Showing papers on "Eddy-current testing published in 2002"
TL;DR: In this article, a new type of pulsed eddy current (PEC) sensor was designed for defect detection in aircraft lap-joint structures, which employs a new excitation circuit that requires no additional signal amplification and also reports compensation techniques that improve the sensing resolution and stability.
Abstract: This paper presents a new type of pulsed eddy current (PEC) sensor that has been designed for defect detection in aircraft lap-joint structures. The sensor employs a new excitation circuit that requires no additional signal amplification and the paper also reports compensation techniques that improve the sensing resolution and stability. A new hybrid feature of the peak value in time domain and the maximum frequency magnitude in frequency domain has been investigated. A test rig has been built and some results from aircraft samples are presented.
151 citations
TL;DR: In this article, closed-form expressions for the impedance of rectangular coils of rectangular cross-section located above a conducting half-space and for the eddy current density induced therein were provided.
Abstract: As for any other eddy current probe coil, the analysis of rectangular ones plays a vital role towards understanding their characteristics and performance. In this paper, closed-form expressions are provided both for the impedance of rectangular coils of rectangular cross-section located above a conducting half-space and for the eddy current density induced therein. The formulation is general and can be easily used for any coil shape.
110 citations
TL;DR: In this article, an optimum design method to determine the size of the magnet to maximize the magnetic flux leakage (MFL) signals in nondestructive testing (NDT) is described.
Abstract: In magnetic flux leakage (MFL)-type nondestructive testing (NDT) system, the sensitivity of MFL sensor depends on the change of the magnetic field, not just on the magnitude of the field. In this paper, the leakage parameter was defined to determine the operating point in saturation curves, and an optimum design method to determine the size of the magnet to maximize the MFL signals in NDT is described. For detecting the small depth defect, we also developed the back yoke sensor system. The sensitivity of the optimum sensor system is increased up to 200%. The computed MFL signals in the optimally designed system are verified by measurement using Hall sensors mounted on the six-legged PIG in an 8-in test pipe with defects. The rhombic defects could be successfully measured and identified from the weak defect signals.
87 citations
Patent•
16 Dec 2002TL;DR: In this paper, an eddy current coil was used to measure the gap gap between a rotating blade and a stationary component of a turbo-machine, including a tester and a coil.
Abstract: A system (90) for measuring the gap (16) between a rotating blade (14) and a stationary component (12) of a turbo-machine, including an eddy current coil (30) and an eddy current tester (91) The eddy current tester may excite the coil in a pulsed eddy current testing mode The coil is positioned in a stationary portion (12) of a turbo-machine traversed by a rotating blade and the eddy current tester is coupled to the eddy current coil to provide an indication responsive to a distance between the blade and the stationary portion as the blade traverses the position The coil may be mounted in a frangible ceramic pill (70) movably disposed in a housing (74) The coil is positioned near the turbine blade, the coil is excited with a voltage step function (120), and the response (122) of the coil to the step function is detected and processed to determine the proximity of the blade
50 citations
TL;DR: In this article, three finite-element formulations based on different definitions of current density are compared and errors due to the use of incomplete equations for current densities increase with frequency and conductor dimensions.
Abstract: Three finite-element formulations based on different definitions of current density are compared. Formulations I and II are based on incomplete equations for total and source current densities, respectively. Formulation III is based on a complete equation for source current density. To validate the third formulation, a one-dimensional test problem is solved analytically for the magnetic field intensity. The formulations are applied to a nondestructive testing example and a three-phase bus-bar example. Results show that errors due to the use of incomplete equations for current densities increase with frequency and conductor dimensions.
50 citations
TL;DR: In this article, an artificial neural network is presented for on-line eddy current testing of austenitic stainless steel welds, which is able to detect and characterize longitudinal and transverse surface-breaking notches, despite the presence of disturbing variables.
Abstract: An artificial neural network is presented for on-line eddy current testing of austenitic stainless steel welds. Time-domain parameters that are functions of digitized in-phase and quadrature components of probe impedance are used as input to the neural network and the network output, in depth units, is evaluated and displayed continuously. The neural network is trained to recognize disturbing variables such as variations in weld microstructure, lift-off and edge-effect as well as notches of different depth. The neural network is able to detect and characterize longitudinal and transverse surface-breaking notches, despite the presence of disturbing variables.
49 citations
TL;DR: In this article, the second-order vector potential formulation was used to solve the eddy current problem of a coil inside a conductive tube and in an offset position to it.
