Probabilistic corrosion-fatigue framework for structural steels

Offshore wind turbines (OWTs) are subjected to severe corrosion-fatigue (C-F) deterioration. The use of uncoated High-Performance Weathering (HPS-W) steel has been proposed to reduce lifecycle costs, but its performance in chloride-rich marine environments is contentious and lacks quantitative assessment, creating a significant knowledge gap. This study develops a high-fidelity probabilistic corrosion-fatigue (PCF) model to address this gap. The model integrates a three-stage evolution mechanism with stochastic multi-site cracking and coalescence. The framework is validated against experimental data for both in-air and coupled C-F conditions before being applied to a case study on a critical OWT butt-welded steel joint to assess the performance of HPS-W steel against conventional carbon steel (CS) in unprotected conditions. For a baseline C4 marine environment, the HPS-W weld showed a 2.8-fold increase in design service life over CS. However, the performance is highly sensitive to operational parameters; the design life decreases by a factor of six within the OWT operational frequency range (0.1 to 0.5 Hz) and by 3.7 times when moving from a C4 to a C5 marine environment. The results are synthesized into frequency-variant probabilistic S-N (f-P-S-N) surfaces, providing a comprehensive tool for the reliability assessment of this contentious material choice in offshore applications.