A turret structure can be a major design driver for FPSO systems. Therefore, careful attention needs to be given to the estimation of extreme loads on this structural element.

This paper presents an all seas long-term analysis of the extreme global restoring forces acting on a FPSO turret structure, and a comparison with the results obtained through the contour line approach.

The analysis is performed in the time domain using a coupled model, where the floater is modelled in the software SIMO, and the risers and mooring lines are represented by a Finite Element Model in RIFLEX.

The characteristic responses of the turret structure with q-annual probability of exceedance are estimated from a full long-term analysis where both the short and long-term variability are considered. These results are compared to those obtained through the long-term estimate from the contour line approach when assuming 90th percentile for the worst sea state with q-annual probability of exceedance.

The results from the full long-term analysis will allow us to verify the adequate percentile level to be used with a contour line approach when estimating extreme turret structure loads.

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