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Sizing radial cracks in bores holes by eddy current
N DT Abstracts 40143
Nakqawa,
N.; Kogan,
V.G.; Bozzoln,
noise for remote field scans detecting relatively small external tube wall surface defects. Sensitivity is enhanced by balancing the probe against an external reference signal.
G.
Effect of crack closure on eddy current signals Review of Progress in Quantitative Nondestructive Evaluation, Williamsburg, Virginia (United States), 22-26 Jun. 1987. Vol. 7A, pp. 173-179. Edited by D.D. Thompson and D.E. Chimenti, Plenum Press, 1988. The subject of this report is a theoretical study of eddy current signals
3766 I
Moulder,
J.C.; Nakagawa,
N.; Shull, P.J.
Process in uniform field eddy current methods Review of Progress in Quantitative Nondestructive Evaluation, Williamsburg, Virginia (United States), 22-26 Jun. 1987. Vol. 7A, pp. 147- 155.Edited by D.D. Thompson and D.E. Chimenti, Plenum
37619
Cecco, VS.; Sharp, F.L.
Canadian Society of Nondestructive Testing Journal, Vol. 9, No. 3, pp. 32-34, 36 (May-Jun. 1988) Progress in the scope 01’ eddy current testing is thought to lie in improvements to probe design to improve signal-to-noise ratios. A number of probes developed at the Chalk River Laboratories of Atomic Energy of Canada are described in this. paper. Improvements to detecting shallow defects with surface probes can be made by minimizing lift off noise and discriminating between lift-off noise and the signal. A surface probe which maximizes the defect signal relative to extraneous signals is used for detecting deep subsurface defects. Two probes for heat exchangers have been developed, one with support/expansion compensation and one for carbon steel tubes. All the probes described can be used with standard, commercially available instruments.
36883
J.; Seretti, A.; Samson, R.
the calibration are discussed.
36875
Dissertation Abstracts International,
Vol. 47, No. 8, p. 3463 (Feb.
1987) The objective of this research is to: (I) Effectively increase the penetrationdepth by improving the signal to noise ratio of the detected eddy current signal. (2) Use this signal in identifying voids, cracks, or other anomalies to the tested material. (3) Improve the maximum resolution to the system and as a result scale the signal’s signature so that the defect size, depth and georretric nature can be identified.
36607 Cross, M.T.: Watson, P.C. Digital data acquisition and signal processing of eddy-current data from nuclear fuel rod3 United Kingdom Atomic Energy Authority, Windscale Nuclear Power Development Laboratories, ND-R-1436(W), 2Opp (Dec. 1986)
S.; Daly, M.
A remote-field eddy current tool for inspecting nuclear reactor pressure tubes
Software-based, digital signal processing techniques for the enhancement of ec’dy-current signals buried in background noise are presented. A microcomputer is used to provide cross-correlation and digital mixing of dual frequency eddy-current test data in order to enhance the signals obtained from small defects in reactor fuel cladding. Tests have shown the system to be effective, particularly in the enhancement of signals obtained from pencil-probe transducers thus improving the reliability of defect detcrmin3tions on fuel rods.
British Journal of Nondestructive Testing, Vol. 30, No. 1, pp. 22-27 (Jan.
Cavcey, K.H.
The characteristics of a time variant magnetic field near a defect in a metal due to induced pulsed eddy currents
Fatigue strain on metallic structure assembled by rivets or fasteners can lead to the development of some fatigue cracks in the bores holes. When rivets or fasteners can be removed cracks detection and orientation is very easy using eddy current methods. Avions Marcel Dassault-Breguet Aviation (AMD-BA) did a preliminary study with commercially available equipment. A dedicated piece of equipment for sizing fatigue h% been developed. This equipment scans the bore hole (automatically) and inspects it. Once the crack has been detected, the orientation, localisation, sizing and profiling are done with industrial accuracy eddy current signal and crack identification correlation has been made possible by the use of eddy current mechanic control (4 axis), advanced digital equipment, absolute and differential measurements with the same probe and customized software. For the presentation, many AMD-BA results will be shown especially on laboratory fatigue crack samples and on aircraft inspection.
