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Recent advances in probe design for eddy current testing of heat exchangers
At present it is possible to identify automatically about 60% of the defects which are detected. By identification is meant distinguishing between microcavities and fissures. Among the 40% of poorly identified defects are fissures identified as microcavities. Considering the harmfulness of fissures, these are the misidentifications which should be eliminated. Overall, however. the results are encouraging, taking into account the uncertainties of the data. Nevertheless, it should be emphasized that if identification of defects is sometimes difficult, their localization poses no problem. If the theoretical basis of these calculations is correct, under certain conditions of control of the probe it seems possible to envisage an algorithm for classifying defects or to analyze the defects by image-processing techniques, Initial trials with the Grinnel image-processing system permit localization of defects directly from raw data. 42481
Prikhodko, V.N.; Kirillova, L.G.
Verification of the model of interaction of an eddy-current transducer with components damaged by intercrystalline corrosion Soviet Journal of Nondestructive Testing, Vol. 25, No. 1, pp. 34-37 (Sep. 1989) Experiments were carried out to examine the interaction of an eddy current attached transducer with the component damaged by intercrystalline corrosion. The experimental and theoretical results of examination are analyzed and compared.
eddy-current probe system and a localized flaw in a test piece. The model is expressed in terms of the electromagnetic fields generated by the probe in the absence of the flaw, which are evaluated on an imaging surface near or on the surface of the test piece. Assuming that the quasistatic fields scattered by the flaw are proportional to immittance coefficients that are independent of the probe position, explicit expressions for the point-spread functions of the probe are derived. Knowledge of these functions permits one to optimize probe design and identify appropriate image-processing techniques. In contrast with optical image processing, it is shown that more than one point-spread function may be required to characterize a flaw image produced by an eddy-current probe. 42281
Journal of Nondestructive Evaluation, Vol. 7, Nos 1-2, pp. 35-41 (Jun. 1988) Experimental results are presented for the change in coil impedance AZ when a circular air-cored coil carrying an alternating current of fixed frequency is scanned across a rectangular slot in an aluminium alloy plate. It is proposed that these measurements be used as a benchmark test to verify theoretical calculations of probe response in eddy-current NDE. 42279
42480
Sullivan, S.; Atherton, D.L.
The effect of an exlernal tube on the remote field eddy current effect British Journal of Nondestructive Testing, Vol. 31, No. 10, pp. 547550 (Oct. 1989) In a single tube a remote field eddy current detector gives equivalent signal responses to interior (ID) wall surface material loss as it does to equivalent exterior wall surface material loss. Results are presented in this report which show that a remote field eddy current probe can be especially sensitive to external metal objects such as an external coaxial tube or casing. It is also shown that a remote field eddy current probe does not necessarily give equivalent signals for equivalent ID and OD wall surface material loss when a particular tube is inside an external coaxial metallic tube. 42289
Hashimoto, M.; Miya, K.
Surface flaws detection of graphite materials using eddy current testing (In Japanese: English abstract) Journal of the Japanese Society of Nondestructive Inspection, Vol. 38, No. 5, pp. 420-425 (May 1989) In this paper we developed a coil for ECT (eddy current testing) for graphite material and showed its applicability to non-destructive inspection of the material. Though ECT has been successfully applied to metal, it has never been applied to the graphite material because of low electrical conductivity. In order to apply it to the material it is necessary to newly design and optimize a detecting probe and a measuring method. Characteristic features of the coil probe developed here were examined experimentally in terms of (1) lift-off effect, (2) sensitivity depending on relative location, (3) frequency dependency, and (4) coil geometry. We also conducted numerical analysis using axisymmetric and 3D eddy current analysis program to confirm experimental results. An example of detection of a corner crack will be given. 42287
Udpa, L.; Udpa, S.S.
Solution of inverse problems in eddy-current nondestructive evaluation (NDE) Journal of Nondestructive Evaluation, Vol. 7, Nos 1-2, pp. 111-120 (Jun. 1988) Eddy-current methods of nondestructive testing find widespread application in industry. The growth has been fueled, in part at least, by an increasing ability to extract information from the signal generated by the probe. This paper presents a brief overview of some of the techniques proposed for characterizing defects. Emphasis has been placed on two of the techniques developed by the authors, namely, the Fourier descriptor method and the defect reconstruction scheme using the finite-element model. 42285
Auld, B.A.," Jefferies, S.R.; Moulder, J.C.
