Offshore wind energy: BAM and EnBW test corrosion protection on the high seas

With the accelerated expansion of wind energy, the offshore sector is of particular importance. Offshore, however, corrosion in particular endangers the safety and durability of the turbines. The Bundesanstalt für Materialforschung und -prüfung (BAM), together with Energie Baden-Württemberg AG (EnBW), has now launched a unique test campaign to advance the development of protection systems.

Modern offshore wind farms are supposed to remain in operation for 25 years or longer in order to be as economical as possible. But extreme conditions prevail offshore: Corrosion, intensified by the maritime conditions severely affect the turbines, which can be up to 250 metres high. All metallic parts above the waterline are affected by so-called "atmospheric" corrosion. At the same time, the possibilities for protection are particularly limited there.

"The many factors that affect the phenomenon are not yet sufficiently understood, despite long research. Even with known material systems, unexpected problems with corrosion show up again and again and they turn out to be less durable than hoped," explains Martin Babutzka from the Competence Centre Wind@BAM. "This is also due to the fact that forecasts on the durability of materials are mostly based on short-term tests in the laboratory or simulations in climate chambers. Reliable statements on corrosion behaviour under real operation conditions cannot be made on this basis. Often, the results even lead to incorrect assumptions and, as a result, construction elements are designed too conservatively or even too riskily, which in turn affects the economic efficiency and sustainability of the plants."

Martin Babutzka, together with EnBW, the third-largest energy company in Germany, is now starting an experiment that is unique in Germany so far to research atmospheric corrosion in the offshore sector under real conditions. Together with EnBW, the corrosion expert has designed an expsoure campaign in which a total of 17 different materials and corrosion protection systems will be tested for their resistance directly offshore. The results are to be made usable for industry.

For the test campaign, the company Wilhelm Modersohn GmbH & Co. KG built an exposure rack measuring about six by two metres. In this open container-like structure, the material samples were mounted on a scaffolding.

In summer, a supply ship transported the approx. three tonne structure out to the EnBW wind farm "Hohe See", 100 kilometres northwest of Helgoland. There it was hoisted by crane onto a distribution station. On the central platform in the middle of 71 wind turbines, the material samples will be exposed to wind and weather for the next three years.

The test campaign by BAM and EnBW is the most comprehensive of its kind in Germany to date. Material samples made of steel, zinc, copper and aluminium, material variants with innovative coatings and zinc coatings as well as stainless steels in different resistance classes will be tested. All samples were provided by leading companies and associations from the steel construction sector and the galvanising industry. Samples are to be taken and examined for corrosion behaviour at intervals of one year each.

"The campaign allows us for the first time to gain a comprehensive picture of the corrosion conditions offshore as well as truly reliable data on the durability of individual materials. The results should enable companies like EnBW to optimally design corrosion protection in the future. We want to lay a scientific foundation that considers economic as well as ecological aspects," says Martin Babutzka.

"From our perspective, BAM is the ideal partner for this project because, on the one hand, she is involved in the approval of offshore wind turbines and conducts its own research in this area and, on the other hand, it has an excellent reputation and many years of experience in the field of corrosion research and materials technology," says Sven Tannert, an expert from the Quality Assurance Steel Construction and Corrosion Protection department at EnBW.

This article was first published on 8 November by BAM.