The production and use of hydrogen in the chemical and transportation industries has increased in recent years in efforts to curb greenhouse gas emissions and to make productive use of industrial waste.&nbsp; For many applications, the preferred storage method for hydrogen is as a pressurized gas in metal-lined pressure vessels.&nbsp; Storage of hydrogen is challenging due to interactions between hydrogen ions and the metallic vessel liner, which can result in embrittlement and hydrogen enhanced localized plasticity.&nbsp; These interactions impact how damage develops in the microstructure prior to cracking and how quickly cracks propagate after initiation.&nbsp; Only the latter has been related to the output from non-destructive testing to affect time in service.&nbsp; &nbsp;In this study, we examine how differences in the pre-cracking fatigue behavior observed in steel loaded in hydrogen rich environments affect measurements of acoustic nonlinearity.&nbsp; &nbsp;&nbsp;For this study, a set of SA-372 Grade J steel compact tensile specimens were cut from a commercial ASME Type II pressure vessel.&nbsp; The specimens were cyclically loaded to induce fatigue damage under two conditions: (1) exposed to ambient air and (2) exposed to pressurized hydrogen gas at 3000 psi.&nbsp; One set of specimens was cycled to 20, 40, 60, and 80% of the number of cycles to crack initiation in each exposure condition.&nbsp; Early stage damage was evaluated using the second harmonic ratio, examined using through-thickness measurements made with commercial piezoelectric transducers and a high-power ultrasonic instrument.&nbsp; &nbsp;The results show differences in the growth of the acoustic nonlinearity parameter in materials exposed to hydrogen, and in the values reached prior to crack initiation.&nbsp; By providing an understanding of how nonlinearity develops in hydrogen-exposed steel, this study provides the first step toward early-fatigue monitoring and life extension in hydrogen infrastructure.

Second Harmonic Generation in Pressure Vessel Steel Fatigued in Hydrogen

The macroscopic mechanical properties like yield-strength, ductility or hardness play an important role during the steel production and the design of new steel grades. The austenite grain size is an important parameter, which influences the final microstructure and the properties of the material. When developing grain growth evolution models, typically many samples have to be treated thermally and micrographs have to be prepared ex situ. To reduce the time expenditure of this procedure we carried out in-situ laser ultrasound measurements of austenitic grain growth.&nbsp; A thermomechanical simulator of the type LINSEIS L78 has been upgraded with a laser ultrasound measurement system, which enables the continuous and contactless determination of the austenite mean grain size during a thermal cycle.Acoustic waves propagating in a polycrystalline material, are attenuated by various physical phenomena. At ultrasonic frequencies, the major attenuation contribution stems from the scattering of the elastic waves at the boundaries between adjacent grains. This scattering induced attenuation depends on the ratio between the wavelength and mean grain size D. If the attenuation coefficient can be determined, conclusions can be drawn about D using heuristic models based on well-established mean-field attenuation theories. In classical attenuation models, three asymptotic cases are defined. For these cases, the frequency dependent longitudinal attenuation can be described by a power-law of the form α(f) = a + CD^n-1f^n-1, where n can take the values of 4 (Rayleigh regime), 2 (Stochastic regime) or 0 (Geometric regime). &nbsp;However, in ultrasonic attenuation measurements, the acoustic frequencies/wavelength often falls within a transition region and the asymptotic power-law formulas are not applicable. In particular, this may happen when grain growth is studied. Moreover, it was recently shown, that in addition to the mean grain size, also the grain size distribution has an influence on the attenuation. This may change the exponent n even for asymptotic cases.In this work, we will show the calibration workflow and grain size results by a new attenuation model based on the power-law formula for the plain carbon steel (DIN 1.1191/AISI 1045). Therefore In-situ laser ultrasound measurement data is compared with several micrographs defined at supporting points along a specified temperature program in the thermomechanical simulator. Additional in-situ laser ultrasound measurements were carried out on different temperature profiles in order to show the robustness of the application. The measured mean grain size from the laser ultrasound experiments were compared with the measured mean grain size from the analyzed micrographs.