Eddy-current signal analysis and inversion for semielliptical surface cracks Journal of Nondestructive Evaluation, Vol. 7, Nos 1-2, pp. 79-94 (Jun. 1988) A scalar potential formulation of the AZ formula for the change in impedance of an eddy-current probe caused by a surface-breaking flaw is developed. The resulting formula is evaluated using a finite- difference method, which permits calculation of AZ for semielliptical flaws. The numerical results are checked by comparing calculations for rectangular-shaped flaws to previous calculations using an analytical solution for this geometry. Theoretical results are then verified by comparison with measurements on semielliptical fatigue cracks and EDM notches in aluminum alloy specimens using air- core eddy-current probes. An inversion method that compares features of the flaw profile, obtained by scanning the eddy-current probe along the length of the flaw, to a theoretical inversion chart (McFetridge chart) is demonstrated using the experimental data. 42284
Bahr, A.J.; Auld, B.A.
An electromagnetic model, for eddy-current imaging Journal of Nondestructive Evaluation, Vol. 7, Nos 1-2, pp. 71-77 (Jun. 1988) In this paper, a model is vresented for the interaction between an
NDT International December 1990
Burke, S.K.
A benchmark problem for computation of AZ in eddy-current nondestructive evaluation (NDE)
Beissner, R.E.
Approximate model of eddy-current probe impedance for surfacebreaking flaws Journal of Nondestructive Evaluation, Vol. 7, Nos 1-2, pp. 25-34 (Jun. 1988) A theoretical model is derived for the prediction of eddy-current probe impedance changes caused by three-dimensional, surface-breaking flaws. Magnetic scalar potential theory and the surface impedance approximation are used to calculate fields on the flaw surface for arbitrary probe position and flaw geometry. Impedance changes are determined by a first-order perturbation calculation, with skin depth being the perturbation parameter. The end result is a relatively simple, three-dimensional model for simulating an eddy-current inspection. Numerical results for rectangular slots include maps of the impedance signals obtained in raster scan patterns and studies of skin-depth effects as a function of probe size, lifi-off, and flaw dimensions. 42275
Cecco, V.S.; Sharp, F.L.
Recent advances in probe design for eddy current testing of heat exchangers N D T International, Vol. 22, No. 4, pp. 217-221 (Aug. 1989) Basic eddy current principles and standard inspection procedures relating to heat exchanger tubing are briefly summarized. Various revolutionary probes recently introduced by Chalk River Nuclear Laboratories of Atomic Energy of Canada Limited are described. Included are: probes for inspecting ferromagnetic tubing, probes for detecting circumferential cracks and probes for detecting in regions, such as the tubesheet expansion zone, where conventional probes are not effective. 42271
Placko, D.; Clergeot, H.; Santander, E.
Physical modeling of an eddy current sensor designed for real time distance and thickness measurement in galvanization industry I E E E Transactions on Magnetics, Vol 25, No. 4, pp. 2861-2863 (Jul. 1989) An analytical model of an eddy current sensor designed for non-contact thickness and distance measurement is being presented. The theoretical approach for this specific class of applications finds its originality in some suggestive hypothesis, which allow a great simplification of the initial 3D problem. The analysis, made in the particular case of an iron sheet coated with a conductive material, gives an accurate interpretation of the detected signals, useful for an optimisation of the sensor design. Experimental and theoretical data are successfully compared through some industrial tests on a galvanisation line, demonstrating the prominent interest of this system in non-destructive continuous evaluation. 42270
Burais, N.; Nicolas, A.
Electromagnetic field analysis in remote field eddy current testing systems I E E E Transactions on Magnetics, Vol 25, No. 4, pp. 3010-3012 (Jul. 1989) The eddy current remote field inspection is now a widely used technique. In order to get a better knowledge of the phenomenom and to improve the performances of the method, the use of a numerical field calculation provides a large help. This paper presents the models that have been developed in order to simulate the behaviour of a probe in a remote field operation. The particularity of this model and of the related package FISSURE is to be oriented towards the NDT and NDE modelisation. So specific elements for thin cracks (crack element) and a large parametric approach and many automatic calculations appear in this package. 42269
EPR1
Preliminary assessment of an inflatable inspection probe Electric Power Research Industries, Palo Alto, California (United States), EPRI NP-5286, 64 pp. (Jul. 1987) Fitting an eddy-current test probe to steam generator tubing with an inflatable bladder could increase coverage and improve inspection sensitivity. This work resulted in the development of six highly detailed designs for an inflatable eddy-current probe. The two preferred designs were (1) an internal
361
Prikhodko, V.N.; Kirillova, L.G.
