Efficient Welding of 80 mm S355ML Plates Using a Hybrid Laser-Arc and Narrow-Gap SAW Process

A new welding approach combining hybrid laser-arc welding (HLAW) and narrow-gap submerged arc welding (SAW) was investigated for joining 80 mm thick S355ML steel plates used in offshore wind turbine structures. The U-shaped joint preparation consisted of a 40 mm root face welded by HLAW, followed by a 23 mm narrow-gap section completed with multi-layer SAW passes. Process efficiency and mechanical performance were evaluated in comparison with conventional multi-pass SAW. The results showed that the combined process significantly reduces weld volume, filler metal consumption and heat input while maintaining the strength and toughness required for offshore applications. Mechanical testing confirmed a sound joint with a favorable and uniform hardness profile and adequate low-temperature performance. Charpy V-notch tests at -40 °C yielded average absorbed energies of 138 ± 45 J in the arc-dominated region and 65 ± 12 J in the laser-dominated region of the hybrid weld. The proposed approach provides an efficient and technically feasible solution for the fabrication of thick-walled offshore structures.