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Nondestructive testing of gas turbine blades is essential for their maintenance and service process which is critical to ensure both safety and efficiency of these highly stressed parts. In this presentation, a novel ultrasonic testing method is explored in order to acquire part thickness information in the turbine blade’s airfoil. In established industry processes, the measurements are mainly carried out manually and only at a few specific positions of the inspected parts. The proposed method scans the part using a robot arm guiding an ultrasonic array sensor. For ultrasonic coupling to the complex-shaped surface geometry, the inspected part and sensor are immersed into water. A two-step TFM[1, 2] (Total Focusing Method) approach is used to reconstruct the outer and inner surfaces subsequently from the ultrasonic raw data, which are acquired using the FMC[3] (Full Matrix Capture) measurement principle. For each sensor position, the location and geometry of the outer surface is first identified and then used to create an image of an area inside the material. From that image, the inner surface is reconstructed. Finally, part thickness information is deducted from merging location data of inner and outer surface. The result is a high resolution, high precision mapping of the inspected part’s wall thickness.
Usability of the written procedures: an eye tracking study Non-destructive evaluation (NDE) is regarded as one of the key elements in ensuring quality of engineering systems and their safe use. A failure of NDE to detect critical defects in safety-relevant components, such as those in the nuclear industry, may lead to catastrophic consequences for the environment and the people. NDE inspection procedure is one of the most important tools in the everyday life of an NDE inspector. Experience and research studies have shown that NDE procedures are not always used as foreseen and may need to be optimized. Both the content and format play an important role in producing reliable procedures. Whereas the content aids in the understanding of the task and in its subsequent correct execution, the format determines the efficiency and frequency of the procedure’s use.
For the purposes of this study, an inspection procedure - designed to be used in the inspection of components used in the final disposal of spent nuclear fuel - was further developed by adopting a user-centered design. This was achieved by following the eye movements during a data evaluation task whilst using the procedure, by interviews and group discussions, accompanied by a review from a human factors’ perspective, the suggestions from relevant literature and by reiterating the entire process once again. This process resulted in identifying shortcomings and in suggesting alterations to the existing procedure. The newly created procedure was empirically tested for its usability using eye tracking. By comparing the old instruction format to the newly developed one, the results showed that appropriately highlighting warnings, exceptions, or reminders, and placing them at a logical position assures that they will be read and identified with ease rather than overlooked. The presentation of the information in a stepwise manner, with one action per step, allows the user to follow more easily the steps that must be carried out to save time and effort.
This study - the first of its kind in the field of non-destructive evaluation - showed that the procedure can be improved by applying human factors principles to the design and by involving the users into the process of procedure development and quality assurance.
Introduction of the speaker – Marija Bertovic
Marija Bertovic has a degree in psychology and a PhD in human factors. Since 2006 she has been working on topics related to human factors in non-destructive testing at the BAM Federal Institute for Materials Research and Testing, German Society for Non-Destructive Testing and as an independent consultant. The focus of her research has been on identifying and studying human factors’ related risks during NDT inspections and suggesting ways of optimizing the inspections and inspection procedures. She is currently a research staff member at BAM responsible for probabilistic safety and reliability analyses AND human factors analyses. She is the chairwoman of the German Society for Non-Destructive Testing’s (DGZfP) subcommittee on human machine interaction and the winner of the DGZfP Science Award in 2018.
Construction methods, environmental stressors, and aging factors are the main causes for defects of reinforced concrete in nuclear power plants (NPP). These defects are typically occurred as corrosion of reinforcement steel, delamination, cracks, malfunction of post-tensioning or steel composite systems etc. Some of the challenges for assessing the performance of these structures by nondestructive testing methods (NDT) are that the assessment could be performed only during the annual overhauls when testing is time-limited and uncertainty of the accuracy and reliability of the available NDT testing devices combined with the lack of the international uniformity of the methods used for NDT tests. To overcome these challenges, a mock-up wall representing a section of the concrete containment of the NPP was built. The mock-up wall included simulated defects, which mimic the most common types of defects in NPP concrete structures such as dimensional errors, honeycombing, delamination, defects adjacent to the steel liner and voids in grouted tendon ducts for the post-tensioned structures. This paper introduces the design and construction of the wall including the concrete properties, reinforcement, tendon ducts and the types of the simulated defects. The paper also introduces the NDT methods and techniques that are suitable for assessing the condition of the mock-up wall under the real environmental conditions. These techniques include mechanical methods as rebound hammer, ultrasonic and electromagnetic methods. This mock-up wall will enable to investigate reliably available NDT methods and experts’ skills providing also an important and very much need educational platform for future NDE experts.
The objective of the report is to present the state-of-the art of non-destructive testing methods and technologies for the inspection of thick, heavily-reinforced structures, (e.g. found in nuclear power plants). Wall thicknesses can be in excess of one meter and the structures often have increased steel reinforcement density. The accessibility for any testing method may be limited due to the presence of liners and other components such as cast-in-place items. Testing methods have to provide solutions for tasks such as locating failure (inclusions, corrosion, voids, delaminations) in the structures or the assessment of the condition of the structure in general.
GMR sensors are increasingly used for magnetic surface inspection due to their high sensitivity and high spatial resolution. In case of simple planar or cylindrical shaped components, the GMR-based inspection procedure can be automated easily. We present GMR measurements of real fatigue cracks. In addition, we present a probe design using a local magnetization unit and commercially available GMR sensors. The design was carried out by means of finite-element method (FEM) simulations. Using the local probe we measured bearings containing artificial reference cracks of different depths and orientations. Cracks with a depth of 40 µm could be resolved with a signal-to-noise ratio better than 6. A further reduction of the measuring time can be obtained using a sensor array. For this purpose we present a study of the optimized size of the sensing GMR-layers for a NDE-adapted sensor array. The geometric sensor parameters were investigated through simulations of the magnetic flux leakage of surface cracks using an analytic model.
X-ray computed tomography is an important tool for non-destructively evaluating the 3-D microstructure of modern materials. To resolve material structures in the micrometer range and below, high brilliance synchrotron radiation has to be used. The Federal Institute for Materials Research and Testing (BAM) has built up an imaging setup for micro-tomography and -radiography (BAMline) at the Berliner storage ring for synchrotron radiation (BESSY). In computed tomography, the contrast at interfaces within heterogeneous materials can be strongly amplified by effects related to X-ray refraction. Such effects are especially useful for materials of low absorption or mixed phases showing similar X-ray absorption properties that produce low contrast. The technique is based on ultra-small-angle scattering by microstructural elements causing phase-related effects, such as refraction and total reflection. The extraordinary contrast of inner surfaces is far beyond absorption effects. Crack orientation and fibre/matrix debonding in plastics, polymers, ceramics and metal-matrix-composites after cyclic loading and hydro-thermal aging can be visualized. In most cases, the investigated inner surface and interface structures correlate to mechanical properties. The technique is an alternative to other attempts on raising the spatial resolution of CT machines.