Structural health monitoring tools for late and end of life management of offshore wind turbines

The late and end of life stages in an offshore wind turbines (OWT) life cycle have unique features that must be considered. The initial focus on risks associated with start-up issues due to design, manufacturing or process elements gives way to a stable period of operation and maintenance optimisation and service condition monitoring. However, as with other structures, in time the issues of "wear and tear" and remaining life assessment become increasingly prevalent. The dynamics of operating an offshore wind farm varies considerably from existing oil & gas structures. With lower operating margins and the predominance of low redundancy structures, accurate structural health monitoring can play a strong role in safe management and enable increased operating time at end of life and decommissioning. Late life operations of offshore wind farms can pose significant challenges, balancing the potential for rising operations and maintenance costs with the ability to generate significant profitability from increased reliability and longer operations. Improvements in SHM can lead to corresponding improvements in the availability and management of offshore structures. The ability to accurately gather data on damage states and thus remaining life results in significant reduction in repair costs and the determination of cost effective decommissioning plans. Under given scenarios for end of life management and decommissioning there will be various structural systems that will provide hard limits on the viable economic lifetime of OWT and their associated farms. Using a risk based review of age and decommissioning related issues a breakdown of common damage and its causes can be presented, and from this both available and developing SHM techniques to address these late life issues are identified.