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  • Conference paper
    Huthwaite P, Lowe M, Cawley P, 2015,

    Guided Wave Tomography Performance Analysis

    , 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: American Institute of Physics (AIP), ISSN: 1551-7616

    Quantifying wall loss caused by corrosion is a significant challenge for the petrochemical industry. Corrosion commonly occurs at pipe supports, where surface access for inspection is limited. Guided wave tomography is pursued as a solution to this: guided waves are transmitted through the region of interest from an array, and tomographic reconstruction techniques are applied to the measured signals in order to produce a map of thickness. There are many parameters in the system which can affect the performance; this paper investigates how the accuracy varies as defect width and depth, operating frequency and guided wave mode are all changed. For the S0 mode, the best performance was seen around 170kHz on the 10mm plate, with poor performance seen at almost all other frequencies. A0 showed better performance across a broad range of frequencies, with resolution improving with frequency as the wavelength reduced. However, it was shown that the resolution limit did drop relative to the wavelength, limiting the performance at high frequencies slightly.
  • Conference paper
    Ewert U, Tschaikner M, Hohendorf S, Bellon C, Haith MI, Huthwaite P, Lowe MJSet al., 2015,

    Corrosion Monitoring with Tangential Radiography and Limited View Computed Tomography

    , 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: American Institute of Physics (AIP), ISSN: 1551-7616

    Accurate and reliable detection of subsea pipeline corrosion is required in order to verify the integrity of the pipeline. A laboratory trial was conducted with a representative pipe sample. The accurate measurement of the wall thickness and corrosion was performed with high energy X-rays and a digital detector array. A 7.5 MV betatron was used to penetrate a stepped pipe and a welded test pipe of 3 m length and 327 mm outer diameter, with different artificial corrosion areas in the 24 mm thick steel wall. The radiographs were taken with a 40 x 40 cm² digital detector array, which was not large enough to cover the complete pipe diameter after magnification. A C-arm based geometry was tested to evaluate the potential for automated inspection in field. The primary goal was the accurate measurement of wall thickness conforming to the standard. The same geometry was used to explore the ability of a C-arm based scanner in asymmetric mode for computed tomography (CT) measurement, taking projections covering only two thirds of the pipe diameter. The technique was optimized with the modelling software aRTist. A full volume of the pipe was reconstructed and the CT data set was used for reverse engineering, providing a CAD file for further aRTist simulations to explore the technique for subsea inspections.
  • Conference paper
    Haith MI, Ewert U, Hohendorf S, Bellon C, Deresch A, Huthwaite P, Lowe MJS, Zscherpel Uet al., 2015,

    Modelling Based Radiography for NDE of Subsea Pipelines

    , 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: American Institute of Physics (AIP), ISSN: 1551-7616

    This work presents the use of limited experimental measurements to develop a set of calibrated simulation parameters that can then be used for reliable simulation of subsea pipeline inspections. The modelling software aRTist is used as the simulation tool, and the calibration is through comparison with experimental images of a well characterised sample in a water tank. Image quality parameters such as signal-to-noise ratio, contrast and basic spatial resolution are compared with the aim of matching simulated values to experimental results. Currently the model is partially calibrated, with signal-to-noise ratio successfully matched while differences are still found in contrast-to-noise ratio comparisons. This means that measurements depending on absolute intensity are not accurate enough in the simulation at this stage. However, the simulation is found to be accurate for wall thickness measurements in tangential images, which are not based on absolute intensity, with simulated and experimental cases producing similar results
  • Conference paper
    Van Pamel A, Huthwaite P, Brett CR, Lowe MJSet al., 2015,

    Finite Element Modelling of Wave Propagation in Highly Scattering Materials

    , 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: American Institute of Physics (AIP), ISSN: 1551-7616

    Ultrasonic inspection of highly scattering materials presents challenges for industry. This article describes a Finite Element modelling methodology to simulate wave propagation within polycrystalline materials. Concerns are answered regarding its required mesh sampling and ability to capture the complex scattering physics. It is shown that grain scattering phenomena are closely reproduced across a range of scattering regimes. The procedure is subsequently applied to investigate the optimal configuration of an array inspecting such a material. It is found that in certain situations, separating emitter and receiver can be advantageous as this reduces the received backscatter.
  • Journal article
    Leinov E, Lowe MJS, Cawley P, 2015,

