Results from full scale fatigue tests of offshore mooring chains performed in recent years have revealed considerable influence of respectively mean load and corrosion condition on the fatigue capacity. It has been shown that a reduction of the mean load gives an increase in fatigue life, whereas the corrosion experienced by retrieved chains have significant negative impact. Neither of these effects are properly addressed by current&nbsp;S-N design curves or&nbsp;design practice.This paper suggests an extended S-N curve formulation, that includes the effects of mean load and corrosion condition. The parameters of the extended formulation are estimated empirically from mooring chain test data that includes new and used chains, with various mean loads and with different degrees of corrosion. It is shown that the fitted curve&nbsp;agrees well with existing curves and previous studies on mean load, when compared for similar mean load and corrosion values.&nbsp;The fitted capacity model is then used for fatigue damage calculation for the mooring system of a typical production semi-submersible, to provide an example of the practical impact of realistic mean loads and mooring chain corrosion. These results demonstrate the importance of taking both effects into consideration to avoid an&nbsp;overly conservative or non-conservative fatigue assessment.

Fatigue Assessment of Mooring Chain Considering the Effects Of Mean Load and Corrosion

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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