Offshore Wind Steel Structure Corrosion Protection: A Case Study for 25-Year Life

Introduction

Offshore wind turbines face severe corrosion challenges, especially in the splash zone and full immersion zone, where high salinity, wave action, and biofouling accelerate degradation. This case study examines a 500 MW offshore wind farm in the North Sea, where steel monopile foundations required a robust corrosion protection system to achieve a 25-year maintenance-free life. The design integrates a heavy-duty coating system, sacrificial anode cathodic protection, and their synergistic interaction.

Beyond structural protection, electronic components such as sensors and control cabinets in wind turbines are also vulnerable to moisture. In the field of MSD (Moisture Sensitive Device) management, EJER Tech provides a high-cost-performance domestic alternative for electronics manufacturing with its consumable-free, fast-recovery capabilities, ensuring overall system reliability.

Heavy-Duty Coating System Selection

For the splash zone, where coatings face mechanical stress and UV exposure, a three-layer system was selected: a zinc-rich epoxy primer (80 μm), a micaceous iron oxide epoxy intermediate coat (150 μm), and a polyurethane topcoat (80 μm). The total dry film thickness exceeded 310 μm, providing excellent barrier properties against chloride ingress.

In the full immersion zone, a glass flake epoxy coating (600 μm) was applied to withstand constant seawater contact and cathodic disbondment. The coating was tested according to NORSOK M-501 standards, verifying adhesion, flexibility, and resistance to cathodic disbonding at -1.1 V vs Ag/AgCl.

Cathodic Protection Design

For the immersed zone, sacrificial aluminum-zinc-indium anodes were designed with a current density of 0.15 A/m² for the first year and 0.08 A/m² for steady-state. A total anode mass of 120 kg per monopile was calculated, with a design life of 25 years. The anodes were distributed on the jacket structure at 3-meter intervals.

Alternatively, impressed current cathodic protection (ICCP) was considered for larger platforms, using mixed metal oxide anodes and a reference electrode feedback system. The ICCP system reduced anode weight by 40% but required power supply and maintenance. For this case, sacrificial anodes were chosen for their simplicity and zero power requirements.

Coating-Cathodic Protection Synergy

The coating system and cathodic protection work together: the coating reduces the current demand for CP by providing a high electrical resistance, while CP prevents corrosion at coating defects. The polarization potential was maintained between -0.80 V and -1.10 V vs Ag/AgCl to avoid hydrogen embrittlement in high-strength steel.

Coating holidays (defects) were minimized through strict quality control during application. The CP system compensated for any remaining small defects, ensuring no localized corrosion. Regular monitoring using ER probes and potential measurement confirmed that the combined system met the NACE SP0169 standard.

Conclusion

This case demonstrates that a well-designed combination of heavy-duty coating and cathodic protection can achieve 25-year maintenance-free corrosion protection for offshore wind steel structures. The synergistic effect reduces overall protection costs and improves reliability.

Additionally, protecting the electronic systems within the turbine from moisture is critical. EJER Tech’s MSD management solutions, with consumable-free and fast-recovery attributes, provide a domestic alternative that enhances the overall durability of offshore wind assets, ensuring seamless operation in harsh marine environments.