Plane Wave Imaging Techniques for Immersion Testing of Components With Nonplanar Surfaces

Abstract

Plane Wave Imaging (PWI) is an ultrasonic array imaging technique used in non-destructive testing, that has been shown to yield high resolution with few transmissions. Only a few published examples are available of PWI of components with nonplanar surfaces in immersion. In these cases, inspections were performed by adapting the transmission delays in order to produce a plane wave inside the component. This adaptation requires prior knowledge of the component geometry and position relative to the array. The current paper proposes a new implementation, termed PWI Adapted in Post-Processing (PWAPP), which has no such requirement. In PWAPP the array emits a plane wave as in conventional PWI. The captured data is input into two post-processing stages. The first reconstructs the surface of the component, the latter images inside of it by adapting the delays to the distortion of the plane waves upon refraction at the reconstructed surface. Simulation and experimental data are produced from an immersed sample with a concave front surface and artificial defects. These are processed with conventional and surface corrected PWI. Both algorithms involving surface adaptation produced nearly equivalent results from the simulated data, and both outperform the non-adapted one. Experimentally, all defects are imaged with Signal-to-Noise Ratio (SNR) of at least 31.8 and 33.5 dB for respectively PWAPP and PWI adapted in transmission, but only 20.5 dB for conventional PWI. In the cases considered, reducing the number of transmissions below the number of array elements shows PWAPP maintains its high SNR performance down to number of firings equivalent to a quarter of the array elements. Finally, experimental data from a more complex surface specimen is processed with PWAPP resulting in detection of all scatterers and producing SNR comparable to that of the Total Focusing Method. Index Terms-ultrasound, non-destructive evaluation, plane wave imaging, immersion testing, signal processing, complex geometry.Rosen K. Rachev was born in Burgas, Bulgaria, in 1993. He received the M.Eng. degree in Mechanical Engineering from the University of Bristol, Bristol, U.K., in 2016. He is currently pursuing the D.Eng. degree in Nondestructive Evaluation in the Ultrasonics and Nondestructive Testing Research Group, University of Bristol. He is working on advanced ultrasonic data processing algorithms for pipeline in-line inspections, and his project is sponsored by Baker Hughes. His research interests include nondestructive evaluation for the oil and gas industry, ultrasonic phased array surface reconstruction, adaptive imaging, and defect characterisation.

Deep Learning for Ultrasonic Crack Characterization in NDE

“…A ray-based model is used to simulate the Full Matrix Capture (FMC) data, tracing all relevant paths (direct and half skip) from the array to the defect and using scattering matrices to calculate the phase and amplitude of its reflections [26], [30]. The FMC dataset, , , is used to generate PWC data, ℎ , , with…”

“…To simulate defect responses accurately a local FE model is used to generate scattering matrices [25]. Then, to efficiently create Plane Wave Capture (PWC) data a ray-based model [26] is used. The structural and grain noise is included by gathering experimental PWC data from a defect-free steel plate and adding it to the simulated data [27] which is then filtered and imaged.…”

Plane Wave Imaging through Interfaces

“…This acquisition mode is called Full Matrix Capture (FMC). Another method that requires less transmissions is the Plane Wave Imaging (PWI) [ 5 , 6 , 7 , 8 ], achieving higher image rates. In this method, each transmission uses all array elements to produce a plane wave in a specified direction.…”

“…This is the case of immersion testing, and also when a wedge is used between the array and the part under test. Computing the focal laws accounting for this refraction complicates the plane wave image formation process, and several authors have addressed the associated performance and frame-rate limitations [ 6 , 7 , 8 , 9 , 10 , 11 ]. For the Phased Array (PA) method, the focal laws can be computed using the concept of a virtual array ([ 9 , 10 , 11 ]), which is an approximation that significantly reduces the computational cost.…”

“…In [ 6 , 7 , 8 ], the authors show how plane waves can be generated inside a test piece with a complex interface, with previously known shape. In [ 8 ], they also propose the method PWAPP (Plane Wave Adapted in Post Processing), which does not require previous knowledge of the interface. Instead, an FMC capture is used, and the interface is reconstructed from this data.…”