Risk-Based Inspection Planning for Mooring Chain

Abstract

The use of risk-based inspection planning for offshore structural components is becoming quite familiar. This paper describes an application of this technique to mooring chain. In many cases, the technique is based on probabilistic modelling of fatigue crack growth in the structural components, and updating of the failure probability on the basis of inspections. The extension of this basis from a single component to very many components is necessary to tackle series systems, such as mooring chain, where a fatigue fracture can arise in any chain link. The theoretical basis for the analysis is described, including details of the model for stochastic dependency between the chain links. Results are shown that compare failure probabilities for a single chain link and a chain segment. The effects of various levels of inspection coverage are illustrated. An example of a cost optimal inspection plan is developed for mooring chain on an FPSO in the northern North Sea.