D.L.; Sullivan,
Wittig, G.
Materialprufung, Vol.29, No.5, pp. 121-124 (May 1987) Because oi the shape indications of the rivets it is difficult to detect cracks in a hidden position within an aluminium structure. The crack indications were to separate from the indications of the rivets by use of a special coil system, which was manufactured on the basis of a toroidal core. On examples the signal paths in the complex voltage plan or as curves dependent on the local position measured during a local scan were demonstrated. Details about the minimum detectability and questions about
Proceedings of the 16th Symposium on Nondestructive Evaluation, San Antonio, Texas (United States), 21-23 Apr. 1987. pp. 194-202. Nondestructive Testing Information Analysis Center, Texas, USA.
Atherton,
T.E.
Investigations about the crack detection on aluminium structures joint by rivets by the eddy current method (In German)
Sizing radial cracks in bores holes by eddy current
37922
J.C.; Capohianco,
In a new approach to eddy current detection and sizing of surfacebreaking flaws, a conventional reflection probe has been coupled to a superconducting quantum interference device (SQUID) to produce an eddy current probe with incrzased sensitivity and signal to noise ratio. The reflection probe consists of an air-core excitation coil surrounding two counterwound ferrite-ccre pickup coils connected in series. A roomtemperature probe is inductively coupled to a SQUID, which operates in a-liquid helium bath. The new probe is used to obtain flaw signals from a number of electrical-discharge machined slots in aluminum alloy 6061. Results indicate that by scanning the probe along the length of the flaw, the length can be determined from the extent of the flaw signal. The peak amplitude of the flaw signal is found to be proportional to the cross-sectional area of the flaw. Empirical calibration curves relating these quantities are used to invart successfully the experimental data obtained for the EDM slots.
Probes to overcome eddy current limitations
Bernardi,
Moulder,
Journal of Research of the National Bureau of Standards. Vol. 92, No. 1, pp. 27-33 (Jan./Feb. 1987)
In the uniform field eddy current (UFEC) technique, a specially designed probe is used to interrogate surface-breaking flaws with a spatially uniform, time-varying magnetic field. Because of the skin effect, the surface current decays exponentially with penetration into the metal with a characteristic length, the skirt depth. Interaction of the current with any cracks, voids, or other defects near the surface causes a small change in probe impedance. For the case of surface- breaking cracks and slots, at high frequencies. when the skin depth is less than the depth of the flaw. Auld’s formula for the change in probe impedance caused by the flaw is remarkably accurate. In this paper further evidence is offered that the cause of the errors was crack closure and show how a magnitude-phase plot of the flaw signal can reveal the occurrence of closure.
39648
Limited
Detection and sizing of surface flaws with a SQUID-based eddy current probe
Press, 1988.
39758
Electronics
U.S. Patent no. 4,609,870 (2 Sep. 1986) An eddy current crack detection system is comprised of an inductive probe coil forming part of an oscillatory circuit and a measuring device arranged to monitor the amplitude of the oscillating voltage across the probe coil. In order to substantially nullify the effect of lift-off on the amplitude of the voltage a variable electrical resistance in the oscillatory circuit is provided. Control means, responsive to the instantaneous magnitude of lift-off, provide a control signal for continuously varying the value of the resistance and hence the amount of damping in the oscillatory circuit so that the amplitude of the voltage does not vary substantially with lift-off.
caused by cracks occurring near metal surfaces. Particular attention is paid to the crack-closure problem: :suppose that an open flaw with a finite width w is given. The situation considered is that of the crack first becoming tightly closed and , eventually ,developing electrical contacts inside the crack region. The uniform-field-probe signals caused by these cracks are calculated. While the transition is smooth, the impedance signal shows dramatic changes in the process. 40140
Hocking
Lift off compensation of eddy current crack detection system by controlling damping resistance of oscillator
1988)
The remote-field eddy current technique for inspecting non-magnetic, zirconium - 2% niobium-allay pressure tubes, which are used in CANDU system nuclear reactors, has teen developed in laboratory tests. Techniques used to optimize the operatirlg performance of the remote field probe are described. Experimental resu’lts are presented showing excellent signal-to-
183
Nakqawa,
N.; Kogan,
V.G.; Bozzoln,
noise for remote field scans detecting relatively small external tube wall surface defects. Sensitivity is enhanced by balancing the probe against an external reference signal.