Abstract: By utilizing the second-order vector potential formulation we solve the eddy current problem of a coil inside a conductive tube and in an offset position to it. The study focuses on the derivation of a closed-form expression for the impedance change of the coil, which is used to calculate the signal produced by wobble in eddy current testing of tubes with bobbin coils.
43 citations
01 Jan 2002
TL;DR: The first edition of this book was published in 1996 to cover the principles, procedures, application, limitations and codes and standards of widely used non-destructive testing (NDT) techniques as mentioned in this paper.
Abstract: The first edition of this book was published in 1996 to cover the principles, procedures, application, limitations and codes and standards of widely used non-destructive testing (NDT) techniques. Techniques added to this second edition include neutron radiography, pulsed eddy current testing, low frequency eddy current testing, SQUID based eddy current testing and mechanical impedance analysis. There are 15 chapters: (1) Non-destructive testing: an introduction; (2) Visual Examination; (3) Liquid penetrant testing; (4) Magnetic particle testing; (5) Eddy current testing; (6) Radiography; (7) Ultrasonic testing; (8) Acoustic emission testing; (9) Thermography; (10) In situ metallographic examination; (11) Leak testing; (12) Comparison and selection of NDT methods; (13) Probability of detection concepts in NDT; (14) Statistical methods for quality control; and (15) Codes, Standards, Specification and Procedures.
39 citations
TL;DR: The preliminary tests reported confirm the suitability of the proposed probe for detecting cracks and correctly identifying their direction and depths.
Abstract: A low-cost probe for nondestructive testing of conductive materials was set up and tested. It is based on the measurement of the magnetic field produced by eddy currents (ECs) and perturbed by the presence of cracks. The magnetic sensor used, characterized by the authors in a previous work, gives an output that, suitably processed, allow both the amplitude and phase of the magnetic field to be measured. The preliminary tests reported confirm the suitability of the proposed probe for detecting cracks and correctly identifying their direction and depths.
34 citations
TL;DR: In this article, the electromagnetic nondestructive testing (NDT) of present interest for research and industrial applications in Japan is described, including ac and pulsed eddy-current testing, magnetic flux leakage testing, passive magnetic fluid leakage for characterization of material degradation, and various inversion techniques are presented.
Abstract: In this paper, the electromagnetic nondestructive testing (NDT) of present interest for research and industrial applications in Japan is described. Besides ac and pulsed eddy-current testing, magnetic flux leakage testing, passive magnetic flux leakage for characterization of material degradation, and various inversion techniques are presented. Both simulation and experimental results are used to demonstrate validity of the electromagnetic NDT methods.
33 citations
07 Aug 2002
TL;DR: It is shown that the use of expert knowledge-based granulation improves the quality of fault reconstruction and the best known statistical methods for fault reconstruction are not perfect.
Abstract: For large aerospace structures, it is extremely important to detect faults, and nondestructive testing is the only practical way to do it. Based on measurements of ultrasonic waves, Eddy currents, magnetic resonance, etc., we reconstruct the locations of the faults. The best (most efficient) known statistical methods for fault reconstruction are not perfect. We show that the use of expert knowledge-based granulation improves the quality of fault reconstruction.
TL;DR: In this paper, a three-layer aluminum sample from EADS Airbus was measured, with a total thickness of 62 mm, resembling the projected outer wing splice of the Airbus A-380.
Abstract: Although the sensitivity of the magnetic field sensor is important for many applications in electromagnetic testing, SQUID sensors are usually employed for other reasons. For successful defect detection, properties such as high linearity, large dynamic range, and good spatial resolution are required. We present the implementation of a SQUID magnetometer in an eddy current testing system for the measurement of very thick structures of large aircrafts. A three-layer aluminium sample from EADS Airbus was measured, with a total thickness of 62 mm, resembling the projected outer wing splice of the Airbus A-380. The sample has bolted joints and second-layer cracks adjacent to the titanium bolts. The combination of field sensitivities of a few pT/√Hz and a large dynamic range of about 140 dB/√Hz at low frequencies enables us to detect defects at a depth of up to 40 mm in aluminium. For sufficient current penetration into the layered aluminium sample, remarkably low excitation frequencies in the range of 10–40 Hz are required. The small field variations caused by the defects are superimposed on the current distortions and the corresponding field changes in the vicinity of the titanium bolts. Separation of these two contributions requires additional efforts in signal processing and simulations. The measurements were complemented by 3D-FEM calculations in order to find proper excitation frequencies, thus providing an easier separation of flaw signatures from structural background signals.
