- Email: [email protected]
Remote field eddy current examination for U-shape ferromagnetic heat- exchanger tubes (In Japanese: English Abstract)
N DT Abstracts reference signal to generate a flaw signal representative of flaws in the metal
eddy current testing has been employed as a primary inspection tool. Detection of pitting has not caused a major inspection problem, but the traditional phase angle-to-pit depth analysis has not been reliable. This paper presents a more reliable sizing technique based on signal amplitude.
pipe. 565 12
Rajesh, S.N.
Probability of detection models for eddy current NDE methods
54758 Rajesh, S.N.; Udpa, L.; Udpa, S.S. Estimation of eddy current probability of detection (POD) using finite element method
Ames Lab., Iowa (United States), DE94007059/GAR, 106~~. (30 Apr. 1993) This thesis presents a comprehensive POD model for eddy current NDE. Eddy current methods of nondestructive testing are used widely in industry to inspect a variety of nonferromagnetic and ferromagnetic materials. The development of a comprehensive POD model is therefore of significant importance. The model incorporates several sources of variability characterized by a multivariate Gaussian distribution and employs finite element analysis to predict the signal distribution. The method of mixtures is then used for estimating optimal threshold values. The research demonstrates the use of a finite element model within a probabilistic frame-work to the spread in the measured signal for eddy current nondestructive methods.
Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 19-24 Jul. 1992. Vol. 12B, pp.2365-2372. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1993) ISBN 0- 306-44483-6 This paper presents a comprehensive POD model for eddy current NDE. The model incorporates several sources of variabilities characterized by a multivariate Gaussian distribution and employs the finite element method to predict the signal distribution. The paper demonstrates the use of a finite element model within a probabilistic framework to predict the spread of the measured signal for eddy current nondestructive methods. Using the signal distributions for various flaw sizes the probability of detection curves for defects of varying widths have been computed. Results demonstrating the value and utility of the approach are presented. In contrast to experimental POD models, the cost of generating such curves is very low and complex defect shapes can be handled very easily. The results are also operator independent.
55778 Gerasimnv, V.G.; Malov, V.M.; Efraimov, L.Y.; Evdokimov, P.A.
Eddy-current inspection of carbon components Russian Journal of Nondestructive Testing, Vol. 29, No. 9, pp. 643-649 (May 1994) Problems of eddy-current inspection of carbon-carbon composites are considered. A method is described for approximate calculation of signals of a superposed eddy-current transducer from defects of the crack type. The results are reported from experimental studies of samples of carbon-carbon composites with and without defects. The block diagram is given along with a description of the software for a device for detecting surface cracks in products made of those composites. 54987
54757 Placko. D.; Dufour, I. Eddy current sensors for nondestructive inspection of graphite composite materials 27th Annual Meeting of the Industry Applications, Houston (United States), 4-9 Oct. 1992. Vol. 2, pp. 1676-1682. IEEE (1992) ISBN 078030634 1 A system using eddy current sensors for nondestructive evaluation of graphite composite plates is described. First, the basic physical principle of measurements with this kind of sensors is recalled. Then, an analytical model of the relationships between the properties of the object approached in the sensitive area of the sensor and the induced variation of signal is presented: in our case, the interesting properties are the distance between the sensor and the plate, and its local conductivity. In the second part, the inversion of this model is discussed in view to extract the useful data from the sensor signal. This method is then illustrated in the case of a graphite composite plate on which a mechanical constraint is applied. The inspection process consists in scanning the sensor above the surface of the sample, and computing in each point either values of distance or conductivity. Both these results presented at successive steps of structure damages show simultaneously the surface deformations and the internal defects in the sample, demonstrating the interest of our method.
Delsarte, G.; Levy, R.
Mascotte, an analytical model for eddy current signals I I th International Conference and Exhibits on NDE in the Nuclear and Pressure Vessel Industries, Albuquerque, New Mexico (United States). 30 Apr. - 2 May 1992. pp. 283-288. ASM International (1992). ISBN O-87170- 446-3 Mascot@ a physical model including simple approximations, is applied to discontinuities such as wall-losses, inclusions and complex defects on a non ferromagnetic tube examined with a bobbin coil probe. The eddy current signal is described by analytical formulations which take into account the environmental parameters: tube dimension, probe design, excitation frequency, and physical features of the defect. Moreover, the simulated signal can be combined with the actual signal from a known discontinuity such as a supportplate. 54986 c.
