Publications
520 results found
Li Z, Jarvis R, Nagy PB, et al., 2017, Experimental and simulation methods to study the Magnetic Tomography Method (MTM) for pipe defect detection, NDT & E INTERNATIONAL, Vol: 92, Pages: 59-66, ISSN: 0963-8695
Li Z, Dixon S, Cawley P, et al., 2017, Experimental studies of the magneto-mechanical memory (MMM) technique using permanently installed magnetic sensor arrays, NDT & E INTERNATIONAL, Vol: 92, Pages: 136-148, ISSN: 0963-8695
Heinlein S, Cawley P, Vogt TK, 2017, Reflection of torsional T(0,1) guided waves from defects in pipe bends, NDT and E International, Vol: 93, Pages: 57-63, ISSN: 0963-8695
This paper investigates the reflection of the torsional T(0,1) mode from defects in pipe bends. The effect of varying circumferential and angular position along the pipe bend, as well as the influence of the bend radius, is investigated via 3D finite element simulations. The results show that the reflection expected from a small defect varies significantly with position, the minimum reflection coefficient being about 10% of that from a comparable defect in a straight pipe, while maxima of around four times the straight pipe value are seen. The areas of low detectability are mainly found on the bend intrados and those of high detectability close to its extrados; similar effects are seen in bends with radii varying from one to twenty pipe diameters. It is shown that the reflection from a defect at a given location is roughly proportional to the square of the von Mises stress produced by the transmitted wave at that position. This holds for defects such as circumferential cracks, the detailed subject of this investigation, and is also expected to be valid for corrosion patches; it will not hold for axial cracks. The results explain the low reflection seen from a simulated corrosion defect at a bend in a previous investigation.
Liu Y, Chang L, van Pamel A, et al., 2017, Feasibility and reliability of grain noise suppression in monitoring of highly scattering materials, Journal of Nondestructive Evaluation, Vol: 36, ISSN: 1573-4862
A feasibility study on grain noise suppression using baseline subtraction is presented in this paper. Monitoring is usually done with permanently installed transducers but this is not always possible; here instead monitoring is conducted by carrying out repeat C-scans and the feasibility of grain noise suppression by subtracting A-scans extracted from the C-scans is investigated. The success of this technique depends on the ability to reproduce the same conditions for each scan, including a consistent stand-off, angle, and lateral position of the transducer relative to the testpiece. The significance of errors are illustrated and a 3D cross correlation is used which enables the same lateral position to be located within successive C-scans. The experimental results show that a noise reduction of around 15 dB is obtained after baseline subtraction, which will significantly improve the defect detection sensitivity. In practice however, successive C-scans may be conducted at different temperatures and with different transducers of similar specifications but a varying frequency response. Compensation techniques to reduce the impact of such variations are then presented and their effectiveness is verified experimentally. It is shown that it is feasible to obtain an overall improvement of around 10 dB in the signal to noise ratio via baseline subtraction, where a temperature difference of up to 10 ∘C and a peak frequency shift of as much as ±250 kHz from a baseline value of around 7 MHz can be tolerated. However, this improvement was obtained in laboratory conditions with no changes to the surface of the specimen due to oxidation or corrosion. It is shown that differences in temperature and transducer frequency response are more difficult to compensate for than changes in test geometry and position.
Jarvis R, Cawley P, Nagy P, 2017, Performance evaluation of a magnetic field measurement NDE technique using a model assisted probability of detection framework, NDT & E International, Vol: 91, Pages: 61-70, ISSN: 0963-8695
Receiver Operating Characteristics (ROC) are a powerful tool used to evaluate the performance of NDE methods; however, the need to manufacture and scan many test pieces with realistic defects means that they are expensive and time-consuming to produce. Advances in computational power now mean that it is possible to use numerical models to greatly increase the efficiency of producing ROC for practical applications. A Model Assisted Probability of Detection (MAPOD) framework has been developed to predict the performance of magnetic field measurement NDE techniques. The MAPOD method is used to predict the performance of a promising new technique relying on the deflection of a current injected into a pipe at remote locations, and measurement of the resulting magnetic field perturbations due to defects. A significant proportion of pipes cannot be inspected by pigging methods, and external inspection often requires complete coating removal; therefore, an NDE method that functions outside pipe coatings and cladding is attractive. In this method, changes in the radial and axial components of the field are measured and attributed to defects, but a strong azimuthal component means that misalignment can give significant apparent radial and axial signals due to the azimuthal field apparently having a component in these directions. This requires that the second-order gradient of the magnetic field be measured to maximise sensitivity. Fluctuations in the sensitivity and orientation of the gradiometer during the scan are expected to determine the maximum sensitivity of the technique in most practical applications; however, the flexibility of the framework allows performance to be rapidly predicted and quantified for many test scenarios. Results suggest good detection performance for defects greater than 15% of the wall thickness (T = 7.1 mm) in a 6″ pipe with 2 A (200 A/m2) current injected when measuring above typical insulation thickness (25–50 mm).
