The implementation of efficient maintenance strategies of thin-walled structural components require reliable damage detection and localization techniques. In particular, guided ultrasonic waves technology represent an auspicious approach when implemented in a structural health monitoring system. The method is usually based on distributed sensing with piezoelectric elements that act in turn as ultrasound transmitter and receiver. This work aims at a unifying framework for damage localization considering algorithms from different scientific disciplines, e.g. originated from radar and geophysics. Here, we systematically express those algorithms in matrix form and compare the respective damage localization performance with experimental measurements considering an isotropic specimen with a single and also multiple simultaneous defects. In addition, we evaluate the algorithms’ point spread function and propose performance metrics to quantitatively compare the imaging success.

In order to reduce the CO2-emissions and to increase the energy efficiency, the operating temperatures of power plants will be increased up to 720°C. This demands for novel high-performance steels in the piping systems. Higher temperatures lead to a higher risk of damage and have a direct impact on the structure stability and the deposition structure. Adequately trusted results for the prediction of the residual service life of those high strength steels are not available so far. To overcome these problems the implementation of an online monitoring system in addition to periodic testing is needed. RWE operates the lignite power plant Neurath. All test and research activities have to be checked regarding their safety and have to be coordinated with the business operation of the plant. An extra bypass was established for this research and made the investigations independent from the power plant operating. In order to protect the actuators and sensors from the heat radiate d from the pipe, waveguides were welded to the bypass. The data was evaluated regarding their dependencies on the environmental influences like temperature and correction algorithms were developed. Furthermore, damages were introduced into the pipe with diameters of 8 mm to 10 mm and successfully detected by the acoustic method

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Offshore foundations for wind turbines are expected to increase in significance over the coming years. Various wind parks are already producing energy and there are many more planned or currently being built. The maintenance of these offshore wind turbines is challenging due to the 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 the focus of interest. At the moment, they are visually inspected by divers; in the oil and gas industry, the alternating current field measurement (ACFM) technique is used as well. None of these are applicable on the inside of jackets, for example, 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 has therefore developed a transducer ring to be placed permanently on the foundations of offshore wind turbines. It is particularly well suited for the monitoring of jackets. The measurement device, CoMoSeam, has been successfully tested underwater. Furthermore, an artificially-initialised crack could be detected and located correctly. The investigation is realised by guided waves, which have a lower frequency range than the commonly used ultrasound techniques. The advantage lies in the reduced number of sensors compared to NDT ultrasound techniques, which also leads to a lower resolution. Nevertheless, the resolution is decreased but is still far better than that achieved by the currently used inspection methods. This paper presents the hardware used for building the sensor ring as well as the measurement technique. The lamination required to ensure that the equipment is waterproof is especially challenging due to the large diameters demanded for offshore platforms. To detect cracks correctly, even in harsh environments, sophisticated data processing is necessary to automatically eliminate all obviously incorrect data. The method is just being introduced in the regulations and will be adapted to a diver-free installation and operating regime

The operation efficiency and safety of pressure vessels in the oil and gas industry profits from an accurate knowledge about the inner filling distribution. However, an accurate and reliable estimation of the multi-phase height levels in such objects is a challenging task, especially when considering the high demands in practicability, robustness in harsh environments and safety regulations. Most common systems rely on impractical instrumentation, lack the ability to measure solid phases or require additional safety precautions due to their working principle. In this work, another possibility to determine height levels by attenuation tomography with guided elastic waves is proposed. The method uses a complete instrumentation on the outer vessel shell and is based on the energy conversion rates along the travel path of the guided waves. Noisy data and multiple measurements from sparsely distributed sensor networks are translated into filling levels with accuracies in the centimeter range by solving a constrained optimization problem. It was possible to simultaneously determine sand, water, and oil phases on a mock-up scale experiment, even for artificially created sand slopes. The accuracy was validated by artificial benchmarking for a horizontal vessel, giving references for constructing an affordable prototype system.