Coutanceau-Monteil,
N.; Billy, F.; Cahouet. J.; Chavant.
54543 Wincheski, B.; Fulton, J.P.; Nath, S.; Namkung, M.; Simpson, J. W.
A complementary approach of 2D and 3D modeling for the understanding and the design of pulsed eddy current probes 1I th International Conference and Exhibits on NDE in the Nuclear
Self-nulling eddy current probe for surface and subsurface flaw detection Materials Evaluation, Vol. 52, No. 1, pp. 22-26 (Jan. 1994)
and Pressure Vessel Industries, Albuquerque, New Mexico (United States), 30 Apr. - 2 May 1992. pp. 273-276. ASM International (1992). ISBN O-87170- 446-3 In order to improve Pulsed Eddy Current (PEC) techniques for detecting and sizing subsurface cracks in non magnetic metals, numerical modelling and experiments are performed. The impulse response of the probe is simulated with a 2D finite element code and compared with experimental data. It is shown that 2D modelling for both axisymetrical and plane representations doesn’t simulate the interaction of the PEC probe with a subsurface plane electron-discharge machined (EDM) slot. On the contrary, 3D modelling performed with the TRIFOU code confirms experimental observations such as the. directivity of the probe and the tip effect from the slot. The sensitivity of the signal to the depth and orientation of the flaw and to the location and orientation of the receiving coil (i.e., various probes) is discussed. It is thus possible to size the length of the flaw through tip detection.
An eddy current probe. that provides a null-signal in the presence of unflawed material without the need for any balancing circuitry has been developed at NASA Langley Research Center. This capability reduces set-up time, eliminates tester configuration errors, and decreases instrumentation requirements. The probe is highly sensitive to surfacebreaking fatigue cracks, and shows excellent resolution for the measurement of material thickness, including material loss due to corrosion damage. The presence of flaws in the material under test causes an increase in the extremely stable and reproducible output voltage of the probe. The design of the probe and some examples illustrating its flaw detection capabilities are presented. 54283
Combustion Engineering Inc.; (Edwards, L.J.)
Method for detecting flaws in a steam generator tube using a flexible eddy current probe having coil band switching U.S. Patent No. 5,256,966 (26 Oct. 1993) A method of detecting flaws in a tube is described. It has a probe assembly with a probe heat with two sets of coils. A bank switch allows switching between the coils. Output signals are received which are transmitted over conductors from the coils, representative of the flaws.
54983 Krzywosz, K.; Henry, G.; O’Brien, J. Eddy current pit sizing techniques for copper alloy tubing 11th International Conference and Exhibits on NDE in the Nuclear and Pressure Vessel Industries, Albuquerque, New Mexico (United States), 30 Apr. - 2 May 1992. pp. 345-352. ASM International ( 1992). ISBN O-87170- 446-3 Copper based alloy tubing utilized in power plant heat exchangers is susceptible to pitting on the inside tube surface. Localized pitting is most damaging since it reduces load-carrying capacity and increases stress concentration by creating holes in the tube wall. To assesstubing integrity,
54222
Sakamoto, T.
Remote
field
ferromagnet.ic Abstract) Journal of
174
eddy
current
heat- exchanger
for (In Japanese:
examination tubes
U-shape English
JSNDI, Vol. 42, No. 10, pp. 563-569 (Oct. 1993)
N DT Abstracts It comprises several coils inserted axially into the metal pipe including an exciting coil for receiving an alternating current and generating field eddy current signals and two receiving coils. A differential signal representing the vectorial difference between eddy current signals from the two coils is obtained. The phase of this signal is compared to a reference signal to determine the presence of flawed regions of the pipe based on the cumulative offset amplitude.
The remote field Eddy current technique (RFECT) is the unique potential method capable of inspecting U-shape ferromagnetic heatexchanger tubes. Basic experimental study on RFECT has been part of 45 mm in minimum radius. While: higher test frequency generates larger defect signal, it causes the rapid increase of magnetic noise in general which is observed in conventional eddy current testing. Based on experimental work, it is proved that both tube wall and electromagnetic characteristics determine the optimum test frequency. in which defects can be detected with high signal to noise ratio. In comparison of defect detectability in the straight tube part, inner coil eddy current method with strong magnetizing ability is superior to RFECT method in the case of thin wall thickness less than 2 mm. Therefore it is necessary for high accurate inspection to use both testing methods.