Corcoran J, Nagy PB, Cawley P, 2017, Monitoring creep damage at a weld using a potential drop technique, INTERNATIONAL JOURNAL OF PRESSURE VESSELS AND PIPING, Vol: 153, Pages: 15-25, ISSN: 0308-0161
Liu C, Dobson J, Cawley P, 2017, Efficient generation of receiver operating characteristics for the evaluation of damage detection in practical structural health monitoring applications, Proceedings of the Royal Society of London. Series A, Mathematical and physical sciences, Vol: 473, Pages: 1-26, ISSN: 0080-4630
Permanently installed guided wave monitoring systems are attractive for monitoring large structures. By frequently interrogating the test structure over a long period of time, such systems have the potential to detect defects much earlier than with conventional one-off inspection, and reduce the time and labour cost involved. However, for the systems to be accepted under real operational conditions, their damage detection performance needs to be evaluated in these practical settings. The receiver operating characteristic (ROC) is an established performance metric for one-off inspections, but the generation of the ROC requires many test structures with realistic damage growth at different locations and different environmental conditions, and this is often impractical. In this paper, we propose an evaluation framework using experimental data collected over multiple environmental cycles on an undamaged structure with synthetic damage signatures added by superposition. Recent advances in computation power enable examples covering a wide range of practical scenarios to be generated, and for multiple cases of each scenario to be tested so that the statistics of the performance can be evaluated. The proposed methodology has been demonstrated using data collected from a laboratory pipe specimen over many temperature cycles, superposed with damage signatures predicted for a flat-bottom hole growing at different rates at various locations. Three damage detection schemes, conventional baseline subtraction, singular value decomposition (SVD) and independent component analysis (ICA), have been evaluated. It has been shown that in all cases, the component methods perform significantly better than the residual method, with ICA generally the better of the two. The results have been validated using experimental data monitoring a pipe in which a flat-bottom hole was drilled and enlarged over successive temperature cycles. The methodology can be used to evaluate the performance of an
Cawley P, dobson J, 2017, The scattering of torsional guided waves from Gaussian rough surfaces in pipework, Journal of the Acoustical Society of America, Vol: 141, Pages: 1852-1861, ISSN: 0001-4966
In older sections of industrial pipework there are often regions of general corrosion with a Gaussian thickness distribution. During guided wave inspection this corrosion causes an increase in the background noise and a significant attenuation of the inspection wave. These effects are investigated in this paper through finite element modelling of the interaction of torsional guided waves with rough surfaces in pipes. Pipes of different diameter and rough surface profile are modelled and it is found that the attenuation of waves is explained by significant mode conversion and scattering within the rough surface. This mode conversion is greatest when the non–axisymmetric modes to which energy is scattered are close to their cut-off frequency or when the ratio of surface correlation length to wavelength is around 0.2-0.25. Mode conversion increases with increasing surface roughness and is a strong function of frequency-diameter product, with larger pipes causing more mode conversion. When this mode conversion occurs the energy is lost mostly to those waves with a displacement profile closest to the original torsional inspection wave. Resulting attenuation of the inspection signal can be severe; for example a mean wall thickness loss of 28% can cause 2.7 dB/m attenuation in a pulse-echo configuration.
