THE IMPORTANCE OF CORROSION, CATHODIC PROTECTION, AND FATIGUE MONITORING FOR LATE-LIFE WIND FARMS 

MATERIALS AND COATING EVOLUTION

The structures are typically constructed of steel, or a combination of concrete gravity bases with steel supporting the turbines and infrastructure. Most steel surfaces now utilise protective coatings, although initially there were submerged sections that were left uncoated and bare; these relied wholly on cathodic protection. More recently, many of the submerged sections are being coated externally and even internally. A CP system is still required, albeit minimised compared with those without a coating system. 

Early designs relied primarily on corrosion allowances rather than coatings and cathodic protection. However, several assumptions specific to these new structures and many early wind turbine fields were unproven. In the late 2000s and early 2010s, concerns were raised as the fields became more expansive, with larger structures located in more aggressive environments such as in the North Sea between Denmark, Germany, and the UK. Through inspection and short-term corrosion, it was established that serious corrosion concerns were lurking in the internal flooded structures; for some operators, further studies were undertaken and remediation programmes such as the installation of internal CP systems were implemented.  

Structural integrity and challenges 

Some of the earlier monopile-type flooded structures’ issues were further exacerbated by structural instability caused by harsh environments and a lack of understanding of the effects of turbine vibrations on the foundations, resulting in serious concerns about both structural viability and corrosion integrity.   

Consequently, many of today’s wind farm structures are now being fitted with an array of structural, corrosion and CP monitoring systems. One vigilant operator is now introducing the integration of a single remote system for monitoring multiple sample wind structures into their new-build projects.  

One of the first introductions of a CP system inside monopile structures proved complicated because it was acidifying the water using the more efficient aluminium anodes commonly used for external protection on offshore structures. However, this important information was detected by short-term, intensive remote monitoring, which allowed the concern to be relayed to the corrosion community. Without this level of monitoring, the problem may not have been detected for many years and other underlying problems could have otherwise occurred without this knowledge. Subsequently, after this well-documented study, the industry has been able to adapt accordingly by avoidance of flooding, coating whilst reducing the CP requirement, continuing remote monitoring, and performing annual inspections. However, the latter requires ongoing personnel support.