G.
Effect of crack closure on eddy current signals Review of Progress in Quantitative Nondestructive Evaluation, Williamsburg, Virginia (United States), 22-26 Jun. 1987. Vol. 7A, pp. 173-179. Edited by D.D. Thompson and D.E. Chimenti, Plenum Press, 1988. The subject of this report is a theoretical study of eddy current signals
3766 I
Moulder,
J.C.; Nakagawa,
N.; Shull, P.J.
Process in uniform field eddy current methods Review of Progress in Quantitative Nondestructive Evaluation, Williamsburg, Virginia (United States), 22-26 Jun. 1987. Vol. 7A, pp. 147- 155.Edited by D.D. Thompson and D.E. Chimenti, Plenum
37619
Cecco, VS.; Sharp, F.L.
Canadian Society of Nondestructive Testing Journal, Vol. 9, No. 3, pp. 32-34, 36 (May-Jun. 1988) Progress in the scope 01’ eddy current testing is thought to lie in improvements to probe design to improve signal-to-noise ratios. A number of probes developed at the Chalk River Laboratories of Atomic Energy of Canada are described in this. paper. Improvements to detecting shallow defects with surface probes can be made by minimizing lift off noise and discriminating between lift-off noise and the signal. A surface probe which maximizes the defect signal relative to extraneous signals is used for detecting deep subsurface defects. Two probes for heat exchangers have been developed, one with support/expansion compensation and one for carbon steel tubes. All the probes described can be used with standard, commercially available instruments.
36883
J.; Seretti, A.; Samson, R.
the calibration are discussed.
36875
Dissertation Abstracts International,
Vol. 47, No. 8, p. 3463 (Feb.
1987) The objective of this research is to: (I) Effectively increase the penetrationdepth by improving the signal to noise ratio of the detected eddy current signal. (2) Use this signal in identifying voids, cracks, or other anomalies to the tested material. (3) Improve the maximum resolution to the system and as a result scale the signal’s signature so that the defect size, depth and georretric nature can be identified.
36607 Cross, M.T.: Watson, P.C. Digital data acquisition and signal processing of eddy-current data from nuclear fuel rod3 United Kingdom Atomic Energy Authority, Windscale Nuclear Power Development Laboratories, ND-R-1436(W), 2Opp (Dec. 1986)
S.; Daly, M.
A remote-field eddy current tool for inspecting nuclear reactor pressure tubes
Software-based, digital signal processing techniques for the enhancement of ec’dy-current signals buried in background noise are presented. A microcomputer is used to provide cross-correlation and digital mixing of dual frequency eddy-current test data in order to enhance the signals obtained from small defects in reactor fuel cladding. Tests have shown the system to be effective, particularly in the enhancement of signals obtained from pencil-probe transducers thus improving the reliability of defect detcrmin3tions on fuel rods.
British Journal of Nondestructive Testing, Vol. 30, No. 1, pp. 22-27 (Jan.
Cavcey, K.H.
The characteristics of a time variant magnetic field near a defect in a metal due to induced pulsed eddy currents
Fatigue strain on metallic structure assembled by rivets or fasteners can lead to the development of some fatigue cracks in the bores holes. When rivets or fasteners can be removed cracks detection and orientation is very easy using eddy current methods. Avions Marcel Dassault-Breguet Aviation (AMD-BA) did a preliminary study with commercially available equipment. A dedicated piece of equipment for sizing fatigue h% been developed. This equipment scans the bore hole (automatically) and inspects it. Once the crack has been detected, the orientation, localisation, sizing and profiling are done with industrial accuracy eddy current signal and crack identification correlation has been made possible by the use of eddy current mechanic control (4 axis), advanced digital equipment, absolute and differential measurements with the same probe and customized software. For the presentation, many AMD-BA results will be shown especially on laboratory fatigue crack samples and on aircraft inspection.
D.L.; Sullivan,
Wittig, G.
