Eddy Current Inspection Research Articles

Improved eddy-current inspection for steam generator tubing : Dodd, C.V.; Pate,.I.R. Oak Ridge National Lab., Tennessee (United States), DE91002860/GAR, 19 pp. (1990)

Improved eddy-current inspection for steam generator tubing : Dodd, C.V.; Pate,.I.R. Oak Ridge National Lab., Tennessee (United States), DE91002860/GAR, 19 pp. (1990)

Fundamental studies of remote field eddy-current inspection : Hoshikawa, H.; Koyama, K.; Koido, J.; Ishibashi, Y. 9th International Conference on Nondestructive Evaluation in the Nuclear Industry, Tokyo (Japan), 25–28 Apr. 1988. pp. 339–344. Edited by K. Iida, J.E. Doherty and X. Edelmann. ASM (1988)

Fundamental studies of remote field eddy-current inspection : Hoshikawa, H.; Koyama, K.; Koido, J.; Ishibashi, Y. 9th International Conference on Nondestructive Evaluation in the Nuclear Industry, Tokyo (Japan), 25–28 Apr. 1988. pp. 339–344. Edited by K. Iida, J.E. Doherty and X. Edelmann. ASM (1988)

Improved eddy-current inspection for steam generator tubing. Progress report for period January 1985–December 1987 : Dodd, C.V.; Deeds, W.E.; McClung, R.W. Oak Ridge National Laboratory., Tennessee (United States), ORNL-TM- 11389, NUREG-CR-5478, 37pp. (Jan. 1989)

Improved eddy-current inspection for steam generator tubing. Progress report for period January 1985–December 1987 : Dodd, C.V.; Deeds, W.E.; McClung, R.W. Oak Ridge National Laboratory., Tennessee (United States), ORNL-TM- 11389, NUREG-CR-5478, 37pp. (Jan. 1989)

Finite element modeling of conducting shells for eddy current NDE problems using "impedance-type" interface conditions

A 3D finite element scheme is developed to calculate eddy current probe responses (impedance or induced emf changes of coils) due to conducting shells in eddy current NDE (nondestructive evaluation) problems. These problems are related to the eddy current inspection of copper and magnetite deposit zones of steam generator tubing in PWR atomic power plants. The finite element scheme uses impedance interface conditions to model the deposit shells and calculates the probe responses by performing integrals over the shell surfaces, thereby ensuring high accuracy even if the probe signal is very small. Two benchmark arrangements are investigated. One, which has an analytical solution, is a conducting thin plate with an impedance probe. The other is a stainless steel tube with a copper shell attached to its outer surface and scanned by a transmitter-receiver probe. In both problems, the calculated probe responses show good agreement with the analytical and experimental data.

The Role Of Grain Noise In Eddy Current Inspection Of Titanium Alloys

ABSTRACTThis paper discusses the role electrical anisotropy plays in the structural integrity assessment of polycrystalline titanium alloys from the standpoint of fatigue crack detection and the related issue of microstructural noise. In eddy current inspection of noncubic crystallographic classes of polycrystalline metals the electric anisotropy of individual grains produces an inherent microstructural variation or noise that is very similar to the well-known acoustic noise produced by the elastic anisotropy of both cubic and noncubic materials in ultrasonic characterization. The presented results demonstrate that although the electrical grain noise is detrimental in eddy current nondestructive testing for small flaws, it can be also exploited for characterization of the microstructure in noncubic polycrystalline materials such as titanium alloys in the same way acoustic grain noise is used for ultrasonic characterization of the microstructure in different materials.

96/06036 An integrated signal processing and neural networks system for steam generator tubing diagnostics using eddy current inspection

96/06036 An integrated signal processing and neural networks system for steam generator tubing diagnostics using eddy current inspection

An integrated signal processing and neural networks system for steam generator tubing diagnostics using eddy current inspection

The primary purpose of this research was to develop an integrated approach by combining information compression methods and artificial neural networks for the monitoring of plant components using nondestructive evaluation (NDE) data. Specifically, data from eddy current inspection of steam generator tubing were utilized to evaluate this technology. The focus of the research was to develop and test various data compression methods (for eddy current data) and the performance of different neural network paradigms for defect classification and defect parameter estimation. Feedforward, fully-connected neural networks, that use the back-propagation algorithm for network training, were implemented for defect classification and defect parameter estimation using a modular network architecture. A large eddy current tube inspection database was acquired from the Metals and Ceramics Division of Oak Ridge National Laboratory (ORNL). These data were used to study the performance of artificial neural networks for defect type classification and for estimating defect parameters. Most of the study was made using the NeuralWorks Professional II/Plus software. A PC-based data pre-processing and display program was also developed as part of an expert system for data management and decision making. The results of the analysis showed that for effective (low-error) defect classification and estimation of parameters, it is necessary to identify proper feature vectors using different data representation methods. The integration of data compression and artificial neural networks for information processing was established as an efficient technique for automation of diagnostics using nondestructive evaluation methods.

