Recommended Hot-Spot Analysis Procedure for Structural Details of Ships and FPSOs Based on Round-Robin FE Analyses
As part of the Joint Industry Project FPSO Fatigue and Fracture Capacity, a Special Task Group of 9 participants performed investigations regarding finite element (FE) modelling and analysis of typical structural details in FPSOs (Floating Production, Storage and Offloading Units) as well as in ships. The purpose of this special effort was to develop recommendations on appropriate hot-spot stress methods and S-N data for fatigue strength design. In total, 5 details with different characteristics, from the perspectives of both geometry and fatigue loading, were selected, for which stress measurements and fatigue tests are available. Participants developed various FE models, using different types and sizes of elements, modellingand tress evaluation techniques as well as FE programs. Comparisons between the analysis results and measured stresses near the weld toes allow conclusions to be drawn. Three different stress extrapolation techniques for predicting hot-spot stresses at the weld toes were investigated. The resulting hot-spot stresses, together with the estimated fatigue lives, are compared against the existing design S-N curves published by the International Institute of Welding (IIW). It was concluded that the hot-spot stresses predicted usingthe 3 stress extrapolation techniques, where in most cases the element sizes and stress evaluation points are determined by the plate thickness, can be used with the current design S-N curves. One of the recommended methods requires no stress extrapolation, which is considered an attractive and practical alternative to the existingpractices developed by classification societies
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