Influence of post-weld improvement on fatigue strength of butt-weld in different steel grades

Abstract The IIW recommendations for Fatigue Design of Welded Joints and Components published in 2024 define four fatigue classes for butt welds that are welded from two-sides (details 211, 212, and 213) depending on the misalignment quality, the weld bead geometry and whether the weld is ground flush. As with other finishing techniques (HFMI, TIG dressing) where the steel grade is considered, flush grinding could allow for taking advantage of improved fatigue properties. In this study, fatigue tests were conducted with S355, S460 and S690 butt-welds with misalignments of 5% (Case 212) and 10% (Case 213), as well as with toe grinding (Class B125 of ISO 5817) and flush grinding (Case 211) to assess the effect of the quality improvement on the fatigue strength. In the as-welded condition, reducing the misalignment to 5% does not necessarily lead to a significant improvement in fatigue performance compared to larger misalignments as the quality of the weld toe is a primary factor in the fatigue strength. The B125 quality can easily be achieved by grinding the weld toe, resulting in a local transition radius well above 4 mm. As expected, flush grinding greatly improves the fatigue life of the welds, exceeding that of case 211 (FAT125, m = 5). Moreover, this improvement is sensitive to the grade of the base material as are other finishing techniques.