Effective probe response calculation using impedance boundary condition in eddy current NDE problems with massive conducting regions present

A 3-D finite element scheme is described for calculating probe responses in eddy current nondestructive evaluation (NDE) problems if massive conducting regions with small penetration depth are in the vicinity of the host specimen. These problems are related to the eddy current inspection of the tube support plate or tube sheet zones in PWR steam generator tubing. Recently, an efficient finite element scheme has been introduced to calculate the probe responses outside these zones. As a sequel to that work, the authors extend the technique for the tube support plate and the tube sheet zones. They use impedance boundary conditions (IBC) on the surface of the massive conductors and evaluate the probe responses due to these components by performing an integral over these IBC surfaces, thereby ensuring the same accuracy as in the previous work for the flaw signals. Benchmark problems-models of tube support plate zones with defects-have been measured and analyzed. The calculated probe responses show good agreement with the experimental data.

Eddy-current inspection of shuttle heat exchanger tube welds : Dodd, C.V.; Scott, G.W.; Chitwood. L.D. Oak Ridge National Laboratory, Tennessee (United States), DE90001335/GAR, 17 pp. (1989)

The goal of this project was to develop the system necessary to demonstrate in the laboratory that an eddy current system can inspect the tubes and welds described, screening for the existence of flaws equal in size to, or larger than, the target flaw. The laboratory system was to include the probe necessary to traverse the tubing, the electronics to drive (i.e., electrically excite) the probe and receive and process signals from it, a data display, data recording, and playback devices, and microprocessor software or firmware necessary to operate the system.

Characterisation of Low Energy Impact Damages in Composites

A non-destructive examination technique using an electromagnetic testing method has been developed for the inspection of reinforced carbon fibre materials. Damage detection was performed on a total of 53 low energy impacts (from 0.5 to 10 Joules) which were induced in realistic samples supplied by the aerospace industry. The eddy-current technique employed was proven very accurate and inherently reproducible in the detection of low energy impact damages in carbon reinforced materials. These damages were below the detection threshold of other conventional NDT methods such as ultrasonic, infrared thermography and radiography. A statistical analysis, making use of probability of detection curves (POD) and receiver operating characteristic curves (ROC) has been performed in order to evaluate the performance of different inspection systems. Computer visualisation facilities were used to locate and quantify impacts on carbon materials. The technique was also proven very efficient to assess the structural integrity of CFRP and GFRP helicopter rotor blades. If correctly applied, eddy current inspection will certainly enhance the quality and efficiency of non-destructive examinations and improve the level of quality and safety required by the aerospace industry.

Application of a diffusion-to-wave transformation for inverting eddy current nondestructive evaluation data

A transformation from diffusion fields to wave fields is examined as an approach to inverting eddy current nondestructive evaluation (NDE) data. An analytic inversion to the transformation is used as a means to gain insight into robustness issues associated with the method. A discretized version of the transformation is utilized to solve a 1-D inverse problem with a direct wave-based approach. Because the transformation lacks robustness, two regularization schemes are used to stabilize the inversion, which are themselves enhanced by an averaging algorithm. The technique is shown to be unstable when applied to sources which are not ideal impulse functions, in which case the transformation can be stabilized via low-pass filtering. The transformation is not useful with time-harmonic sources and is therefore limited to pulsed eddy current inspections.

Experiments in contact control

The implementation, experimentation, and application of contact control schemes for a 7-DOF Robotics Research arm is presented. Three types of control schemes are presented: compliance cntrol, force control, and dual-mode control. This presentation is concluded with the application of the proposed schemes to perform a contact-based eddy-current inspection task.

Longitudinal AC Interactions with Axial Slits in Steel Pipes

Abstract The Remote Field Eddy Current (RFEC) nondestructive inspection technique uses low frequency AC and through wall transmission to inspect pipes and tubes from the inside. In steel pipes, it has generally greater sensitivity to circumferential rather than axial slits because the perturbation of magnetic fields orthogonal to slits dominates. Circumferential AC magnetic fields, generated by passing AC axially along a steel pipe from an external supply, have therefore been tested in order to give greater sensitivity to axially aligned cracks characteristic of stress corrosion cracking in pipelines. Anomalous source missing magnetization defect models suggest that, as slit widths are reduced, the importance of magnetic interactions is reduced until eddy current interactions predominate. This suggests that, for very fine axial cracks, true RFEC geometry, which gives circumferential eddy currents, will give stronger signals than circumferential AC magnetic fields.