In-Situ Laser Ultrasound Measurements of Austenitic Grain Growth in Plain Carbon Steel

Elastic waves which are propagating in polycrystals are permanently scattered at the boundaries between adjacent grains, due to an abrupt change of acoustic material properties caused by changing crystallite orientation. This leads to a macroscopic, measurable spatial attenuation in propagation direction, which is related to details of the microstructure (e.g. the average grain size) and thus might be used for its characterization. On the other hand, wave scattering leads to amplitude fluctuations (grain-noise) of ultrasonic signals, and thus hinders flaw detection. A deep physical understanding is thus vital for the development and improvement of non-destructive evaluation (NDE) techniques. Here, we present a numerical method to investigate the grain boundary scattering induced effective attenuation of Rayleigh-type surface acoustic waves (SAWs) in a virtual digital twin of a real metal sample.Although the idea of using ultrasonic attenuation measurements for microstructure characterization exists for more than half a century, even today no direct extraction of the statistical moments of the microstructure by inversion of acoustic attenuation measurements has been achieved. One reason for this is that a reliable and reproducible measurement of the effective acoustic attenuation, in accordance with analytical mean-field attenuation theories, is difficult. In most experimental studies, longitudinal bulk waves are used. In a recent study, we presented a non-contact method for the determination of Rayleigh-type surface acoustic wave attenuation in polycrystalline metals. It is based on a frequency domain Laser-Ultrasound (LUS) system. The obtained frequency dependent SAW attenuation showed good quantitative agreement to analytical models, but a slightly different frequency power-law in the stochastic scattering regime.Here, we present a novel approach to study the effective SAW attenuation with finite element method (FEM) model based on a realistic material model. It depends on statistically matching a virtual polycrystal based on a Laguerre-tessellation with a previously experimentally studied aluminum sample. Therefore, the spatial autocorrelation functions of the real and virtual microstructures are matched. Signal-processing methods are presented to extract the effective SAW attenuation from the FEM-data. Finally, comparisons to the previous experimental results are made and conclusions are drawn.

Finite Element Modelling of Effective Surface Acoustic Wave Propagation in a Digital Twin of a Polycrystalline Aluminum Sample

Ultrasonic phased array imaging is an invaluable tool in Non-Destructive Testing, allowing for the assessment of quality and internal integrity of components. The golden standard in ultrasonic imaging is currently considered to be the Total Focusing Method (TFM), where a Full Matrix Capture (FMC) dataset is used to synthesise the array’s focusing and steering in post processing. However, the FMC data acquisition method is based on concepts for transducer-based phased arrays that assume a fixed geometry of instrumentation and capture the Full Matrix irrespective of the usefulness and contribution of the signals to the final image. This is a major limitation when data acquisition speed and data volume is important. In order to overcome this obstacle a fundamental change in the data acquisition methodology for ultrasonic imaging is required. The work presented here introduces a novel data acquisition method, the Selective Matrix Capture (SMC), that can adapt the array geometry during data acquisition, to the demands of the inspected structure, such as the defects encountered. The adaptive data acquisition method is enabled by the use of Laser Induced Phased Arrays (LIPAs).LIPAs use laser ultrasonics to generate and detect ultrasound by means of lasers. In a LIPA, the array is synthesised in post processing by recording laser ultrasound data from multiple generation and detection points on the surface of a component. The focusing and steering of the ultrasonic beam is done in post-processing by an&nbsp;imaging algorithm. The advantage is that laser ultrasonics is a remote and couplant-free technique addressing the current NDE challenges of inspection of complex structures and under extreme environments. In addition, LIPAs provide superior ultrasonic imaging performance over conventional laser ultrasonic techniques because of the beam forming that is done in post processing, while operating in the non-ablative, non-destructive regime. LIPAs have elements made of light and they are highly reconfigurable with respect to element number and position, unlike their transducer-based counterparts. We have previously demonstrated high-resolution ultrasonic images of the interior of components using FMC and TFM. However, capturing the FMC requires long synthesis time due to signal averaging and mechanical laser scanning, compromising the application potential of LIPAs. Given that most components are defect free, significant time savings can be obtained by only acquiring high-fidelity data when a defect is indicated. The paper presents the Selective Matrix Capture that captures data more efficiently without a priori knowledge of the location of the defects, while still achieving the superior imaging quality provided by an FMC dataset. This is achieved by taking into consideration the generation and detection characteristics of laser ultrasonics and utilising the high flexibility of LIPAs. The SMC data acquisition method proposed here, consists o

Adaptive Data Acquisition for Fast Ultrasonic Imaging Using Laser Induced Phased Arrays

