Agrowaste‐Derived Biomaterials for Sustainable Underwater Welding Electrodes: A Review

Underwater welding is essential for marine infrastructure maintenance, but wet‐arc processes suffer severe weld defects due to water vapor dissociation and high hydrogen levels in the weld pool. Conventional electrodes (rutiles, basic fluxes) still generate high diffusible hydrogen and hard HAZs, limiting weld quality. As a sustainable alternative, this review examines agrowaste‐derived biomaterials (rice husk, bagasse, coconut shell, corn stover, banana peel, etc.) as flux and coating components for underwater welding electrodes. We compare the feedstock chemistry (lignocellulose, ash/minerals) of each biomass, the conversion processes (pyrolysis, activation, pelletizing, sintering, binder selection), and electrode formulations proposed in recent studies. The review summarizes welding performance data (mechanical strength, hardness, H₂ content, porosity) for bio‐flux electrodes versus conventional fluxes. It also analyzes arc stability and metallurgical effects: how carbonaceous slag and K/Ca silicates from biomass influence the arc and mitigate hydrogen ingress. Environmental and economic impacts are assessed through preliminary life‐cycle analysis, highlighting carbon footprint reductions and cost savings from using waste biomass. Finally, we identify critical research gaps in welding metallurgy such as hydrogen entrapment, slag-metal reactions, material processing (scale‐up of biochar electrodes), and regulatory issues. This review provides a comprehensive roadmap for developing sustainable underwater welding electrodes from agrowaste, to maintain weld quality while reducing environmental impact.