53284
U.S. Patent No. 5,184,070 (2 Feb. 1993) An eddy current test instrument with a rotary head with at least two test heads is described. The heads include eddy current test probes mounted on a circular track to scan a part. The defect signals are processed and evaluated.
54036 Hedengren, K.H.; Hurley, D.C.; Kornrumpf, W.P.; Young, J.D.; Sutton, G.H.
53282 Young, J.D.; Hedengren, K.H.; Hurley. D.C. Method and apparatus for a multi-channel multi-frequency data acquisition system for nondestructive eddy current inspection testing
An array system for fast, sensitive eddy current inspections ASNT 1993 Fall Conference and Quality Testing Show. NDT: A Partner in Engineering Innovation, Long Beach, California (United States), 8-12 Nov. 1993. pp. 51-53. ASNT (1993) A unique eddy current array system for non-destructive testing has been developed by GE. Conformable sensor arrays, multiplexing multichannel data acquisition electronics, hybrid electronic/mechanical scanning for rapid complete surface coverage, and signal/image processing for automatic flaw detection are key features of the system. The system, which is the first of its kind in the world, has been in use for production inspections of turbine disk dovetail slots at a GE manufacturing plant since September 1992. The inspection coverage rate is more than an order of magnitude faster than with the previous single probe process, while maintaining required defect sensitivity.
54027
U.S. Patent No. 5,182,513 (26 Jan. 1993) An eddy current inspection apparatus for detecting flaws in a conductive surface. is described. It consists of several eddy current probes: a means of automatically scanting the surface and multiplexing and demodulating the measurement signal. It also has a means for automated image processing of the digital components of the signals. 53027
Alabama Univ., in Huntsville, (United States), N93-12875/9/GAR, 22pp. (18 Jul. 1991) The use of eddy current techniques for characterizing flaws in graphite-based filament-wound cylindrical structures is described. A major emphasis was also placed upon incorporating artificial intelligence techniques into the signal analysis portion of the inspection process. Developing an eddy current scanning system using a commercial robot for inspecting graphite structures (and others) was a goal in the overall concept and is essential for the final implementation for the expert systems interpretation.
Bowler, J.R.; Harrison, D J.; Norton, S.J.
Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 19-24 Jul. 1992. Vol. 12A, pp. 243-249. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1993). ISBN O-306-44483-6. This paper is mainly concerned with computational issues, though we shall briefly touch on analytical questions concerning the nature of the gradients. The object of the present inversion study is a crack with zero opening yet acting as a perfect barrier to electric current. The shape of this ideal crack is described by a flaw function which expresses the position of the crack edge as the equation of a line. Once the equation of the line has been found, the length, maxima depth and the geometry of the crack profile can be deduced.
53527
Atherton, D.L.; Mackintosh, D.D.; Sullivan, S.P.; Duhois. 53024 J.M.S.; Schmidt, T.R.
Remote-field eddy current signal representation Materials
Vol. 5 1, No. 7, pp. 782-789
(Jul. 1993)
scope monitor displays customarily used for conventional exploring coil ET probes in tubes. We then present the normalized voltage plane and monitor displays that are most appropriate for RFEC probes. We discuss the similarities and differences between the preferred monitor displays.
Sakamoto, T.; Fujiwara, H.
of
53022
Stepinski, T.: Maszi, N.
Conjugate spectrum filters for eddy current signal processing
(1993) Magnetic saturation is applied to ferromagnetic tubes inspected by the encircling or inner coil because suppressing magnetic noise is important for the eddy current testing technique. Eddy current signal characteristics in magnetically saturated tubes are different from those in nonmagnetic tubes. In ferromagnetic tubes, defect signal phase angle is not useful for estimating defect depth because it does not depend on the defect depth. In this paper, numerical eddy current analysis has been done in order to explain the relationship between the defect depth and the phase angle in magnetically saturated tubes.
Materials Evaluation, Vol. 5 1, No. 7, pp. 839-844 (Jul. 1993) The paper addresses the problem of detection and classification of material defects during eddy current inspection. Digital signal processing algorithms for detection and characterization of flaws are considered and a new type of filter for classification of eddy current data is proposed. In the first part the signal processing blocks used in modem eddy current instruments are presented and analyzed in terms of information transmission. A method is then presented which employs two-dimensional conjugate spectrum filters (CSFs) that are sensitive both the the phase angle and the shape of the eddy current responses.
