Materials Performance

JUN 2016

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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17 NACE INTERNATIONAL: VOL. 55, NO. 6 MATERIALS PERFORMANCE JUNE 2016 Sensor Ring Monitors Welding Seams on Offshore Wind Turbines O ffshore wind turbines—particularly their foundations anchored in the seabed—take a lot of punishment from the environment. Periodically, divers will inspect these structures for defects; however, such checks in the future will be faster and easier to carry out due to a new sensor ring inspection system developed by researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS (Dresden, Germany). The base of a wind turbine, which is located underwater near the seabed, must be able to withstand the severe stresses caused by waves beating against the pylons and winds shaking the rotors. Corrosive saltwater can also damage the foundation. When divers periodically inspect the highly v ulnerable welding seams of the foundation's anchor points, they need to determine if the seams are still in good order, or whether any cracks or defects have appeared that pose a safety risk. To answer these questions, the divers f irst blast the weld with a high- pressure cleaning tool to remove grow th such as algae and crustaceans. Then they apply an electromagnetic f ield to the weld and cover it with iron f ilings. If a crack is present, the electromagnetic f ield will be forced outward and the iron f ilings will accumulate there. This is a diff icult task for the divers, who must carry equipment while swimming against strong currents, and allow themselves enough time to adjust to changing water pressures dur- ing the dive. Currently, the inspection of one wind turbine installation takes about a day. In the future, a box-shaped robotic remote operating vehicle (ROV) will be able to perform this inspection task. The groundwork for this technolog y involves a sensor ring that simplif ies inspection measurements and allows them to be taken automatically, says Andreas Schnabel, project manager with Fraunhofer Institute for Ceramic Tech- nologies and Systems IKTS. The sensor ring is placed around the weld and remains there for the entire service life of the wind turbine, he explains. The ring is composed of numerous sensor elements arranged like a string of pearls with 50- to 70-mm spaces between them. Each of the sensor elements takes its turn function- ing as an actuator. The laborious task of cleaning the area using high pressure is no longer needed. To take the measurements, the diver f irst connects a battery-powered hand- held device to the interface port on the ring, and begins the analysis by pressing a button. (In the future, this task will be performed by the robot.) The f irst sensor sends ultrasonic waves into the weld, which then permeate the entire structure. The waves pass unobstructed through the intact areas; however, if there is a crack Information on corrosion control and prevention The movable sensor ring can locate cracks in offshore wind turbine foundations. Photo © Fraunhofer IKTS. Researchers ftted a test pipe knot in the Baltic Sea with two sensor ring demonstrators for practical trials. Photo © Fraunhofer IKTS. Continued on page 18

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