Verification of the model of interaction of an eddy-current transducer with components damaged by intercrystalline corrosion Soviet Journal of Nondestructive Testing, Vol. 25, No. 1, pp. 34-37 (Sep. 1989) Experiments were carried out to examine the interaction of an eddy current attached transducer with the component damaged by intercrystalline corrosion. The experimental and theoretical results of examination are analyzed and compared.
eddy-current probe system and a localized flaw in a test piece. The model is expressed in terms of the electromagnetic fields generated by the probe in the absence of the flaw, which are evaluated on an imaging surface near or on the surface of the test piece. Assuming that the quasistatic fields scattered by the flaw are proportional to immittance coefficients that are independent of the probe position, explicit expressions for the point-spread functions of the probe are derived. Knowledge of these functions permits one to optimize probe design and identify appropriate image-processing techniques. In contrast with optical image processing, it is shown that more than one point-spread function may be required to characterize a flaw image produced by an eddy-current probe. 42281
Journal of Nondestructive Evaluation, Vol. 7, Nos 1-2, pp. 35-41 (Jun. 1988) Experimental results are presented for the change in coil impedance AZ when a circular air-cored coil carrying an alternating current of fixed frequency is scanned across a rectangular slot in an aluminium alloy plate. It is proposed that these measurements be used as a benchmark test to verify theoretical calculations of probe response in eddy-current NDE. 42279
42480
Sullivan, S.; Atherton, D.L.
The effect of an exlernal tube on the remote field eddy current effect British Journal of Nondestructive Testing, Vol. 31, No. 10, pp. 547550 (Oct. 1989) In a single tube a remote field eddy current detector gives equivalent signal responses to interior (ID) wall surface material loss as it does to equivalent exterior wall surface material loss. Results are presented in this report which show that a remote field eddy current probe can be especially sensitive to external metal objects such as an external coaxial tube or casing. It is also shown that a remote field eddy current probe does not necessarily give equivalent signals for equivalent ID and OD wall surface material loss when a particular tube is inside an external coaxial metallic tube. 42289
Hashimoto, M.; Miya, K.
Surface flaws detection of graphite materials using eddy current testing (In Japanese: English abstract) Journal of the Japanese Society of Nondestructive Inspection, Vol. 38, No. 5, pp. 420-425 (May 1989) In this paper we developed a coil for ECT (eddy current testing) for graphite material and showed its applicability to non-destructive inspection of the material. Though ECT has been successfully applied to metal, it has never been applied to the graphite material because of low electrical conductivity. In order to apply it to the material it is necessary to newly design and optimize a detecting probe and a measuring method. Characteristic features of the coil probe developed here were examined experimentally in terms of (1) lift-off effect, (2) sensitivity depending on relative location, (3) frequency dependency, and (4) coil geometry. We also conducted numerical analysis using axisymmetric and 3D eddy current analysis program to confirm experimental results. An example of detection of a corner crack will be given. 42287
Udpa, L.; Udpa, S.S.
Solution of inverse problems in eddy-current nondestructive evaluation (NDE) Journal of Nondestructive Evaluation, Vol. 7, Nos 1-2, pp. 111-120 (Jun. 1988) Eddy-current methods of nondestructive testing find widespread application in industry. The growth has been fueled, in part at least, by an increasing ability to extract information from the signal generated by the probe. This paper presents a brief overview of some of the techniques proposed for characterizing defects. Emphasis has been placed on two of the techniques developed by the authors, namely, the Fourier descriptor method and the defect reconstruction scheme using the finite-element model. 42285
Auld, B.A.," Jefferies, S.R.; Moulder, J.C.