Leinov E, Lowe MJS, Cawley P, 2016, Investigation of guided wave propagation in pipes fully- and partially-embedded in concrete, The Journal of the Acoustical Society of America, Vol: 140, ISSN: 1520-8524
The application of long-range guided-wave testing to pipes embedded in concrete results in unpredictable test-ranges. The influence of the circumferential extent of the embedding-concrete around a steel pipe on the guided wave propagation is investigated. An analytical model is used to study the axisymmetric fully embedded pipe case, while explicit finite-element and semi-analytical finite-element simulations are utilised to investigate a partially embedded pipe. Model predictions and simulations are compared with full-scale guided-wave tests. The transmission-loss of the T(0,1)-mode in an 8 in. steel pipe fully embedded over an axial length of 0.4 m is found to be in the range of 32–36 dB while it reduces by a factor of 5 when only 50% of the circumference is embedded. The transmission-loss in a fully embedded pipe is mainly due to attenuation in the embedded section while in a partially embedded pipe it depend strongly on the extent of mode-conversion at entry to the embedded-section; low loss modes with energy concentrated in the region of the circumference not-covered with concrete have been identified. The results show that in a fully embedded pipe, inspection beyond a short distance will not be possible, whereas when the concrete is debonded over a fraction of the pipe circumference, inspection of substantially longer lengths may be possible.
Li Z, Dixon S, Cawley P, et al., 2016, Study of Metal Magnetic Memory (MMM) Technique Using Permanently Installed Magnetic Sensor Arrays, 43rd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, ISSN: 0094-243X
Jarvis R, Cawley P, Nagy PB, 2016, Current deflection NDE for the inspection and monitoring of pipes, NDT & E International, Vol: 81, Pages: 46-59, ISSN: 0963-8695
Routine inspection of oil and gas pipes for time dependent degradation is essential. Pipelines are most commonly inspected using In-Line Inspection (ILI), however restrictions from pipe geometry, features or flow rate can prevent its use. Facility pipework rarely facilitates ILI, and external inspection often warrants the undesirable removal of the pipe insulation and cladding. This work investigates the applicability of a current deflection non-destructive evaluation technique for both the detection and growth monitoring of defects, particularly focusing on corrosion. Magnetic sensors are used to monitor variations in the spatial distribution of the induced magnetic flux density outside a pipe that arise from deflection of an injected electric current around inner or outer wall defects. An array of orthogonal magnetoresistive sensors has been used to measure the magnetic flux density surrounding six-inch schedule 40 seamless and welded carbon steel and austenitic steel pipes. The measurements were stable and repeatable to the order of 100 pT which suggests that the defect detection or growth monitoring of corrosion-type defects may be possible with a few amps of injected current when measurements are taken at around 50 mm lift-off. The sensitivity of the technique is dependent on factors including defect geometry, sensor lift-off, bends, variations in nominal pipe geometry or material properties, and the presence of ferromagnetic objects, each of which were investigated using either experiment or a validated finite element model.
Corcoran J, Hooper P, Davies C, et al., 2016, Creep strain measurement using a potential drop technique, International Journal of Mechanical Sciences, Vol: 110, Pages: 190-200, ISSN: 0020-7403
This paper will demonstrate the use of a potential drop sensor to monitor strain. In particular, the suitability of the technique to high temperature or harsh environment applications presents an opportunity for monitoring strain in components operating under creep conditions. Monitoring creep damage in power station components is a long standing technological challenge to the non-destructive evaluation community. It is well established in the literature that strain rate serves as an excellent indicator of the progress of creep damage and can be used for remnant life calculations. To facilitate the use of such strain rate based evaluation methods, a permanently installed, strain sensitive, potential drop technique has been developed. The technique has very simple and robust hardware lending itself to use at high temperatures or in harsh environments. Strain inversions are presented and demonstrated experimentally; a room temperature, plastic deformation experiment is used for validation and additionally an accelerated creep test demonstrates operation at high temperature (600 °C+). Excellent agreement is shown between potential drop inverted strain and control measurements.
