A global-to-local framework for corrosion-fatigue reliability assessment of deepwater top-tensioned risers

Deepwater top tensioned risers (TTRs) experience nonlinear, uncertain fatigue degradation under combined environmental loading, platform motions, and marine corrosion. This study develops a reliability framework integrating global dynamic analysis, local corrosion-fatigue simulation, and Monte Carlo analysis. A full-scale time-domain finite element model, validated against published experiments, provides stress responses across sea states. Loads at the fatigue-critical section are transferred to a local model, where continuum damage mechanics and a Python–Abaqus iterative procedure calculate damage accumulation. An equivalent damage parameter is modeled probabilistically to evaluate fatigue-life distributions and time-dependent reliability across four corrosion states. Results identify the splash zone as the critical region because of high mean and alternating stresses. Severe sea states, stronger corrosion-fatigue coupling, and greater initial damage accelerate degradation, while increasing corrosion severity shortens fatigue life and advances reliability decay. The method links global response, local damage, and uncertainty for deepwater TTR reliability assessment.