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Photo: REpower

INDUSTRIAL SERVICES | WIND ENERGY

Strategies for the Fight Against Corrosion

Strong currents, salt water, ice, high wind speeds: Offshore wind turbines are exposed to extreme conditions. To avoid excessive maintenance costs and downtime, operators must implement long- term anticorrosion programmes

C onstant high winds on the open sea are what makes offshore wind generation appealing. But to operate profitably, wind turbines must be designed to resist the onslaught of the elements for many years and run relia- bly without requiring costly maintenance and repairs. Cor- rosion protection is a key factor in ensuring the longevity of these systems – a topic discussed in depth during the 8th conference on corrosion protection in maritime engineer- ing this January.

Continuous Monitoring

“As wind turbines get bigger and bigger, boasting name- plate ratings of five megawatts and beyond, it is neces- sary to tune all relevant parameters accordingly,” said Uwe Meesenburg of REpower Systems. The quality and production control expert specializing on tubular tower design and corrosion protection was referring to two pilot projects, “Beatrice” in the North Sea, and “Thornton Bank” in the English Channel. REpower supplied the tubular to- wers, nacelles and rotors for both units.

While REpower did not have to address the issues as- sociated with the high-stress sections of the foundations below the waterline and in the range between the low and high water levels, these projects involved other technical challenges no less demanding: How can the components be protected against corrosion? How can they be trans- ported and assembled? Are there any manufacturers ca- pable of building tubular towers of these dimensions and protecting them with effective anticorrosion coatings?

In the case of the Beatrice project, the tower segment is 66 metres long. This “tube” had to be cut into three sections to fit into the sandblasting and paint shops. But thanks to its excellent planning work and precise execution, REpower succeeded in providing a reliable coating. The repair sys- tem supplied by the paint manufacturer allowed the an- ticipated nicks and marks caused during the transport and assembly to be eliminated.

In the case of Thornton Bank, however, the tower manu- facturer initially failed to meet the stringent requirements of REpower. In particular, the use of shop-primed plates was not consistent with specifications. Yet, by cooperating closely, REpower, the tower manufacturer and the supplier of the steel plates were ultimately able to deliver a high- quality product. “What all this shows is that uncompromis- ing quality and production control is crucial, especially so in the area of corrosion protection,” said Meesenburg. “It will take time as well as larger batch sizes to achieve a truly reliable process.”

To provide an effective repair system for cases of dam- age, it is essential to document all corrosion protection measures. This includes instructions for surface prepara- tion when restoring the necessary coating layers. “There are very few tower manufacturers that are technically ready to meet the challenges,” Meesenburg emphasized. After all, building production facilities for these enormous tubular tower segments takes substantial capital investment.

Low Maintenance

SUCCESS. At the project “Beatrice”, good planning and exact realization lead on to a reliable coating.

“Any wind turbine should be designed to operate for 20 to 25 years without requiring much maintenance,” said Mathil- de Lindhardt Damsgaard of Danish energy company Dong. “So when a corrosion protection system is selected, every single parameter must be scrutinized.” Ensuring a level of protection that is both economical and durable means examining each specific project and component individu- ally. No matter whether the structure is made of concrete or steel, selecting the right materials and design features is the first step to minimizing the risk of corrosion, Damsgaard adds.

The strengths and weaknesses of an anticor- rosion system will not become apparent until the offshore wind turbine has been in operation for

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nonstop 02/2009

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