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 C-F deterioration in FOWT structures and highlight the potential of condition-based maintenance.