Coupling multi-physics models to corrosion fatigue prognosis of high-strength bolts in floating offshore wind turbine towers

Floating wind offshore turbines (FOWTs) tap into the immense Aeolian resource in deep-water oceans. The turbine structure, especially in ring-flange (RF) connections, are highly prone to corrosion fatigue (C-F) deterioration due to the combination of strong wind-wave loads, structural flexibility, and high corrosivity. This study provides innovative insights into the C-F deterioration of FOWT towers by integrating site-specific data, material test results, multi-physics simulations, and deterioration models. A probabilistic C-F (PCF) evolution model is tailored for bolts in RF connections, accounting for multiple failure modes. Concurrently, the corrosion test data are adopted to estimate the corrosion rate from the site-specific ambient conditions, including the temperature, humidity and airborne salinity. The result indicates a strong correlation between wind-wave spatial distribution and C-F damage, for which the critical bolt aligns with high-velocity winds. Meanwhile, the bolt deterioration is accelerated under high corrosivity, risking premature failures. Moreover, compared with the traditional fixed-bottom foundation, the floating platform amplifies the tower dynamics in both mean value and variation, which in turns escalate stress ranges in bolts. The findings underscore the importance of monitoring CF deterioration in FOWT structures and highlight the potential of condition-based maintenance.