Service life of unbonded flexible risers in offshore operations may be limited by designs based on conservative corrosion fatigue S-N curves. A new corrosion fatigue test methodology simulates the steady-state annulus environment of long-operated pipes with realistic carbon dioxide (CO2) and hydrogen sulfide (H2S) partial pressures, supersaturation of dissolved corrosion products, protective iron carbonate (FeCO3) film on carbon steel armor wire surfaces, and corrosion rates around 0.01 mm/y. This yields more accurate S-N curves (stress vs. number of cycles to failure) tailored to field conditions, enabling riser lifetime extensions. The service life of six risers was extended beyond original design life without compromising safety. This methodology improves fatigue life predictions and supports optimized riser management.
Berntsen et al. (Tue,) studied this question.
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