Experiences show that mooring line failures have occurred due to crack propagation in chain links. Moreover, the crack propagation is accelerated by corrosion. To maintain the safety of floating structures in a long-term period of, say 20–30 years, it is therefore crucial that these chain links are properly designed as well as inspected and repaired during operation. The aim of this paper is to establish a reliability-based formulation for assessing mooring chains under the deterioration due to combined fatigue cracking and corrosion wastage. The crack growth in chain links has been modelled using the 2-dimensional Paris-Erdogan equation, which is validated by comparison with the SN data on a reliability basis. The corrosion is treated by considering the diameter reduction and the fatigue crack growth rate, using three zones of corrosion, namely the splash, catenary and bottom zones. A fatigue reliability case study of studless chain links is carried out considering various system models and proper correlation between links. The material correlation is modelled by splitting variables for the global and local effect. Accumulated failure probabilities of one year up to twenty years have been calculated to illustrate the effect of corrosion on fatigue reliability. A sensitivity study has been carried out on the initial crack size, the crack aspect ratio and the material correlation between links, when applying the fracture mechanics approach. Based on the case study, it has been found that the splash zone has an important effect on the failure probability of the entire mooring line, especially under corrosion of long time.

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