Leinov E, Lowe MJS, Cawley P, 2016, Ultrasonic isolation of buried pipes, Journal of Sound and Vibration, Vol: 363, Pages: 225-239, ISSN: 0022-460X
Long-range guided wave testing (GWT) is used routinely for the monitoring and detection of corrosion defects in above ground pipelines. The GWT test range in buried, coated pipelines is greatly reduced compared to above ground configurations due to energy leakage into the embedding soil. In this paper, the effect of pipe coatings on the guided wave attenuation is investigated with the aim of increasing test ranges for buried pipelines. The attenuation of the T(0,1) and L(0,2) guided wave modes is measured using a full-scale experimental apparatus in a fusion-bonded epoxy (FBE)-coated 8 in. pipe, buried in loose and compacted sand. Tests are performed over a frequency range typically used in GWT of 10–35 kHz and compared with model predictions. It is shown that the application of a low impedance coating between the FBE layer and the sand effectively decouples the influence of the sand on the ultrasound leakage from the buried pipe. Ultrasonic isolation of a buried pipe is demonstrated by coating the pipe with a Polyethylene (PE)-foam layer that has a smaller impedance than both the pipe and sand, and has the ability to withstand the overburden load from the sand. The measured attenuation in the buried PE-foam-FBE-coated pipe is found to be substantially reduced, in the range of 0.3–1.2 dB m⁻¹ for loose and compacted sand conditions, compared to measured attenuation of 1.7–4.7 dB m⁻¹ in the buried FBE-coated pipe without the PE-foam. The acoustic properties of the PE-foam are measured independently using ultrasonic interferometry and incorporated into model predictions of guided wave propagation in buried coated pipe. Good agreement is found between the experimental measurements and model predictions. The attenuation exhibits periodic peaks in the frequency domain corresponding to the through-thickness resonance frequencies of the coating layer. The large reduction in guided wave attenuation for PE-coated pipes would lead to greatly increas
Khalili P, Cawley P, 2016, Excitation of single-mode Lamb waves at high-frequency-thickness products, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol: 63, Pages: 303-312, ISSN: 0885-3010
Guided wave inspection is used extensively in petrochemical plants to check for defects such as corrosion. Long-range low-frequency inspection can be used to detect relatively large defects, while higher frequency inspection provides improved sensitivity to small defects, but the presence of multiple dispersive modes makes it difficult to implement. This paper investigates the possibility of exciting a single-mode Lamb wave with low dispersion at a frequency thickness of around 20 MHz-mm. It is shown by finite element (FE) analysis backed up by experiments that a signal dominated by the A1 mode can be generated, even in a region where many modes have similar phase velocities. The A1 mode has relatively little motion at the plate surface which means that only a small reflection is generated at features such as T-joints; this is verified numerically. It is also expected that it will be relatively unaffected by surface roughness or attenuative coatings. These features are very similar to those of the higher order mode cluster (HOMC) reported by other authors, and it is shown that the A1 mode shape is very similar to the deflected shape reported in HOMC.
Liu C, Cawley P, 2016, Practical guided wave SHM of pipes-processing multiple data sets to give reliable defect detection, Pages: 1236-1244
Histori cally, most guided wave testing has been done on a one-off test (NDT) basis . However, permanently install ed systems ar e now commonly used, giving the oppor tuni ty to move from NDT to SHM. In conventional SHM, damage is detected by subtracting a measur ement from a baseline r ecord, after compensating for any temperatur e di ffer ence between the tests . However, the temperatur e compensation methods cannot per fectly r emove the benign variations produced by compl ex environmental and operational condi tions (EOCs), l eaving r esidual noise that can mask the damage signal. Component analysis methods such as singular value decomposi tion (SVD) and Independent Component Analysis (ICA) operating on mul tipl e data sets have the potential to improve the sensi tivi ty and r eliabili ty of defect detection. In this paper, we evaluate the SHM per formance on a syntheti c dataset that contains the superposi tion of experimental guided wave r ecords coll ected on a test pipe during temperatur e cycling, and computationally generated damage signals at various locations . This synthesis process enabl es us to investigate the per formance of the methods under di ffer ent EOC and damage condi tions . We compute the r eceiver operating characteristi c (ROC) curves that plot the probabili ty of detection against the probabili ty of false alarm for di ffer ent damage growth rates and di ffer ent fr equency of measur ements using the SVD, ICA, and the conventional baseline-subtraction r esidual methods . The r esul ts pr esented her e show the methodology using the conventional baseline-subtraction method; the confer ence pr esentation will show the comparison wi th SVD and ICA. The r esul ts show that the sensi tivi ty of the SHM processing is an order of magni tude better than that typi cally obtained in one-off guided wave NDT, and defects can much mor e r eliably be detected at featur es such as welds. The ROC curves can effi ci ently be derived for an install ed SHM
Dobson, Cawley P, 2015, Independent Component Analysis for Improved Defect Detection in Guided Wave Monitoring, Proceedings of the Institution of Electrical Engineers, Vol: 104, Pages: 1620-1631, ISSN: 0020-3270
Guided wave sensors are widely used in a number of industries and have found particular application in the oil and gas industry for the inspection of pipework. Traditionally this type of sensor was used for one-off inspections, but in recent years there has been a move towards permanent installation of the sensor. This has enabled highly repeatable readings of the same section of pipe, potentially allowing improvements in defect detection and classification. This paper proposes a novel approach using independent component analysis to decompose repeat guided wave signals into constituent independent components. This separates the defect from coherent noise caused by changing environmental conditions, improving detectability. This paper demonstrates independent component analysis applied to guided wave signals from a range of industrial inspection scenarios. The analysis is performed on test data from pipe loops that have been subject to multiple temperature cycles both in undamaged and damaged states. In addition to processing data from experimental damaged conditions, simulated damage signals have been added to “undamaged” experimental data, so enabling multiple different damage scenarios to be investigated. The algorithm has also been used to process guided wave signals from finite element simulations of a pipe with distributed shallow general corrosion, within which there is a patch of severe corrosion. In all these scenarios, the independent component analysis algorithm was able to extract the defect signal, rejecting coherent noise.