Cueman, M.K.; Hurley, D.C.; Tuck, P.B.
52753
Method a’nd apparatus for making spatially correlated eddy current measurements
Mackintosh, D.D.; Atherton, D.L.; Puhach, P.A.
Through-transmission equations for remote-field eddy current inspection of small-bore ferromagnetic tubes
U.S. Patent No. 5,175.498 (29 Dec. 1992)
Materials
An apparatus for measurin,g flaws in an object having both erratic and net motions is described. It has a means for sensing the motion of the object and detecting any flaws. The flaw signal is corrected to erratic motion by a triggered (A/D) converter. 53305
Evaluation,
Here we first of all summarize the impedance plane representation and
Research in Nondestructive:Evaluation, Vol. 5, No. 2, pp. 135-146
53323
Workman, G.L.
Automated eddy current analysis of materials. Final report
Inversion of eddy current probe impedance data for crack reconstruction
Numerical analysis for eddy current characteristics magnetically saturated ferromagnetic tubes
Besendorfer, H.; Stritzke, G.; Haditsch, F.
Eddy-current defect test instrument with multiple test probes and one distance probe
Evaluation,
Vol. 5 1, No. 6, pp. 744-748
(Jun. 1993)
Experimentally measured deviations from skin depth theory are described. A theoretical investigation is made of through-transmission for a cylindrical wave impinging on a conducting tube. The cylindrical throughtransmission equations agree well with RFEC data. The application 0: the new equations to RFEC defect signal analysis is discussed. A case study of an RFEC scan of a metal loss defect is described. The through-transmission equations were found to hold at the defect. However, the RFEC scan data deviated slightly from the value predicted by the through-transmission equations. The deviation was attributed to a perturbation of the field on the outside of the pipe caused by the defect, an effect no considered in a
Hosohara. Y.; Suzuki, K.; Fujiwara, S.; Kawahe, T.
Remote field eddy current flaw detector for metal pipes having a pair of receiver coils providing a differential offset amplitude signal U.S. Patent No. 5,210,492 (I I May 1993)
through- transmission analysis.
A remote field eddy current detector for detecting flaws in a metal pipe.
175
eddy current testing has been employed as a primary inspection tool. Detection of pitting has not caused a major inspection problem, but the traditional phase angle-to-pit depth analysis has not been reliable. This paper presents a more reliable sizing technique based on signal amplitude.
pipe. 565 12
Rajesh, S.N.
Probability of detection models for eddy current NDE methods
54758 Rajesh, S.N.; Udpa, L.; Udpa, S.S. Estimation of eddy current probability of detection (POD) using finite element method
Ames Lab., Iowa (United States), DE94007059/GAR, 106~~. (30 Apr. 1993) This thesis presents a comprehensive POD model for eddy current NDE. Eddy current methods of nondestructive testing are used widely in industry to inspect a variety of nonferromagnetic and ferromagnetic materials. The development of a comprehensive POD model is therefore of significant importance. The model incorporates several sources of variability characterized by a multivariate Gaussian distribution and employs finite element analysis to predict the signal distribution. The method of mixtures is then used for estimating optimal threshold values. The research demonstrates the use of a finite element model within a probabilistic frame-work to the spread in the measured signal for eddy current nondestructive methods.
Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 19-24 Jul. 1992. Vol. 12B, pp.2365-2372. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1993) ISBN 0- 306-44483-6 This paper presents a comprehensive POD model for eddy current NDE. The model incorporates several sources of variabilities characterized by a multivariate Gaussian distribution and employs the finite element method to predict the signal distribution. The paper demonstrates the use of a finite element model within a probabilistic framework to predict the spread of the measured signal for eddy current nondestructive methods. Using the signal distributions for various flaw sizes the probability of detection curves for defects of varying widths have been computed. Results demonstrating the value and utility of the approach are presented. In contrast to experimental POD models, the cost of generating such curves is very low and complex defect shapes can be handled very easily. The results are also operator independent.
