Abstract The structural integrity of welded steel components depends on the quality of the welding process. Internal imperfections such as porosity and lack of penetration are unavoidable in practical fabrication. Although design standards assume defect-free connections, such imperfections may reduce load-bearing capacity and affect structural safety. This study investigates the influence of internal weld defects on the static performance of butt-welded steel connections. A comprehensive experimental program was conducted on large-scale tensile specimens with intentionally introduced internal imperfections. Lack of penetration and porosity. Material properties were characterized by tensile, Charpy impact, and hardness tests. Non-destructive testing using ultrasonic testing with the total focusing method (TFM) was performed to quantify defect size and distribution. Quasi-static tensile tests were subsequently carried out at room temperature and − 30 °C to evaluate the influence of defect characteristics on load-bearing and deformation behavior. The results show that lack of penetration reduces the ultimate load-bearing capacity, particularly for one-sided root gaps due to eccentric stress states, although the reduction is smaller than predicted by cross-sectional area loss alone. Porosity exhibited a differentiated effect: isolated pores had little influence, whereas clustered porosity altered failure modes and reduced ductility, especially at low temperatures. For both defect types, elastic stiffness and the onset of strain hardening were largely unaffected. Overall, internal weld imperfections affect static resistance less severely than EN ISO 5817 suggests, implying conservative acceptance criteria. These conclusions are limited to quasi-static tensile loading and do not extend to fatigue, fracture mechanics, or multiaxial conditions.
Voelkel et al. (Sat,) studied this question.