Corcoran J, Nagy PB, Cawley P, 2015, Potential Drop Monitoring of Creep Damage at a Weld, 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: American Institute of Physics (AIP), ISSN: 1551-7616
Creep failure at welds will often be the life limiting factor for pressurised power station components, offering a site for local damage accumulation. Monitoring the creep state of welds will be of great value to power station management and potential drop monitoring may provide a useful tool. This paper provides a preliminary study of potential drop monitoring of creep damage at a weldment, suggesting a measurement arrangement for a previously documented quasi-DC technique that is well suited to the application. The industrial context of the problem of creep damage at a weldment is explored, together with a numerical simulation of the effect of cracking, finally, a cross-weld accelerated creep test demonstrating the promise of the technique is presented.
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.
Leinov E, Cawley P, Lowe MJS, 2015, Guided Wave Attenuation in Coated Pipes Buried in Sand, 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: American Institute of Physics (AIP), ISSN: 1551-7616
Long-range guided wave testing (GWT) is routinely used for the monitoring and detection of corrosion defects in above ground pipelines in various industries. The GWT test range in buried, coated pipelines is greatly reduced compared to aboveground pipelines due to energy leakage into the embedding soil. In this study, we aim to increase test ranges for buried pipelines. The effect of pipe coatings on the T(0,1) and L(0,2) guided wave attenuation is investigated using a full-scale experimental apparatus and model predictions. Tests are performed on a fusion-bonded epoxy (FBE)-coated 8” pipe, buried in loose and compacted sand over a frequency range of 10-35 kHz. The application of a low impedance coating is shown to effectively decouple the influence of the sand on the ultrasound leakage from the buried pipe. We demonstrate ultrasonic isolation of a buried pipe by coating the pipe with a Polyethylene (PE)-foam layer that has a smaller impedance than both pipe and sand and the ability to withstand the overburden load from the sand. The measured attenuation in the buried PE-foam-FBE-coated pipe is substantially reduced, in the range of 0.3-1.2 dBm−1 for loose and compacted sand conditions, compared to buried FBE-coated pipe without the PE-foam, where the measured attenuation is in the range of 1.7-4.7 dBm−1. The acoustic properties of the PE-foam are measured independently using ultrasonic interferometry technique and used in model predictions of guided wave propagation in a buried coated pipe. Good agreement is found between the attenuation measurements and model predictions. The attenuation exhibits periodic peaks in the frequency domain corresponding to the through-thickness resonance frequencies of the coating layer. The large reduction in guided wave attenuation for PE-coated pipes would lead to greatly increased GWT test ranges, so such coatings would be attractive for new pipeline installations.
Jarvis R, Cawley P, Nagy PB, 2015, Current Deflection NDE for Pipeline Inspection and Monitoring, 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: American Institute of Physics (AIP), ISSN: 1551-7616
Failure of oil and gas pipelines can often be catastrophic, therefore routine inspection for time dependent degradation is essential. In-line inspection is the most common method used; however, this requires the insertion and retrieval of an inspection tool that is propelled by the fluid in the pipe and risks becoming stuck, so alternative methods must often be employed. This work investigates the applicability of a non-destructive evaluation technique for both the detection and growth monitoring of defects, particularly corrosion under insulation. This relies on injecting an electric current along the pipe and indirectly measuring the deflection of current around defects from perturbations in the orthogonal components of the induced magnetic flux density. An array of three orthogonally oriented anisotropic magnetoresistive sensors has been used to measure the magnetic flux density surrounding a 6’’ schedule-40 steel pipe carrying 2 A quasi-DC axial current. A finite element model has been developed that predicts the perturbations in magnetic flux density caused by current deflection which has been validated by experimental results. Measurements of the magnetic flux density at 50 mm lift-off from the pipe surface are stable and repeatable to the order of 100 pT which suggests that defect detection or monitoring growth of corrosion-type defects may be possible with a feasible magnitude of injected current. Magnetic signals are additionally incurred by changes in the wall thickness of the pipe due to manufacturing tolerances, and material property variations. If a monitoring scheme using baseline subtraction is employed then the sensitivity to defects can be improved while avoiding false calls.
