Vykintas Samaitis received M.Eng. degree in measurements engineering and a Ph.D. degree from Kaunas University of Technology, Lithuania, in 2012 and 2016 respectively. He has hands-on experience on a wide variety of international projects including but not limited to ultrasonic inspection of adhesive joints, spot welds, piping networks and composites. Since 2016 he is a researcher at non-destructive testing research group at Ultrasound Research Institute. His current interests include long-range guided wave inspection, structural health monitoring, material characterization, numerical modelling, signal processing and phased array imaging.
CASS Microstructure reconstruction
NDE techniques based on ultrasonic waves are widely used throughout NPP industry to detect defects such as cracks and to prolong the usage of defected components that doesn’t require replacement yet. Each inspection technique needs a qualified procedure, which ensures that it’s capable of detecting defects of specific type and size. However, complex and heterogeneous structures of coarse grained castings significantly degrade the performance of ultrasonic techniques. This is due to microstructures with large grains, inducing scattering of the ultrasonic waves at grain boundaries, which is responsible for both structural noise and attenuation. Local variations of grain size and orientation lead to different ultrasonic responses and limited applicability of the inspection procedures. Hence, the inspection qualification needs to cover range of grain sizes and their distributions for each specific component. This forms a need for a metric to estimate grain size and its distribution from the measurements that could be taken on-site.
In this presentation we discuss several approaches how the mean grain size can be evaluated from attenuation measurements. By combining the results from metallographic evaluation, modelling and experimental measurements we demonstrate the importance of volumetric grain size distribution and non uniqueness of attenuation metric at different combinations of grain statistics. Finally, we discuss alternative metrics and measurement approaches that could be used for assessment of grain properties and their suitability on-site.
TRL (transmit-receive-longitudinal) transducers are the method of choice for the inspection of coarse grain cast austenitic stainless steel. Employing both an angle in the incidence plane and a roof angle, TRL transducers reduce the effective material volume generating backscatter that actually makes it back to the receiver. Introduced in early 1990s TRL transducers currently available as linear or asymmetrical matrix arrays that allow to cover different depth ranges with a single transducer. Novel TRL array technologies allow to apply advanced imaging algorithms to even further improve the S/N ratio of reconstruction. However, the potential advantages of combining TRL with advanced imaging methods, especially those derived from TFM, are not well documented yet. In this presentation we investigate the potential of TFM and super resolution methods applied on TRL inspection of heterogeneous nuclear materials. The improvements in S/N ratio, reconstruction depth and overall decrease of structural noise is demonstrated with the experimental results on NPP relevant mock-ups. With the advent of phased array technology, we discuss 0° incidence TRL arrays, that allow to streer the beam in frontal direction and to focus at different depths dynamically, without using application specific set of wedges.