55778 Gerasimnv, V.G.; Malov, V.M.; Efraimov, L.Y.; Evdokimov, P.A.
Eddy-current inspection of carbon components Russian Journal of Nondestructive Testing, Vol. 29, No. 9, pp. 643-649 (May 1994) Problems of eddy-current inspection of carbon-carbon composites are considered. A method is described for approximate calculation of signals of a superposed eddy-current transducer from defects of the crack type. The results are reported from experimental studies of samples of carbon-carbon composites with and without defects. The block diagram is given along with a description of the software for a device for detecting surface cracks in products made of those composites. 54987
54757 Placko. D.; Dufour, I. Eddy current sensors for nondestructive inspection of graphite composite materials 27th Annual Meeting of the Industry Applications, Houston (United States), 4-9 Oct. 1992. Vol. 2, pp. 1676-1682. IEEE (1992) ISBN 078030634 1 A system using eddy current sensors for nondestructive evaluation of graphite composite plates is described. First, the basic physical principle of measurements with this kind of sensors is recalled. Then, an analytical model of the relationships between the properties of the object approached in the sensitive area of the sensor and the induced variation of signal is presented: in our case, the interesting properties are the distance between the sensor and the plate, and its local conductivity. In the second part, the inversion of this model is discussed in view to extract the useful data from the sensor signal. This method is then illustrated in the case of a graphite composite plate on which a mechanical constraint is applied. The inspection process consists in scanning the sensor above the surface of the sample, and computing in each point either values of distance or conductivity. Both these results presented at successive steps of structure damages show simultaneously the surface deformations and the internal defects in the sample, demonstrating the interest of our method.
Delsarte, G.; Levy, R.
Mascotte, an analytical model for eddy current signals I I th International Conference and Exhibits on NDE in the Nuclear and Pressure Vessel Industries, Albuquerque, New Mexico (United States). 30 Apr. - 2 May 1992. pp. 283-288. ASM International (1992). ISBN O-87170- 446-3 Mascot@ a physical model including simple approximations, is applied to discontinuities such as wall-losses, inclusions and complex defects on a non ferromagnetic tube examined with a bobbin coil probe. The eddy current signal is described by analytical formulations which take into account the environmental parameters: tube dimension, probe design, excitation frequency, and physical features of the defect. Moreover, the simulated signal can be combined with the actual signal from a known discontinuity such as a supportplate. 54986 c.
Coutanceau-Monteil,
N.; Billy, F.; Cahouet. J.; Chavant.
54543 Wincheski, B.; Fulton, J.P.; Nath, S.; Namkung, M.; Simpson, J. W.
A complementary approach of 2D and 3D modeling for the understanding and the design of pulsed eddy current probes 1I th International Conference and Exhibits on NDE in the Nuclear
Self-nulling eddy current probe for surface and subsurface flaw detection Materials Evaluation, Vol. 52, No. 1, pp. 22-26 (Jan. 1994)
and Pressure Vessel Industries, Albuquerque, New Mexico (United States), 30 Apr. - 2 May 1992. pp. 273-276. ASM International (1992). ISBN O-87170- 446-3 In order to improve Pulsed Eddy Current (PEC) techniques for detecting and sizing subsurface cracks in non magnetic metals, numerical modelling and experiments are performed. The impulse response of the probe is simulated with a 2D finite element code and compared with experimental data. It is shown that 2D modelling for both axisymetrical and plane representations doesn’t simulate the interaction of the PEC probe with a subsurface plane electron-discharge machined (EDM) slot. On the contrary, 3D modelling performed with the TRIFOU code confirms experimental observations such as the. directivity of the probe and the tip effect from the slot. The sensitivity of the signal to the depth and orientation of the flaw and to the location and orientation of the receiving coil (i.e., various probes) is discussed. It is thus possible to size the length of the flaw through tip detection.
An eddy current probe. that provides a null-signal in the presence of unflawed material without the need for any balancing circuitry has been developed at NASA Langley Research Center. This capability reduces set-up time, eliminates tester configuration errors, and decreases instrumentation requirements. The probe is highly sensitive to surfacebreaking fatigue cracks, and shows excellent resolution for the measurement of material thickness, including material loss due to corrosion damage. The presence of flaws in the material under test causes an increase in the extremely stable and reproducible output voltage of the probe. The design of the probe and some examples illustrating its flaw detection capabilities are presented. 54283
Combustion Engineering Inc.; (Edwards, L.J.)