    Investigation of guided wave propagation and attenuation in pipe buried in sand

    , Journal of Sound and Vibration, Vol: 347, Pages: 96-114, ISSN: 0022-460X

    Long-range guided wave testing is a well-established method for detection of corrosion defects in pipelines. The method is currently used routinely for above ground pipelines in a variety of industries, e.g. petrochemical and energy. When the method is applied to pipes buried in soil, test ranges tend to be significantly compromised and unpredictable due to attenuation of the guided wave resulting from energy leakage into the embedding soil. The attenuation characteristics of guided wave propagation in an 8 in. pipe buried in sand are investigated using a laboratory full-scale experimental rig and model predictions. We report measurements of attenuation of the T(0,1) and L(0,2) guided wave modes over a range of sand conditions, including loose, compacted, mechanically compacted, water saturated and drained. Attenuation values are found to be in the range of 1.65–5.5 dB/m and 0.98–3.2 dB/m for the torsional and longitudinal modes, respectively, over the frequency of 11–34 kHz. The application of overburden pressure modifies the compaction of the sand and increases the attenuation. Mechanical compaction of the sand yields similar attenuation values to those obtained with applied overburden pressure. The attenuation decreases in the fully water-saturated sand, and increases in drained sand to values comparable with those obtained for compacted sand. Attenuation measurements are compared with Disperse software model predictions and confirm that the attenuation phenomenon in buried pipes is essentially governed by the bulk shear velocity in the sand. The attenuation behaviour of the torsional guided wave mode is found not to be captured by a uniform soil model; comparison with predictions obtained with the Disperse software suggest that this is likely to be due to a layer of sand adhering to the surface of the pipe.
  • Journal article
    Seher M, Huthwaite P, Lowe MJS, Nagy PBet al., 2015,

    Model-Based Design of Low Frequency Lamb Wave EMATs for Mode Selectivity

    , Journal of Nondestructive Evaluation, Vol: 34, ISSN: 1573-4862

    A low-frequency, omni-directional A0 Lamb wave ElectroMagnetic Acoustic Transducer (EMAT) is developed for applications in guided wave tomography, operating at 50 kHz on a 10 mm thick steel plate. The key objective is to excite an acceptably pure A0 wave mode in relation to the S0 mode, which can also be present at this operating point and is desired to be suppressed by approximately 30 dB. For that, a parametric Finite Element (FE) model of the design concept is implemented in a commercially available FE software, where the bias magnetic field is calculated initially, then combined with the eddy current caused by the induction coil to produce a force. A numerical optimization process employing a genetic algorithm is set up and the EMAT design is optimized to yield an improved A0 mode selectivity. The parameters subjected to optimization are the magnet diameter and the magnet lift-off, which control the direction of the exciting force in the skin depth layer and therefore the mode selectivity. Although there are three possible electromagnetic acoustic interaction mechanisms, the optimisation considers only the Lorentz force, as its performance surface contains a clear optimum and from the optimised design a physical prototype is built. The FE model is validated against measurements on an aluminium plate for the Lorentz force excitation mechanism and on a steel plate for both the Lorentz and magnetisation force. For the steel plate, it is found that only considering the Lorentz force leads to a significant overestimation of the mode selectivity, as the S0 amplitude is underestimated by the Lorentz force, but the A0 amplitude remains mainly uninfluenced. Further, it has been found that additionally including the magnetisation force into the optimisation leads to a better mode selectivity, however, the optimisation drives the optimum to a minimum magnet diameter and therefore reduces the EMAT sensitivity. In a numerical study robustness is shown for fair
  • Journal article
    Lan B, lowe M, dunne F, 2015,

    A generalized spherical harmonic deconvolution to obtain texture of cubic materials from ultrasonic wave speed

    , Journal of the Mechanics and Physics of Solids, Vol: 83, Pages: 221-242, ISSN: 0022-5096

    In this paper, the spherical harmonic convolution approach for HCP materials (Lan et al., 2015) is extended into a generalised form for the principal purpose of bulk texture determination in cubic polycrystals from ultrasonic wave speed measurements. It is demonstrated that the wave speed function of a general single crystal convolves with the polycrystal Orientation Distribution Function (ODF) to make the resultant polycrystal wave speed function such that when the three functions are expressed in harmonic expansions, the coefficients of any one function may be determined from the coefficients of the other two. All three Euler angles are taken into account in the description of the ODF such that the theorem applies for all general crystal systems.The forward problem of predicting polycrystal wave speed with knowledge of single crystal properties and the ODF is solved for all general cases, with validation carried out on cubic textures showing strong sensitivity to texture and excellent quantitative accuracy in predicted wave speed amplitudes. Importantly, it is also revealed by the theorem that the cubic structure is one of only two crystal systems (the other being HCP) whose orientation distributions can be inversely determined from polycrystal wave velocities by virtue of their respective crystal symmetries. Proof of principle is then established by recovering the ODFs of representative cubic textures solely from the wave velocities generated from a computational model using these texture inputs, and excellent accuracies are achieved in the recovered ODF coefficients as well as the resultant pole figures. Hence the methodology is argued to provide a powerful technique for wave propagation studies and bulk texture measurement in cubic polycrystals and beyond.Keywords Texture; Generalised spherical convolution; Ultrasound; Cubic polycrystals
  • Journal article
    Shi F, Choi W, Lowe MJS, Skelton EA, Craster RVet al., 2015,

    The validity of Kirchhoff theory for scattering of elastic waves from rough surfaces

    , PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 471, ISSN: 1364-5021
  • Journal article
    Huthwaite P, Seher M, 2015,

    Robust Helical Path Separation for Thickness Mapping of Pipes by Guided Wave Tomography

    , IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, Vol: 62, Pages: 927-938, ISSN: 1525-8955

    Pipe wall loss caused by corrosion can be quantifiedacross an area by transmitting guided Lamb waves throughthe region and measuring the resulting signals. Typically thedispersive relationship for these waves, which means thatwave velocity is a known function of thickness, is exploited,enabling the wall thickness to be determined from a velocityreconstruction. The accuracy and quality of this reconstructionis commonly limited by the angle of view available from thetransducer arrays. These arrays are often attached as a pairof ring arrays on either side of the inspected region, and dueto the cylindrical nature of the pipe, waves are able to travelin an infinite number of helical paths between any two transducers.The first arrivals can be separated relatively easily bytime gating, but by using just these components the angle ofview is severely restricted. To improve the viewing angle, it isnecessary to separate the wavepackets. This paper provides anoutline of a separation approach: initially the waves are backpropagatedto their source to align the different signals, then afiltering technique is applied to select the desired components.The technique is applied to experimental data and demonstratedto robustly separate the signals
  • Journal article
    Quintanilla FH, Lowe MJS, Craster RV, 2015,

    Modeling guided elastic waves in generally anisotropic media using a spectral collocation method

    , Journal of the Acoustical Society of America, Vol: 137, Pages: 1180-1194, ISSN: 0001-4966

    Guided waves are now well established for some applications in the non-destructive evaluation of structures and offer potential for deployment in a vast array of other cases. For their development, it is important to have reliable and accurate information about the modes that propagate for particular waveguide structures. Essential information that informs choices of mode transducer, operating frequencies, and interpretation of signals, among other issues, is provided by the dispersion curves of different modes within various combinations of geometries and materials. In this paper a spectral collocation method is successfully used to handle the more complicated and realistic waveguide problems that are required in non-destructive evaluation; many pitfalls and limitations found in root-finding routines based on the partial wave method are overcome by using this approach. The general cases presented cover anisotropic homogeneous perfectly elastic materials in flat and cylindrical geometry. Non-destructive evaluation applications include complex waveguide structures, such as single or multi-layered fiber composites, lined, bonded and buried structures. For this reason, arbitrarily multi-layered systems with both solid and fluid layers are also addressed as well as the implementation of interface models of imperfect boundary conditions between layers.
  • Conference paper
    Van Pamel A, Huthwaite P, Brett CR, Lowe MJSet al., 2015,

    A Finite Element Model Investigation of Ultrasonic Array Performance for Inspecting Polycrystalline Materials

    , 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 1007-1014, ISSN: 0094-243X
  • Conference paper
    Pettit JR, Walker AE, Lowe MJS, 2015,

    Modelling NDE Pulse-Echo inspection Of Misorientated Planar Rough Defects Using An Elastic Finite Element Method

    , 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 1730-1737, ISSN: 0094-243X
  • Conference paper
    Huthwaite P, Shi F, Van Pamel A, Lowe MJSet al., 2015,

    High-Speed GPU-Based Finite Element Simulations for NDT

    , 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 1815-1819, ISSN: 0094-243X
  • Conference paper
    Shi F, Choi W, Skelton E, Lowe M, Craster Ret al., 2015,

    Investigation of the Validity of the Elastic Kirchhoff Approximation for Rough Cracks Using a Finite Element Approach

    , 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 1722-1729, ISSN: 0094-243X
  • Conference paper
    Van Pamel A, Brett CR, Lowe MJS, 2015,

    An Initial Investigation into Pseudo-Coloring for Ultrasonic NDE of Polycrystalline Materials

    , 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 1031-1036, ISSN: 0094-243X
  • Conference paper
    Pettitt JR, Walker A, Lowe MJS, 2015,

    An optimised stiffness reduction method for simulating infinite elastic space using commercial Finite Elements codes

    , 13th Anglo-French Physical Acoustics Conference (AFPAC), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
  • Conference paper
    Leinov E, Cawley P, Lowe MJS, 2015,

    Guided Wave Attenuation in Pipes Buried in Sand

    , 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 227-236, ISSN: 0094-243X
  • Conference paper
    Corcoran J, Davies CM, Nagy PB, Cawley Pet al., 2015,

    Potential Drop Strain Measurement for Creep Monitoring

    , 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 917-925, ISSN: 0094-243X
  • Conference paper
    Seher M, Huthwaite P, Lowe M, Cawley Pet al., 2015,

    Experimental Study of A0 Lamb Wave Tomography

    , 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 245-253, ISSN: 0094-243X
  • Conference paper
    Quintanilla FH, Lowe M, Craster R, 2015,

    Dispersion Curves for Guided Elastic Waves in Multilayered Anisotropic Media Generated with the Spectral Method

    , 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 739-745, ISSN: 0094-243X

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