Eddy-current signal analysis and inversion for semielliptical surface cracks Journal of Nondestructive Evaluation, Vol. 7, Nos 1-2, pp. 79-94 (Jun. 1988) A scalar potential formulation of the AZ formula for the change in impedance of an eddy-current probe caused by a surface-breaking flaw is developed. The resulting formula is evaluated using a finite- difference method, which permits calculation of AZ for semielliptical flaws. The numerical results are checked by comparing calculations for rectangular-shaped flaws to previous calculations using an analytical solution for this geometry. Theoretical results are then verified by comparison with measurements on semielliptical fatigue cracks and EDM notches in aluminum alloy specimens using air- core eddy-current probes. An inversion method that compares features of the flaw profile, obtained by scanning the eddy-current probe along the length of the flaw, to a theoretical inversion chart (McFetridge chart) is demonstrated using the experimental data. 42284
Bahr, A.J.; Auld, B.A.
An electromagnetic model, for eddy-current imaging Journal of Nondestructive Evaluation, Vol. 7, Nos 1-2, pp. 71-77 (Jun. 1988) In this paper, a model is vresented for the interaction between an
NDT International December 1990
Burke, S.K.
A benchmark problem for computation of AZ in eddy-current nondestructive evaluation (NDE)
Beissner, R.E.
Approximate model of eddy-current probe impedance for surfacebreaking flaws Journal of Nondestructive Evaluation, Vol. 7, Nos 1-2, pp. 25-34 (Jun. 1988) A theoretical model is derived for the prediction of eddy-current probe impedance changes caused by three-dimensional, surface-breaking flaws. Magnetic scalar potential theory and the surface impedance approximation are used to calculate fields on the flaw surface for arbitrary probe position and flaw geometry. Impedance changes are determined by a first-order perturbation calculation, with skin depth being the perturbation parameter. The end result is a relatively simple, three-dimensional model for simulating an eddy-current inspection. Numerical results for rectangular slots include maps of the impedance signals obtained in raster scan patterns and studies of skin-depth effects as a function of probe size, lifi-off, and flaw dimensions. 42275
Cecco, V.S.; Sharp, F.L.
Recent advances in probe design for eddy current testing of heat exchangers N D T International, Vol. 22, No. 4, pp. 217-221 (Aug. 1989) Basic eddy current principles and standard inspection procedures relating to heat exchanger tubing are briefly summarized. Various revolutionary probes recently introduced by Chalk River Nuclear Laboratories of Atomic Energy of Canada Limited are described. Included are: probes for inspecting ferromagnetic tubing, probes for detecting circumferential cracks and probes for detecting in regions, such as the tubesheet expansion zone, where conventional probes are not effective. 42271
Placko, D.; Clergeot, H.; Santander, E.
Physical modeling of an eddy current sensor designed for real time distance and thickness measurement in galvanization industry I E E E Transactions on Magnetics, Vol 25, No. 4, pp. 2861-2863 (Jul. 1989) An analytical model of an eddy current sensor designed for non-contact thickness and distance measurement is being presented. The theoretical approach for this specific class of applications finds its originality in some suggestive hypothesis, which allow a great simplification of the initial 3D problem. The analysis, made in the particular case of an iron sheet coated with a conductive material, gives an accurate interpretation of the detected signals, useful for an optimisation of the sensor design. Experimental and theoretical data are successfully compared through some industrial tests on a galvanisation line, demonstrating the prominent interest of this system in non-destructive continuous evaluation. 42270
Burais, N.; Nicolas, A.
Electromagnetic field analysis in remote field eddy current testing systems I E E E Transactions on Magnetics, Vol 25, No. 4, pp. 3010-3012 (Jul. 1989) The eddy current remote field inspection is now a widely used technique. In order to get a better knowledge of the phenomenom and to improve the performances of the method, the use of a numerical field calculation provides a large help. This paper presents the models that have been developed in order to simulate the behaviour of a probe in a remote field operation. The particularity of this model and of the related package FISSURE is to be oriented towards the NDT and NDE modelisation. So specific elements for thin cracks (crack element) and a large parametric approach and many automatic calculations appear in this package. 42269
EPR1
Preliminary assessment of an inflatable inspection probe Electric Power Research Industries, Palo Alto, California (United States), EPRI NP-5286, 64 pp. (Jul. 1987) Fitting an eddy-current test probe to steam generator tubing with an inflatable bladder could increase coverage and improve inspection sensitivity. This work resulted in the development of six highly detailed designs for an inflatable eddy-current probe. The two preferred designs were (1) an internal
361