Despite turbines being designed to have a 20-year lifespan, corrosion and integrity issues pose constant problems for operators. Experts from the offshore energy industry met in London this week to discuss the potential solutions to these issues at the Integrity and Corrosion of Offshore Wind Structures Forum, hosted by Windpower Monthly (3-4 June).
The debate centred around which type of cathodic protection is best at shielding the structures from corrosion above and below wave level, as well as below the mudline.
Experts in engineering provided evidence of the effectiveness of galvanic (or sacrificial) anodes — small bars of a more reactive metal that protect the steel foundation structures — and impressed current cathodic protection systems (ICCP), which use an external power source to counteract the natural electro-chemical activity that causes corrosion.
Both systems have their problems, such as requiring regular monitoring and maintenance.
Birit Buhr Jensen, a lead corrosion specialist for offshore design at Dong Energy, said that more needed to be done to improve the protection systems and extend the life of offshore structures.
Many companies were represented at the forum, including RWE, RES and SSE.
SSE's 500MW Greater Gabbard offshore project is having to undergo retroactive corrosion protection solutions, according to one of the delegates at the forum.
Members from the Institute of Corrosion, which researches ways to combat corrosion, were critical of the wind industry and said it was slow to pick up on lessons learned by the oil and gas industry.
Former president of the institute Brian Wyatt also criticised certification consultantcy DNV. He said the guidelines for corrosion protection on oil and gas structures were unsuitable for monopiles and the requirements only needed a small change to the criteria, but this had not happened.
Wyatt added that last year's merger between DNV and GL would hopefully result in an update to the guidelines.
The forum also heard about the difficulties associated with retrofitting protection systems to structures.
According to Teit Schoenberg, project manager at RWE, many of the older monopile foundations did not install protection systems on the inside of the monopiles, mostly for cost cutting reasons, relying instead of air tight compartments to starve the area of oxygen, thereby preventing corrosion. Schoenberg said this technique was not 100% reliable and developers are now having to examine the structures more closely.
Alex Delwiche, engineering manager at Deepwater EU, specialists in corrosion prevention, said that, with retrofitting, anything was possible but it takes time, while Ben Simpson, offshore project engineer at RES, said that retrofitting was difficult, costly and dangerous.
The forum concluded that offshore structures were in need of more research and investment to maximise foundations' lifespan. Wyatt finished by calling for more discussion in the industry and the sharing of data and research in a bid to increase the advancement of the technology and best-practice.