Fatigue strength evaluation of flush-ground butt welded S355 girth welds in close proximity

Abstract

The fatigue performance of welded tubular structures is a critical consideration in offshore and structural steel applications subjected to cyclic loading. While flush-ground one-sided butt welds are known to improve fatigue life, current design standards primarily provide guidance for isolated welds and do not address the effect of closely spaced welds. In practice, multiple welds may occur in close proximity due to repair operations or fabrication constraints, potentially altering fatigue behavior through residual stress interactions and heat-affected zone overlap. This study investigates the fatigue behavior of flush-ground, one-sided butt welds fabricated on tubular specimens with weld spacings of 5-, 10-, and 15-mm. Small-scale specimens are employed to systematically evaluate the effect of proximity on fatigue performance, and S–N curves are developed for each spacing under cyclic tensile loading. Experimental results are used to quantify the influence of weld proximity on fatigue life, crack initiation, and propagation, providing insights into the interaction between flush-ground treatment and weld spacing. The findings fill a critical gap in fatigue assessment of tubular structures, offering practical guidance for designers and fabricators and informing potential updates to design codes. The study demonstrates that weld proximity can markedly affect fatigue performance, even in flush-ground welds, and highlights the importance of considering these effects in the design and structural integrity assessment of space-constrained welds in onshore and offshore tubular structures.