hydrogen-related defects. Experimental results will be used to validate process-structure-property relationships that connect underwater plasma behavior to weld quality and defect formation. The expected outcome is a scientifically validated plasma-assisted underwater welding framework that bridges fundamental plasma physics, transport phenomena, and advanced manufacturing, enabling robust underwater joining processes for marine infrastructure, offshore energy systems, naval applications, and subsea robotic repair. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.