TL;DR: In this article, a neural network-based inversion technique was proposed for the inversion of signals due to outer defects in pulse eddy currents, where the amplitude of the excitation increases up to 100 times of the amplitude for an AC signal.
Abstract: Pulse eddy currents are proposed as a nondestructive testing (NDT) technique to detect flaws in conductive structures with large thickness. The harmonic component of a pulse is rich, so that the pick-up signal containing the amount of information corresponds to a multifrequency analysis. Due to the short time length of the pulse, the amplitude of the excitation increases up to 100 times of the amplitude for an AC signal. Both direct simulation of pulse eddy-currents phenomena using an A-/spl phi/ FEM-BEM code and neural network-based inversion techniques are performed. Numerical results for the inversion of signals due to outer defects are shown.
TL;DR: In this paper, a numerical method is presented for the calculation of the time-dependent response of the interaction of a stratified plate specimen of linear conductor containing a planar flaw and an eddy-current induction coil fed by a current pulse.
Abstract: A numerical method is presented for the calculation of the time-dependent response of the interaction of a stratified plate specimen of linear conductor containing a planar flaw and an eddy-current induction coil fed by a current pulse. The flaw might be located on any sides of the layers of the plate specimen. The calculations are done with the help of Fourier-transform (FT). The time-harmonic responses of the system are calculated at properly chosen frequencies, and the obtained results are weighted by the FT of the excitation to provide the FT of the response. The results of the presented method can be used for various pulsed eddy-current testing (ECT) applications.
TL;DR: In this article, the pulsed eddy current was used for detecting and quantifying fatigue cracks under installed fasteners in an aircraft NDE system, and the potential of this technique was evaluated.
Abstract: Improving the detectability of fatigue cracks under installed fasteners is one of the many goals of the aging aircraft nondestructive evaluation (NDE) community. The pulsed eddy current offers new capabilities to address this requirement. The aim of the paper is to evaluate the potential of this technique for detecting and quantifying notches under installed fasteners.
19 Nov 2002
TL;DR: In this article, an easy way to calibrate and adjust the output response of a multi-sensor probe for non-destructive testing on conductive material is proposed in order to perform the calibration, a simple coil is used, considered as a reference magnetic field generator thanks to a preliminary characterization carried out by using simulation software.
Abstract: In this paper an easy way to calibrate and adjust the output response of a multi-sensor probe for non-destructive testing on conductive material is proposed in order to perform the calibration, a simple coil is used, considered as a reference magnetic field generator thanking to a preliminary characterization carried out by using a simulation software. An FFT based algorithm was then used for probe adjustment. The calibration and adjustment apparatus can be easily integrated in the realized multi-sensor probe, so realizing a self-calibrating NDT instrument. The realized probe has then been tested on specimen with known cracks and the experimental results have been compared with the theoretical ones showing a very good agreement.
TL;DR: In this paper, the second-order vector potential formulation was used to solve the eddy current problem of a coil inside a conductive tube and in an offset position to it.
Abstract: By utilizing the second-order vector potential formulation we solve the eddy current problem of a coil inside a conductive tube and in an offset position to it. The study focuses on the derivation of a closed-form expression for the impedance change of the coil, which is used to calculate the signal produced by wobble in eddy current testing of tubes with bobbin coils.
TL;DR: In this paper, the magnetic field at the mouth of a crack in ferromagnetic steel is determined by means of a two-dimensional, linear model, and the solution is found by employing an analytical method in which one complex variable is transformed into another by using a mapping function.
Abstract: In this paper, the magnetic field at the mouth of a crack in ferromagnetic steel is determined by means of a two-dimensional, linear model. The solution is found by employing an analytical method in which one complex variable is transformed into another by means of a mapping function. An approximate boundary condition, based on the fact that the steel permeability is much larger than that of free space, is used. In this way, three representations of a crack are treated: narrow and open cracks and a semi-elliptical indentation. The mapping function transforms these shapes into a half-plane geometry for which the solution is easily obtained. The advantage of this analytical approach is that the results are readily accessible without the need for a large numerical code. Example calculations are compared with each other and with calculations based on a former theory. This work has application in electromagnetic non-destructive evaluations: eddy-current testing, flux leakage measurements and, most directly, magnetic particle inspection.