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.
Dobson J, Cawley P, 2015, Independent Component Analysis for Improved Defect Detection in Guided Wave, 10th International Workshop on Structural Health Monitoring (IWSHM), Publisher: DESTECH PUBLICATIONS, INC, Pages: 1878-1885
Seher M, Huthwaite P, Lowe M, et 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
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Corcoran J, Davies CM, Nagy PB, et 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
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
Liu C, Dobson J, Cawley P, 2015, Practical Evaluation of SHM Damage Detection Under Complex Environmental Conditions Using Receiver Operating Characteristics, 10th International Workshop on Structural Health Monitoring (IWSHM), Publisher: DESTECH PUBLICATIONS, INC, Pages: 1949-1956
Escobar-Ruiz E, Wright DC, Collison IJ, et al., 2014, Reflection Phase Measurements for Ultrasonic NDE of Titanium Diffusion Bonds, JOURNAL OF NONDESTRUCTIVE EVALUATION, Vol: 33, Pages: 535-546, ISSN: 0195-9298
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Brierley N, Tippetts T, Cawley P, 2014, The computational enhancement of automated non-destructive inspection, INSIGHT, Vol: 56, Pages: 599-606, ISSN: 1354-2575
Pettit JR, Walker A, Cawley P, et al., 2014, A stiffness reduction method for efficient absorption of waves at boundaries for use in commercial Finite Element codes, Ultrasonics, Vol: 54, Pages: 1868-1879, ISSN: 0041-624X
Commercially available Finite Element packages are being used increasingly for modelling elastic wave propagation problems. Demand for improved capability has resulted in a drive to maximise the efficiency of the solver whilst maintaining a reliable solution. Modelling waves in unbound elastic media to high levels of accuracy presents a challenge for commercial packages, requiring the removal of unwanted reflections from model boundaries. For time domain explicit solvers, Absorbing Layers by Increasing Damping (ALID) have proven successful because they offer flexible application to modellers and, unlike the Perfectly Matched Layers (PMLs) approach, they are readily implemented in most commercial Finite Element software without requiring access to the source code. However, despite good overall performance, this technique requires the spatial model to extend significantly outside the domain of interest. Here, a Stiffness Reduction Method (SRM) has been developed that operates within a significantly reduced spatial domain. The technique is applied by altering the damping and stiffness matrices of the system, inducing decay of any incident wave. Absorbing region variables are expressed as a function of known model constants, helping to apply the technique to generic elastodynamic problems. The SRM has been shown to perform significantly better than ALID, with results confirmed by both numerical and analytical means.
Brierley N, Tippetts T, Cawley P, 2014, Data fusion for automated non-destructive inspection, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 470, Pages: 1-25, ISSN: 1364-5021
In industrial non-destructive evaluation (NDE), it is increasingly common for data acquisition to be automated, driving a recent substantial increase in the availability of data. The collected data need to be analysed, typically necessitating the painstaking manual labour of a skilled operator. Moreover, in automated NDE a region of an inspected component is typically interrogated several times, be it within a single data channel due to multiple probe passes, across several channels acquired simultaneously or over the course of repeated inspections. The systematic combination of these diverse readings is recognized to offer an opportunity to improve the reliability of the inspection, but is not achievable in a manual analysis. This paper describes a data-fusion-based software framework providing a partial automation capability, allowing component regions to be declared defect-free to a very high probability while readily identifying defect indications, thereby optimizing the use of the operator's time. The system is designed to applicable to a wide range of automated NDE scenarios, but the processing is exemplified using the industrial ultrasonic immersion inspection of aerospace turbine discs. Results obtained for industrial datasets demonstrate an orders-of-magnitude reduction in false-call rates, for a given probability of detection, achievable using the developed software system.
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