Numerical analysis on the HSS and SIF of multi-planar DX-joint welds for offshore platforms

Among offshore platform structures, multi-planar tubular joints are usually in the most dangerous positions and generate fatigue cracks the earliest. In this study, DX-joints were regarded as the research object, and finite element method was adopted to conduct systematic research on the fatigue properties of multi-planar tubular joint welds. Axial, in-plane bending moment, and out-of-plane bending moment loads were applied to explore the stress distribution along the weld path and the hotspot location under different load conditions. Results indicated that the hotspot stress (HSS) location of DX-joints changed with the variation in the combined stress ratio. Through HSS analysis, cracks were prefabricated at the hotspot location of DX-joints to analyze the change rule of the stress intensity factor (SIF). The influence of different loads, crack lengths, and crack depths on SIF was studied to estimate the growth trend of the weld crack and its dominance. The findings can provide theoretical guidance for fatigue damage and safety assessment of offshore platforms.