TL;DR: In this paper, a multi-coil eddy current (EC) probe is presented for high speed inspection and circumferential localization of defects in the tube wall of a steam generator.
Abstract: Steam generator (SG) tubing of pressurized water reactor in nuclear plants must be rapidly and accurately checked in order to detect defects in their early stages. In this paper, the authors present a multi-coil eddy current (EC) probe allowing both high speed inspection and circumferential localization of defects in the tube wall. A method of multi-coil EC signal processing, based on a continuous wavelet transform combined with a maximum likelihood diagnosis, is elaborated in order to enhance the detection performances and to provide automatic localization of defects. The inspection of SG tube samples shows good localization performances for defects as small as 10% deep, 15 mm long and 100 μm wide outer diameter notches, of both circumferential and axial orientations.
TL;DR: It is shown that the calculations carried out with the use of versions 4.1 of the software distributed freely via the Internet makes it possible to establish the basic relations of the problems solved and to increase significantly the accuracy and the reproducibility of the results.
Abstract: Examples of calculations of typical nondestructive testing problems with the use of the ELCUT 4.1 software designed for simulating the physical fields are given. A method which permits, using this software, to increase significantly the accuracy and the reproducibility of the results is proposed. The calculation results obtained using versions 4.1 and 4.2 of the ELCUT software are compared. It is shown that the calculations carried out with the use of versions 4.1 of the software distributed freely via the Internet makes it possible to establish the basic relations of the problems solved.
TL;DR: In this article, a new method for compensating EC signals for variations in lift-off is described, where the signals are transformed to obtain a zero liftoff equivalent signal that can be subsequently used for defect characterization.
Abstract: Eddy current (EC) testing methods are widely used in a variety of applications including the inspection of steam generator tubes in nuclear power plants, aircraft parts and airframes. A key factor that affects the EC signal is lift-off. In practice, it is difficult to keep track of the actual value of the lift-off, which is essential for accurate interpretation of the signal. Hence it is necessary to have a scheme to render the EC signal invariant to the effects of lift-off. This paper describes a new method for compensating EC signals for variations in lift-off. The signals are transformed to obtain a zero lift-off equivalent signal that can be subsequently used for defect characterization.
TL;DR: In this article, the case-hardening process modifies the near-surface permeability and conductivity of steel, as can be observed through changes in eddy current probe signals measured over a range of frequency.
Abstract: The case-hardening process modifies the near-surface permeability and conductivity of steel, as can be observed through changes in eddy current probe signals measured over a range of frequency. In this work, experiments have been performed using normal absolute probe coils on flat steel specimens and coils encircling case-hardened steel rods. By fitting model results to the experimental data, estimates of electrical material properties are found. The approach also allows an assessment of the sensitivity of the measurements to the case depth.
TL;DR: In this paper, a drive pulse and the response is analyzed in terms of Fourier transform (FT) to understand the scope of material penetration with PEC and the advantages and limitations of the technique are discussed.
Abstract: Capabilities of the Pulsed Eddy Current (PEC) method to perform in-depth scanning have been successfully demonstrated for hidden corrosion detection. In the present work, a drive pulse and the response is analyzed in terms of Fourier Transform to understand the scope of material penetration with PEC. Variations of the drive pulse shape can be an effective technique to control the depth of penetration of conductive materials. An observation time interval and a sampling rate are the components that can be used for “in-depth slicing” of conductive media. Two-dimensional scanning of multi-layered structures such as aircraft skin structures with a PEC probe provides detection of subsurface defects. Experiments have been performed on aluminum panels with flat bottom holes. An image processing routine is applied to reconstruct geometry of the component from a series of eddy current images obtained with a two-dimensional scanner. A problem of accurate reconstruction of the internal geometry of the component under test is considered. The advantages and limitations of the technique are discussed.
10 Dec 2002
TL;DR: In this paper, the ideal crack model is applied to solve the thin-opening crack problems in a conductive plate and in a tube and the Benchmark models of ECT for steam generator are calculated.