Materialprufung, Vol.29, No.5, pp. 121-124 (May 1987) Because oi the shape indications of the rivets it is difficult to detect cracks in a hidden position within an aluminium structure. The crack indications were to separate from the indications of the rivets by use of a special coil system, which was manufactured on the basis of a toroidal core. On examples the signal paths in the complex voltage plan or as curves dependent on the local position measured during a local scan were demonstrated. Details about the minimum detectability and questions about
Proceedings of the 16th Symposium on Nondestructive Evaluation, San Antonio, Texas (United States), 21-23 Apr. 1987. pp. 194-202. Nondestructive Testing Information Analysis Center, Texas, USA.
Atherton,
T.E.
Investigations about the crack detection on aluminium structures joint by rivets by the eddy current method (In German)
Sizing radial cracks in bores holes by eddy current
37922
J.C.; Capohianco,
In a new approach to eddy current detection and sizing of surfacebreaking flaws, a conventional reflection probe has been coupled to a superconducting quantum interference device (SQUID) to produce an eddy current probe with incrzased sensitivity and signal to noise ratio. The reflection probe consists of an air-core excitation coil surrounding two counterwound ferrite-ccre pickup coils connected in series. A roomtemperature probe is inductively coupled to a SQUID, which operates in a-liquid helium bath. The new probe is used to obtain flaw signals from a number of electrical-discharge machined slots in aluminum alloy 6061. Results indicate that by scanning the probe along the length of the flaw, the length can be determined from the extent of the flaw signal. The peak amplitude of the flaw signal is found to be proportional to the cross-sectional area of the flaw. Empirical calibration curves relating these quantities are used to invart successfully the experimental data obtained for the EDM slots.
Probes to overcome eddy current limitations
Bernardi,
Moulder,
Journal of Research of the National Bureau of Standards. Vol. 92, No. 1, pp. 27-33 (Jan./Feb. 1987)
In the uniform field eddy current (UFEC) technique, a specially designed probe is used to interrogate surface-breaking flaws with a spatially uniform, time-varying magnetic field. Because of the skin effect, the surface current decays exponentially with penetration into the metal with a characteristic length, the skirt depth. Interaction of the current with any cracks, voids, or other defects near the surface causes a small change in probe impedance. For the case of surface- breaking cracks and slots, at high frequencies. when the skin depth is less than the depth of the flaw. Auld’s formula for the change in probe impedance caused by the flaw is remarkably accurate. In this paper further evidence is offered that the cause of the errors was crack closure and show how a magnitude-phase plot of the flaw signal can reveal the occurrence of closure.
39648
Limited
Detection and sizing of surface flaws with a SQUID-based eddy current probe
Press, 1988.
39758
Electronics
U.S. Patent no. 4,609,870 (2 Sep. 1986) An eddy current crack detection system is comprised of an inductive probe coil forming part of an oscillatory circuit and a measuring device arranged to monitor the amplitude of the oscillating voltage across the probe coil. In order to substantially nullify the effect of lift-off on the amplitude of the voltage a variable electrical resistance in the oscillatory circuit is provided. Control means, responsive to the instantaneous magnitude of lift-off, provide a control signal for continuously varying the value of the resistance and hence the amount of damping in the oscillatory circuit so that the amplitude of the voltage does not vary substantially with lift-off.
caused by cracks occurring near metal surfaces. Particular attention is paid to the crack-closure problem: :suppose that an open flaw with a finite width w is given. The situation considered is that of the crack first becoming tightly closed and , eventually ,developing electrical contacts inside the crack region. The uniform-field-probe signals caused by these cracks are calculated. While the transition is smooth, the impedance signal shows dramatic changes in the process. 40140
Hocking
Lift off compensation of eddy current crack detection system by controlling damping resistance of oscillator
1988)
The remote-field eddy current technique for inspecting non-magnetic, zirconium - 2% niobium-allay pressure tubes, which are used in CANDU system nuclear reactors, has teen developed in laboratory tests. Techniques used to optimize the operatirlg performance of the remote field probe are described. Experimental resu’lts are presented showing excellent signal-to-
183