Cementing operation is an indispensable part of the well completion in the petroleum industry. The cement bond quality has significant influence on the life, the production safety, and the overall benefits of an oil or gas well. Acoustic logging, as one of the important techniques for the cement bond evaluation, mainly uses the amplitude or attenuation of the acoustic waves propagating along the casing to investigate the bond quality of cement sheath with the casing (first interface) and the formation (second interface). Therefore, this paper uses an analytical wave separation method to calculate the detailed propagation characteristics of casing wave in cased borehold wavefield, analyzing the characteristics of casing wave and P-wave of the formation in the wavefield with the change of cement density and microring thickness, respectively, which is achieved by decomposing the full wave of the sound field into contributions from singular points (including branch points and poles) in the wavenumber domain. The results show that high-amplitude casing waves will still appear in well-bonded cased borehole in the case of low-density cement. Therefore, the impact of cement strength should be considered when evaluating cementing quality; the first wave in the first interface unbonded cased borehole are all casing waves in the case of conventional cement, and with the increase of the thickness of the microring, the amplitude of the casing wave increases sharply. This result is consistent with the actual phenomenon.

Calculation and Characteristic Research of Partial Waves in Cased Borehole

State of the art wireless telecommunication devices are operating in the (low) frequency GHz regime. They pick up broadband electromagnetic signals, which are band-pass filtered to comply with a designated frequency band. This is usually achieved by a filter-stage, based on several highly efficient electroacoustic devices, i.e., bulk-acoustic wave (BAW) filters. The performance of these BAW-filters is influenced by the acoustic losses of its constituent materials. Knowing the acoustic losses of these materials allows filter manufacturers to better simulate and optimize their devices. Here, we present a method for the determination of acoustic losses of individual materials at frequencies around 2GHz. It is based on measuring the quality factor of Lamb-wave resonances in plates with thicknesses of around 1µm with a frequency domain laser-ultrasound setup.In the dispersion curves f(k) of plate-like structures points with zero-group velocity (i.e., with a vanishing slope) occur at certain combinations of frequency and wavenumber. Two types are being distinguished: Points with a vanishing wavenumber (infinite wavelength), called thickness resonances or cut-offs, and such with a finite wavenumber (wavelength) which are usually denoted as zero group velocity resonances (ZGVs). Due to the hampered energy transport, both appear as dominant peaks in local frequency response spectra. The frequency position of the plate-resonances has been successfully used to characterize the thickness and elastic properties of plates. The shape of the resonance-peak is associated with the temporal decay of the resonances, which is composed of a power-law contribution due to transient spatial spreading of the mode, and an exponential decay, associated with the material damping. Thus, the shape (width) of the peaks in the frequency domain can be used to determine the intrinsic acoustic attenuation at a frequency determined by the peak position.Two-approaches for the determination of the longitudinal attenuation coefficient are being presented. One is based on the direct measurement of longitudinal thickness resonances in plates with different thicknesses, i.e., different resonance frequencies. The second uses two ZGV-resonances, which are governed by a mixture of longitudinal and transverse wave motion. A method is shown, to disentangle their damping contributions to obtain pure longitudinal and transvers attenuation coefficients in isotropic materials. For both cases, signal-processing methods for the compensation of the power-law contribution are shown. Experimental results are presented for the materials Aluminum and Tungsten.

Determination of the Acoustic Attenuation in the Ghz-Regime Using Zero-Group Velocity Plate-Resonances

Ultrasonic phased arrays have seen a dramatic increase in their use for non-destructive testing. The data from one-dimensional (1D) phased arrays are used to produce two-dimensional (2D), cross-sectional images, whereas the data from two-dimensional phased arrays generate three-dimensional (3D) images (volumetric imaging), thus providing more information on defects. However, transducer-based phased arrays fail to operate at the high temperatures and harsh environments offered by methods such as welding and additive manufacturing. Laser Induced Phased Arrays (LIPAs) can be used in such hostile environments due to the remote mode of operation associated with laser ultrasonics. Contrary to transducer-based phased arrays, LIPAs are synthesized in post-processing. LIPAs implement one laser to generate ultrasound and another laser to detect the surface displacements. The generation and detection laser beams are scanned on the surface of the sample to capture the full matrix (FMC). In this work, 2D LIPAs are synthesized in the non-destructive thermoelastic regime using a 7 ns pulsed Nd:YAG laser and a 532 nm continuous wave laser to image defects of varying sizes at different depths inside an aluminium and a steel sample. The acquired data is processed using the Total Focusing Method (TFM) algorithm to obtain a volumetric image representing the interior of the sample. A 3D finite element (FE) model is also developed to support the experiments.

Remote, Volumetric Ultrasonic Imaging of Defects Using Two-Dimensional Laser Induced Phased Arrays

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.