A new report from Lloyd’s Register (LR) reveals that critical support structures in some offshore wind turbines (OWTs) may not meet their expected fatigue life, potentially impacting the long-term operational integrity and safety of these assets. The study, which evaluated a 500-600 MW North Atlantic offshore wind farm comprising 60-70 turbines, found that a key joint in a jacket foundation could reach the end of its fatigue life after just 52 years, significantly short of the industry’s typical 75-year design requirement based on a fatigue design factor of three for a 25-year service life.

Instead of advocating for immediate structural redesign, the LR study champions a Reliability-Based Inspection (RBI) approach. This method aims to identify and mitigate potential failures through targeted, risk-based maintenance, thereby optimizing asset life and ensuring safety. The RBI framework integrates an S-N (Stress vs. Number of cycles) model to predict when structural safety thresholds may be breached, alongside Fracture Mechanics (FM) crack growth analysis to forecast the probability of failure over time. This sophisticated approach allows inspection schedules to be dynamically updated by incorporating real-world inspection results via Probability of Detection (PoD) curves, making maintenance more responsive to actual conditions.

The case study suggests that an initial inspection could be necessary around the ninth year of operation. Subsequent inspections might then be required annually, depending on the chosen inspection methodology, to maintain acceptable safety margins. However, the report also underscores the limitations of conventional visual and ultrasonic inspection techniques for fatigue-critical components. It highlights that more advanced methods, such as Eddy Current or ACFM (Alternating Current Field Measurement), offer superior reliability and enable longer inspection intervals, albeit sometimes requiring operators to accept slightly lower safety thresholds.

Implementing RBI planning effectively requires substantial expert input, robust models, and advanced software tools capable of handling complex calculations. Ongoing research is crucial to refine these models and address practical challenges, particularly in reliability updating and the precise calibration of parameters like initial crack size and stress intensity factors, which are often underdeveloped in current industry practices.

Kourosh Parsa, Global Head of Technology of Offshore and Subsea at LR, emphasized the findings: “Many offshore wind assets are designed to a standard fatigue factor, but real-world conditions often expose critical vulnerabilities. Our findings show that using reliability-based methods allows operators to focus inspections where the risks are greatest. By integrating sophisticated models and real-world inspection data, we can extend asset life, reduce costs, and, most importantly, maintain safety.” Manuel Ruiz, Head of Offshore Renewable Solutions at LR, added, “By focusing on the areas with the greatest risk, we can not only help to manage fatigue-related issues more effectively—we’re also enabling developers and operators to make better-informed decisions that optimize asset life and performance.” The study calls for broader industry collaboration to refine inspection standards, share real-time monitoring data to enhance fatigue predictions, and adopt more flexible definitions of acceptable reliability where appropriate, ensuring the long-term viability of offshore wind investments.