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Offshore foundation monitoring by guided waves - challenges and perspectives

: Weihnacht, Bianca; Frankenstein, Bernd; Gaul, Tobias; Neubeck, Robert; Schubert, Lars

Fulltext urn:nbn:de:0011-n-5038879 (568 KByte PDF)
MD5 Fingerprint: 17374d4db7e87b7e97ac4840ccb92912
(CC) by-nd
Created on: 4.8.2018

Purschke, M. ; International Committee for Non-Destructive Testing -ICNDT-; Deutsche Gesellschaft für Zerstörungsfreie Prüfung e.V. -DGZfP-, Berlin:
19th World Conference on Non-Destructive Testing, WCNDT 2016 : Munich, Gemany, 13-17 June 2016; Proceedings; USB-Stick
Berlin: DGZfP, 2016 (DGZfP-Berichtsbände 158)
ISBN: 978-3-940283-78-8
Paper 15, 8 pp.
World Conference on Non-Destructive Testing (WCNDT) <19, 2016, Munich>
Conference Paper, Electronic Publication
Fraunhofer IKTS ()
structural health monitoring

Offshore-foundations for wind turbines are expected to increase in significance over the coming years. Various wind parks are already producing energy. There are many more planned or currently being built. The maintenance of these offshore wind turbines is challenging due to limited accessibility and expensive logistics. Currently, 25% of these structures have to be evaluated each year regarding their condition and stability. For this task, welded seams are in the focus of interest. At the moment, they are visually inspected by divers, in the oil and gas industry Alternating Current Focusing Technique (ACFM) is used as well. None of these are applicable e.g. on the inside of jackets due to safety issues. Visible inspection is often limited by the sight conditions and ACFM can only measure directly under the sensor. The Fraunhofer IKTS therefore developed a transducer ring to be placed permanently on the foundations of offshore wind turbines. It is well suited especially for the monitoring of jackets. The measurement device CoMoSeam has been tested underwater successfully. Furthermore, an artificially initialized crack could be detected and located correctly. The investigation is realized by guided waves which have a lower frequency range than commonly used NDT techniques. The advantage lies in the longer range and the therefore reduced number of sensors. Nevertheless, the resolution is decreased but still far better than achieved by the currently used inspection methods. This paper presents the hardware used for building the sensor ring as well as the measurement technique. Especially the lamination to ensure water proof equipment is challenging regarding the demanded large diameters for offshore platforms. To detect cracks correctly even in harsh environments, a sophisticated data processing is necessary to eliminate all obviously incorrect data automatically. The method is just being introduced in the regulations and will be adapted to a diver free installation and operating regime.