TN X SN Fatigue Curves for KS Hook and Chain Using Finite Element Modelling

For mooring chains of offshore floating production units, API (American Petroleum Institute) recommends the use of its TxN fatigue curve considering the MBL (Minimum Breaking Load) of an ORQ (Oil Rig Quality) chain even if the chain has a higher grade. DNV (Det Norske Veritas) recommends the use of SxN fatigue curve where the stress is taken using the tension over the nominal area of the chain or wire rope. So it is easy to convert this SxN curve to a TxN curve or vice-versa. The geometry of the chain or wire rope and the material are implicit considered. To develop SxN curve for new accessories design it is necessary the using of FEM (Finite Elements Method) to obtain the distribution of stresses and strains and the stress concentration factor and the SxN curves of the material. The analysis of the tension and the stress concentration factor will be used to obtain the slope and intercept parameters of the fatigue curve. This paper will present the study developed for KS hook and how to obtain the fatigue curve for this accessory based on published papers, rules and recent tests.