A defect-aware fatigue life framework for corroded mooring chains integrating cyclic plasticity and crack growth

Current design approaches for offshore mooring chains primarily rely on simplified corrosion allowances that may fail to capture the severe fatigue degradation caused by very localised pitting and preferential weld corrosion (PWC). This paper presents a novel, defect-aware fatigue assessment framework that integrates finite element analysis, cyclic plasticity, and fracture mechanics to deliver high-fidelity life predictions for the experimentally tested corroded chains. The methodology explicitly models pitting at the crown and trench-like PWC grooves at the weld-line as geometric stress concentrators. A mechanics-based algorithm, combining strain-life initiation and Paris-law propagation, is applied using local stress–strain fields from dedicated FE models. The framework is validated against a harmonised dataset of full-scale S-N tests from new and corroded Grade R4 chains. Results demonstrate that the critical failure location shifts to the crown under pitting corrosion, and the model accurately predicts the associated life reduction, which may be significantly under-estimated by the current simplified methods. In particular, the predicted fatigue strength for corroded chains was up to a factor of two lower than that suggested by the DNV design curve, highlighting the importance of defect-aware modelling in safety-critical design. This work provides a robust, physics-based tool for the integrity management of critical offshore assets, moving beyond empirical S-N curves. • A novel defect-aware framework for fatigue life prediction of corroded mooring chains. • Explicit modelling of pitting and weld corrosion as geometric stress concentrators. • Integration of cyclic plasticity with a short/long crack growth methodology. • Comparison with full-scale S-N data, showing up to 2×lower strength than DNV.