Influence of pores on the fatigue life of welded joints and investigation of acceptance criteria defined in standard documents

Inner defects in welded joints constitute concurrent sites for fatigue failure in welds, especially when high fatigue resistance is enforced at weld toe and root. Existing standards limit the size of pores and other inner defects proportional to the sheet or weld thickness, but for larger dimensions cutoff values are in place. This leads to overly high acceptance criteria when it comes to thicker sheets, as e.g. used for wind turbine towers. To analyze the influence of pores on the fatigue life, specimens with targeted pore sizes larger than the usually accepted were tested under fatigue loading. In the present study a numerical model for fatigue assessment was developed based on the experimental results, which allowed to further vary pore sizes and locations. It is shown, that for larger weldments the acceptable pore size can be increased without large reductions in fatigue life. But, the location of the pore with regard to the specimens surface has shown to have a large influence – an effect that is currently not considered in common weld quality documents. IIW Document No.: XIII-2994-2023