Method for detecting flaws in a steam generator tube using a flexible eddy current probe having coil band switching U.S. Patent No. 5,256,966 (26 Oct. 1993) A method of detecting flaws in a tube is described. It has a probe assembly with a probe heat with two sets of coils. A bank switch allows switching between the coils. Output signals are received which are transmitted over conductors from the coils, representative of the flaws.
54983 Krzywosz, K.; Henry, G.; O’Brien, J. Eddy current pit sizing techniques for copper alloy tubing 11th International Conference and Exhibits on NDE in the Nuclear and Pressure Vessel Industries, Albuquerque, New Mexico (United States), 30 Apr. - 2 May 1992. pp. 345-352. ASM International ( 1992). ISBN O-87170- 446-3 Copper based alloy tubing utilized in power plant heat exchangers is susceptible to pitting on the inside tube surface. Localized pitting is most damaging since it reduces load-carrying capacity and increases stress concentration by creating holes in the tube wall. To assesstubing integrity,
54222
Sakamoto, T.
Remote
field
ferromagnet.ic Abstract) Journal of
174
eddy
current
heat- exchanger
for (In Japanese:
examination tubes
U-shape English
JSNDI, Vol. 42, No. 10, pp. 563-569 (Oct. 1993)
N DT Abstracts It comprises several coils inserted axially into the metal pipe including an exciting coil for receiving an alternating current and generating field eddy current signals and two receiving coils. A differential signal representing the vectorial difference between eddy current signals from the two coils is obtained. The phase of this signal is compared to a reference signal to determine the presence of flawed regions of the pipe based on the cumulative offset amplitude.
The remote field Eddy current technique (RFECT) is the unique potential method capable of inspecting U-shape ferromagnetic heatexchanger tubes. Basic experimental study on RFECT has been part of 45 mm in minimum radius. While: higher test frequency generates larger defect signal, it causes the rapid increase of magnetic noise in general which is observed in conventional eddy current testing. Based on experimental work, it is proved that both tube wall and electromagnetic characteristics determine the optimum test frequency. in which defects can be detected with high signal to noise ratio. In comparison of defect detectability in the straight tube part, inner coil eddy current method with strong magnetizing ability is superior to RFECT method in the case of thin wall thickness less than 2 mm. Therefore it is necessary for high accurate inspection to use both testing methods.
53284
U.S. Patent No. 5,184,070 (2 Feb. 1993) An eddy current test instrument with a rotary head with at least two test heads is described. The heads include eddy current test probes mounted on a circular track to scan a part. The defect signals are processed and evaluated.
54036 Hedengren, K.H.; Hurley, D.C.; Kornrumpf, W.P.; Young, J.D.; Sutton, G.H.
53282 Young, J.D.; Hedengren, K.H.; Hurley. D.C. Method and apparatus for a multi-channel multi-frequency data acquisition system for nondestructive eddy current inspection testing
An array system for fast, sensitive eddy current inspections ASNT 1993 Fall Conference and Quality Testing Show. NDT: A Partner in Engineering Innovation, Long Beach, California (United States), 8-12 Nov. 1993. pp. 51-53. ASNT (1993) A unique eddy current array system for non-destructive testing has been developed by GE. Conformable sensor arrays, multiplexing multichannel data acquisition electronics, hybrid electronic/mechanical scanning for rapid complete surface coverage, and signal/image processing for automatic flaw detection are key features of the system. The system, which is the first of its kind in the world, has been in use for production inspections of turbine disk dovetail slots at a GE manufacturing plant since September 1992. The inspection coverage rate is more than an order of magnitude faster than with the previous single probe process, while maintaining required defect sensitivity.
54027
U.S. Patent No. 5,182,513 (26 Jan. 1993) An eddy current inspection apparatus for detecting flaws in a conductive surface. is described. It consists of several eddy current probes: a means of automatically scanting the surface and multiplexing and demodulating the measurement signal. It also has a means for automated image processing of the digital components of the signals. 53027
Alabama Univ., in Huntsville, (United States), N93-12875/9/GAR, 22pp. (18 Jul. 1991) The use of eddy current techniques for characterizing flaws in graphite-based filament-wound cylindrical structures is described. A major emphasis was also placed upon incorporating artificial intelligence techniques into the signal analysis portion of the inspection process. Developing an eddy current scanning system using a commercial robot for inspecting graphite structures (and others) was a goal in the overall concept and is essential for the final implementation for the expert systems interpretation.
Bowler, J.R.; Harrison, D J.; Norton, S.J.
Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 19-24 Jul. 1992. Vol. 12A, pp. 243-249. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1993). ISBN O-306-44483-6. This paper is mainly concerned with computational issues, though we shall briefly touch on analytical questions concerning the nature of the gradients. The object of the present inversion study is a crack with zero opening yet acting as a perfect barrier to electric current. The shape of this ideal crack is described by a flaw function which expresses the position of the crack edge as the equation of a line. Once the equation of the line has been found, the length, maxima depth and the geometry of the crack profile can be deduced.
53527
Atherton, D.L.; Mackintosh, D.D.; Sullivan, S.P.; Duhois. 53024 J.M.S.; Schmidt, T.R.
Remote-field eddy current signal representation Materials
Vol. 5 1, No. 7, pp. 782-789
(Jul. 1993)
scope monitor displays customarily used for conventional exploring coil ET probes in tubes. We then present the normalized voltage plane and monitor displays that are most appropriate for RFEC probes. We discuss the similarities and differences between the preferred monitor displays.
Sakamoto, T.; Fujiwara, H.
of
53022
Stepinski, T.: Maszi, N.
Conjugate spectrum filters for eddy current signal processing
(1993) Magnetic saturation is applied to ferromagnetic tubes inspected by the encircling or inner coil because suppressing magnetic noise is important for the eddy current testing technique. Eddy current signal characteristics in magnetically saturated tubes are different from those in nonmagnetic tubes. In ferromagnetic tubes, defect signal phase angle is not useful for estimating defect depth because it does not depend on the defect depth. In this paper, numerical eddy current analysis has been done in order to explain the relationship between the defect depth and the phase angle in magnetically saturated tubes.
Materials Evaluation, Vol. 5 1, No. 7, pp. 839-844 (Jul. 1993) The paper addresses the problem of detection and classification of material defects during eddy current inspection. Digital signal processing algorithms for detection and characterization of flaws are considered and a new type of filter for classification of eddy current data is proposed. In the first part the signal processing blocks used in modem eddy current instruments are presented and analyzed in terms of information transmission. A method is then presented which employs two-dimensional conjugate spectrum filters (CSFs) that are sensitive both the the phase angle and the shape of the eddy current responses.
Cueman, M.K.; Hurley, D.C.; Tuck, P.B.
52753
Method a’nd apparatus for making spatially correlated eddy current measurements
Mackintosh, D.D.; Atherton, D.L.; Puhach, P.A.
Through-transmission equations for remote-field eddy current inspection of small-bore ferromagnetic tubes
U.S. Patent No. 5,175.498 (29 Dec. 1992)
Materials
An apparatus for measurin,g flaws in an object having both erratic and net motions is described. It has a means for sensing the motion of the object and detecting any flaws. The flaw signal is corrected to erratic motion by a triggered (A/D) converter. 53305
Evaluation,
Here we first of all summarize the impedance plane representation and
Research in Nondestructive:Evaluation, Vol. 5, No. 2, pp. 135-146
53323
Workman, G.L.
Automated eddy current analysis of materials. Final report
Inversion of eddy current probe impedance data for crack reconstruction
Numerical analysis for eddy current characteristics magnetically saturated ferromagnetic tubes
Besendorfer, H.; Stritzke, G.; Haditsch, F.
Eddy-current defect test instrument with multiple test probes and one distance probe
Evaluation,
Vol. 5 1, No. 6, pp. 744-748
(Jun. 1993)
Experimentally measured deviations from skin depth theory are described. A theoretical investigation is made of through-transmission for a cylindrical wave impinging on a conducting tube. The cylindrical throughtransmission equations agree well with RFEC data. The application 0: the new equations to RFEC defect signal analysis is discussed. A case study of an RFEC scan of a metal loss defect is described. The through-transmission equations were found to hold at the defect. However, the RFEC scan data deviated slightly from the value predicted by the through-transmission equations. The deviation was attributed to a perturbation of the field on the outside of the pipe caused by the defect, an effect no considered in a
Hosohara. Y.; Suzuki, K.; Fujiwara, S.; Kawahe, T.
Remote field eddy current flaw detector for metal pipes having a pair of receiver coils providing a differential offset amplitude signal U.S. Patent No. 5,210,492 (I I May 1993)
through- transmission analysis.
A remote field eddy current detector for detecting flaws in a metal pipe.
175