On-site inspection of wind turbine blades using shearography with a robotic deployment system
J Gao, H Zheng, V Rosas, M Pachos, J Seton and X Echarte Azcarate
Wind energy is a fast growing industrial sector. As wind turbines are expected to work 90% of the time during a typical lifetime of 20 years, structural flaws are of great concern, particularly for blades. Repairing or replacing a blade is always difficult, especially for large wind turbines. The downtime of a wind turbine installation due to a blade failure usually lasts 4-6 days or longer if due to electrical or mechanical failure within the nacelle. Cracks in the blades sometimes appear soon after manufacture. Defects also can be produced during transportation. Current inspection of wind turbine blades is mainly reliant on sending an engineer via rope access.
An ideal solution to this problem is to utilise a compact robot that can reach the blade and implement faster inspections on site. Shearography has long been recognised as a powerful inspection technique and has found wide application in a range of industries, including the aerospace, automotive and shipbuilding sectors. However, conventional shearography still needs a relatively stable environment, thus it is difficult to use for on-site wind turbine blade (WTB) inspections.
In this paper the authors that is able to climb along the wind tower is developed. A vacuum suction-based end-effector is also developed, which sits on top of the platform and enables the shearography system to be deployed on the WTB surface during inspection. Two successful field trials were performed in this year at the CRES wind farm in Greece. The first trial was carried out on 20 April 2019, after which a second trial was performed. During the test, the weather was changing from low wind speed (3-5 m/s) to above 10 m/s, which is the up limit for wind turbine maintenance and inspection. Nevertheless, the position was reached and a few speckle pattern video clips were recorded in half an hour. Afterwards, the test had to be stopped and the robotic platform retracted. After post-processing of the recorded video clips, shearographic fringe patterns could be seen. To the authors’ knowledge, this was the first time in the world that shearography fringe pattern was obtained from an on-site inspection on a wind turbine tower. It demonstrated that their overall approach of using shearography with a robotic system for WTB inspection is working. The second field trials occurred on 13-14 May 2019, where more speckle pattern videos of the WTB after thermal stressing by a heat gun were collected, and more shearography fringe patterns were obtained. This further demonstrated that shearography can be used for on-site WTB inspection.
An ideal solution to this problem is to utilise a compact robot that can reach the blade and implement faster inspections on site. Shearography has long been recognised as a powerful inspection technique and has found wide application in a range of industries, including the aerospace, automotive and shipbuilding sectors. However, conventional shearography still needs a relatively stable environment, thus it is difficult to use for on-site wind turbine blade (WTB) inspections.
In this paper the authors that is able to climb along the wind tower is developed. A vacuum suction-based end-effector is also developed, which sits on top of the platform and enables the shearography system to be deployed on the WTB surface during inspection. Two successful field trials were performed in this year at the CRES wind farm in Greece. The first trial was carried out on 20 April 2019, after which a second trial was performed. During the test, the weather was changing from low wind speed (3-5 m/s) to above 10 m/s, which is the up limit for wind turbine maintenance and inspection. Nevertheless, the position was reached and a few speckle pattern video clips were recorded in half an hour. Afterwards, the test had to be stopped and the robotic platform retracted. After post-processing of the recorded video clips, shearographic fringe patterns could be seen. To the authors’ knowledge, this was the first time in the world that shearography fringe pattern was obtained from an on-site inspection on a wind turbine tower. It demonstrated that their overall approach of using shearography with a robotic system for WTB inspection is working. The second field trials occurred on 13-14 May 2019, where more speckle pattern videos of the WTB after thermal stressing by a heat gun were collected, and more shearography fringe patterns were obtained. This further demonstrated that shearography can be used for on-site WTB inspection.