Abstract: Summary form only given. A thin-opening crack in conductive materials is very common in eddy current testing (ECT). The eddy current field problem in this case is difficult to solve using finite element methods (FEM) because fine meshes are required due to the thin width of the crack. J.R. Bowler presented the ideal crack model which assumes the thickness of the crack to be 0 and the crack to be impenetrable to eddy current. Such a flaw can be represented in terms of an equivalent current dipole layer located on its surface The dipole orientation is normal to the surface and its density can be found by solving an electric field integral equation (EFIE). Similar work has been done by J. Pavo and K. Miya. The main benefit of this approach, apart from its intuitive appeal, is that it reduces a 3D vector field problem to one of finding a single component source distribution on a surface. In this paper, the ideal crack model is applied to solve the thin flaw problems in a conductive plate and in a tube. The Benchmark models of ECT for steam generator are calculated.
TL;DR: In this paper, a 3D edge-based hexahedral finite element method was used to detect cracks on the surface of steel and the possibility of distinguishing two cracks was examined by calculating the detailed distribution of leakage flux around cracks.
Abstract: The alternating magnetic flux leakage testing has been applied in the nondestructive inspection process for detecting cracks on the surface of steel. This paper describes numerical analysis using three-dimensional (3-D) edge-based hexahedral finite element method for this testing. The necessity of nonlinear analysis is clarified in comparison with the linear analysis (j/spl omega/ method). The characteristic of leakage flux is confirmed by verification experiment. The possibility of distinguishing two cracks is examined by calculating the detailed distribution of leakage flux around cracks.
Abstract: The nondestructive evaluation (NDE) of high-temperature coatings is one of the important factors in achieving a high level of structural integrity in advanced gas turbines. In this paper, we demonstrate that sophisticated eddy-current techniques can be utilized to measure the thickness and remaining-life of high-temperature coatings. We discuss the difficult in-service case, in which the time-temperature exposure of the combustion turbine blade has created a four-layered system, in addition to the base metal.
01 Jan 2002
TL;DR: The present method employs the superposition of crack signals and a nonlinear scaling technique of a signal profile on the crack length that are verified by numerical simulation and satisfactorily predicted.
Abstract: This paper proposes a novel method for identifying the number and positions of cracks and reconstructing crack shapes. It assumes that two-dimensional scanned eddy-current testing (ECT) signals obtained from a steam generator tube are a picture image, then a template matching method with the help of genetic algorithms predicts the number and positions of cracks. The present method employs the superposition of crack signals and a nonlinear scaling technique of a signal profile on the crack length that are verified by numerical simulation. The number and positions of the cracks are satisfactorily predicted. The crack-shape reconstructions from the predicted positions with the help of inverse analysis are achieved with a satisfactory degree of accuracy.
TL;DR: In this article, an efficient numerical method to simulate eddy-current testing (ECT) of ferromagnetic steel parts is presented based on the nonlinear integral equation for quasi-stationary electromagnetic field with gauge condition based on tree/cotree decomposition.
Abstract: The paper presents an efficient numerical method to simulate eddy-current testing (ECT) of ferromagnetic steel parts. The method is based on the nonlinear integral equation for quasi-stationary electromagnetic field with gauge condition based on tree/cotree decomposition. The eddy-current density in the conductive domain and the magnetization in the ferromagnetic domain are discretized with edge elements and vectorial volume elements, respectively. A simple, but very effective magnetization model of steel in a low field is also presented. The algorithm convergence for solving the forward ECT nonlinear problem with time-periodic boundary conditions is proved.
08 Apr 2002
TL;DR: In this article, the shape of interfaces separating different phases for conductive materials made of two different conducting phases is retrieved by inversion of the measured data, and the key feature of this algorithm is that its computational cost increases linearly with the number of unknown parameters.
Abstract: Eddy current testing (ECT) is a technique used to reconstruct the unknown resistivity of conductive materials in a non-destructive way. In this technique a time-varying current flowing in an exciting coil placed near to the specimen induces eddy currents in the specimen under testing. The induced eddy currents, depending on the spatial values of the resistivity and magnetic permeability, affect the signal detected by the surrounding pick-up coils or magnetic sensors. Information concerning the spatial distribution of the resistivity is then retrieved by inversion of the measured data. In the present paper we tackle the non-linear inverse problem of retrieving the shape of interfaces separating different phases for a conductive materials made of two different conducting phases. Hence we assume that the resistivity at a given spatial coordinate assumes either the value /spl eta//sub i/ or /spl eta//sub b/. The measurement system consists of a set of coils and the measurements are the mutual impedances between coils. The main contribution of this paper is an extension to ECT measurements of a new inversion algorithm, initially proposed for electrical resistance tomography (ERT) by Rubinacci et al. The key feature of this algorithm is that its computational cost increases linearly with the number of unknown parameters.