Expanding the capabilities of eddy-current inspection of pipes with a wide range of diameters and grades of steel

The circuit design of the new VD-40P eddy-current flaw detector is described. The salient features of the detector are considered and its capabilities of measuring flaw sizes and for standardization of metrological characteristics are explained.

Eddy-current inspection of sheet of nonmagnetic material by superposed transducer excited by pulsed current with nonideal shape : Sapunov, V.M.; Beda, P.J. Soviet Journal of Nondestructive Testing, Vol. 27, No. 10, pp. 743–750 (Jun. 1992)

Eddy-current inspection of sheet of nonmagnetic material by superposed transducer excited by pulsed current with nonideal shape : Sapunov, V.M.; Beda, P.J. Soviet Journal of Nondestructive Testing, Vol. 27, No. 10, pp. 743–750 (Jun. 1992)

Integrity of VVER steam generator tubes

The eddy-current inspection is applied to Vitkovice to non-destructive testing of the steam generator tubes. The steam generator tube specimens, 16 mm by 1.5 mm, are made of AISI 321 steel with stress corrosion cracks. They were tested by the single-frequency eddy current inspection method. Samples with known flaws were metallographically sectioned to determine the actual extent of corrosion degradation. The relation between measurement of the tube wall corrosion damage and actual extent of corrosion attack or stress corrosion cracking (SCC) was determined. Pressurized specimens with machined notches of various geometries were tested up to failure. The effect of flaw depth and length on the burst pressure were evaluated.

Anomalous magnetic source defect modelling

Defect-induced field perturbations occurring during electromagnetic testing of ferromagnetic material can be modelled as combinations of anomalous eddy current and missing magnetization sources. At low frequencies, such as are used in Remote Field Eddy Current (RFEC) inspection of steel tubes, the anomalous magnetization defect sources dominate and give strong responses to circumferential slits orthogonal to the axial magnetic field. Here we present the results of finite element calculations and computer animations of the time-varying fields from a missing magnetization model of a slit defect. These are compared with the defect-induced anomalous field patterns obtained by phasor vector subtraction of calculations for slit defect and defect-free problems. It is noted that the ferromagnetic material in which the defect is located must be included in the missing magnetization model.

Application of eddy current testing inspection to the first wall of fusion reactor with wavelet analysis

The eddy current testing (ECT) technique is introduced for the non-destructive evaluation of the first wall of a fusion reactor. With the aim of in-service inspection of the first wall, a method to evaluate cracks in the first wall is studied theoretically utilizing impedance signals and magnetic field data obtained from ECT. From the impedance signals, the depth of the cracks is determined using an impedance—depth calibrating curve. Since an impedance signal may be caused by some undesired factors as well as by a crack, an approach to extracting crack information from such a composite signal is developed using wavelet analysis. For reconstruction of the surface shape of the cracks, the magnetic field data are inverted into the distribution of the current vector potential T by solving an inverse problem and the wavelet coefficients of T are calculated to characterize the shape of the cracks. It is shown that the combination of ECT and wavelet analysis provides an efficient method of non-destructive evaluation of cracks in the first wall.

Reliability of automatic eddy-current equipment with a rotating magnetic field

This paper presents a method for estimating the reliability of eddy-current nondestructive inspection by using the rotating magnetic field method. The results of the inspection are considered as memory-less stochastic processes, with the possibility of representation in a bi-dimensional space: ‘good product’ and ‘bad product’. The general formulae are calculated by using the master equation for the time behaviour of the probabilities, the numerical data used for results estimation being obtained by means of an automatic eddy current installation with rotating magnetic field. The samples used had 20 μm, 40 μm and 98 μm deep artificial faults, and the control speed ranged between 0.05 and 1 m s −1.

Remote field eddy current inspection

The Remote Field Eddy Current (RFEC) technique uses an internal probe to inspect conducting tubes nondestructively. A coaxial solenoidal exciter, energized with low frequency AC, and detector coils near the inside of the pipe wall are separated by about two pipe diameters to obtain through wall transmission and equal sensitivity to defects on the outside or inside of the pipe wall. Calculation methods are outlined and the voltage plane polar plot signal representation for defect measurement is described. Slit defect interactions in ferromagnetic and non-ferromagnetic tubes are discussed. Defect-induced anomalous fields are interpreted in terms of anomalous source eddy current and missing magnetization defect models. The use of computer animations to represent the time variations of high resolution field measurements and calculations is described.