From conventional to narrow groove repair: optimising repair welding with modern welding processes for high-strength offshore steels

Abstract The ongoing energy transition in Germany requires large offshore wind turbines with outputs over 10 MW and suitable deep-water subsea structures. This necessitates large towers made of high-strength steel with a yield strength of up to 500 MPa, placing high demands on manufacturers, especially regarding the welding of high-strength offshore steels. If weld defects are detected by non-destructive testing (NDT) during fabrication, repairs are recommended and typically performed by local gouging and rewelding. However, due to a lack of research, there are currently no adequate repair strategies or recommendations in guidelines and standards for thick sheets, particularly for high-strength offshore grades. This study, for the first time, compares optimised narrow gouging grooves and rewelding with controlled high-performance GMAW processes to conventional repair strategies. Thick plate joints and offshore steel grades with nominal strengths of 355 MPa to 460 MPa were investigated. Gouging was carried out using milling to ensure reproducibility. The restraint intensity of the repair groove, quantified numerically and experimentally, increases significantly for shorter groove lengths and thicker welds or plates. The weld-induced residual stresses caused or redistributed by welding, gouging, and rewelding were analysed by X-ray diffraction. Shorter groove lengths and wider opening angles result in a marked increase in residual stresses in the weld seam and adjacent areas. Nevertheless, the results show that average residual stress levels at the weld and a narrower, more consistent stress in the HAZ can be achieved through optimised repair strategies, even at higher restraint intensities. Adapting repair processes and boundary conditions may improve the utilisation of high-strength steel and support the safe, cost-effective construction of offshore structures for Germany’s energy transition.