Probabilistic vulnerability assessment of floating offshore wind turbines under typhoon hazards considering long-term corrosion–fatigue degradation

Floating offshore wind turbines (FOWTs) are increasingly exposed to tropical cyclone (TC) hazards, which impose severe cyclic and transient loads on structural components. The complex marine environment leads to continuous corrosion-fatigue (CF) deterioration, gradually weakening the typhoon resistance and increasing system fragility over time. This study proposes a probabilistic framework for evaluating the reliability and vulnerability of FOWT flange bolted connections under typhoon conditions while accounting for CF-induced degradation. The framework integrates long-term environmental characterization, TC-induced wind-wave field modeling, a probabilistic CF model, and structural dynamic analysis. It is applied to assess the vulnerability and risk of a semi-submersible wind turbine. The results indicate that CF degradation leads to a reduction of flange-connection bending and axial resistances to approximately 20% and 40%, respectively. The system reliability declines rapidly under the combined effects of CF and typhoon loading, with flange connections exhibiting pronounced susceptibility to coupled cyclic and transient extremes. Moreover, the failure-probability distribution progressively shifts toward lower load levels with increasing deterioration, indicating that typhoon-induced stress amplification markedly reduces the structural safety. The cumulative system risk rises monotonically throughout service life, emphasizing the importance of accounting for long-term CF deterioration in resilience-oriented maintenance strategies for FOWTs operating in typhoon-prone regions. • Developed a probabilistic framework for FOWT typhoon–CF vulnerability. • Integrated wind–wave modeling with corrosion–fatigue crack evolution. • Coupled resistance degradation with dynamic typhoon response analysis. • Applied multi-mode reliability and risk assessment for flange connections.