Stress intensity factors for axial semi-elliptical surface cracks and embedded elliptical cracks at longitudinal butt welded joints of steel-lined pressure tunnels and shafts considering weld shape

When for steel liners of pressure tunnels and shafts high-strength steels are used, welded joints are subject to the risk of hydrogen induced cold-cracking in the base material. Longitudinal butt welded joints are critical regions as they are loaded transversely. For an accurate engineering fatigue and fracture assessment, solutions for stress intensity factors (SIF) are required, considering the weld shape and the global behavior of the liner (i.e., geometrical imperfections and interaction with surrounding concrete and rock). In this study, SIF for axial semi-elliptical surface cracks and embedded elliptical cracks at longitudinal butt welded joints of steel liners are studied by means of the finite element method. At first the applicability of published parametric equations for SIF of elliptical cracks in plates is validated. Then the influence of the weld shape is assessed through a systematic parametric study. It is shown that the weld profile has a significant influence on SIF for semi-elliptical surface cracks while it has no significant influence on SIF for embedded elliptical cracks within the studied range of relative crack depth. Finally, a new parametric equation is proposed to estimate the weld shape correction factor for semi-elliptical surface cracks.