Differential Eddy Current Probe Research Articles

Non-Destructive Testing of Carbon Fibre Reinforced Plastics (CFRP) Using a Dual Transmitter-Receiver Differential Eddy Current Test Probe.

Transmitter-receiver (T-R) probes are widely used in the eddy-current testing of carbon fibre reinforced plastics (CFRP). However, T-R probes have the disadvantage of being highly sensitive to lift-off. On this basis, lift-off interference can be eliminated by differential structure. However, due to the electrical anisotropy of CFRP, the detection sensitivity of the side-by-side T-R probe and traditional R-T-R differential probe are greatly affected by the scanning angle, and the probe often needs to scan the sample along a specific path to achieve the ideal required detection effect. To solve these problems, a symmetrical dual-transmit-dual-receive (TR-TR) differential probe is designed in this paper. The detection performance of the TR-TR probe was verified by simulation and experiments. Results show that the TR-TR probe is less affected by the scanning angle and lift-off when used in CFRP defect detection, and has high detection sensitivity. However, the imaging results of the TR-TR probe do not show the defect characteristics straightforwardly. To solve this problem, a defect feature extraction algorithm is proposed in this paper. The results show that the defect feature extraction algorithm can locate and size the defect more accurately and improve the signal-to-noise ratio.

Simulation and Implementation of a High Sensitive Differential Eddy Current Giant Magnetoresistance Probe for Non-Destructive Testing

Simulation and Implementation of a High Sensitive Differential Eddy Current Giant Magnetoresistance Probe for Non-Destructive Testing

Finite Element Modelling of a Reflection Differential Split-D Eddy Current Probe Scanning Surface Notches

Differential eddy current probes are commonly used to detect shallow surface cracks in conductive materials. In recent years, a growing number of research works on their numerical modelling was conducted since the development of analytical or semi-analytical models for such a sensor may be prone to intractable complications. In this paper finite element modelling (FEM) has been employed to simulate the interaction of a reflection differential split-D probe with surface electrical discharge machined (EDM) notches in 3-dimensional (3-D) half-space. In order to attain a better insight into the correct setup of the FEM parameters, a simple multi-turn cylindrical absolute coil has also been modelled. The outcome generated through the simulated scan of this absolute coil over a surface notch in aluminum is validated with existing experimental impedance data taken from the literature. Parameters contributing to reliable FEM simulation results, such as maximum mesh size, mesh distribution, the extent of the surrounding air domain and conductivity of the air are investigated for the 3-D modelling of both absolute and differential probes. This study shows that the simulation results on a commercial reflection differential split-D surface pencil probe closely estimate the experimental measurements of the probe’s impedance variations as it scans three EDM notches having different depths in aluminum. The simulation results, generated by Comsol Multiphysics FEM package (COMSOL I, COMSOL multiphysics reference manual, version 5.3, COMSOL AB, 2018, www.comsol.com), for the cases of absolute and differential probes are checked for their extent of validity.

Adaptive Neuro-fuzzy Inference System Trained for Sizing Semi-elliptical Notches Scanned by Eddy Currents

The present study explores the capability of COMSOL Multiphysics, as a finite element modelling (FEM) tool, to model the interaction between a split-D differential surface eddy current (ECT) probe and semi-elliptical surface electrical discharge machined (EDM) notches. The effect of the small probe’s lift-off and tilt on its signal is investigated through modelling and subsequently, the simulation outcomes are validated using the probe’s impedance measurements. In the next stage, an adaptive neuro-fuzzy inference system (ANFIS) is designed to take the signal features as inputs and consequently, provide the length of the scanned notch as the system’s output. The system is trained by extracted features of thirty model-generated signals obtained from scanning of the same number of semi-elliptical notches by means of the split-D probe. The trained ANFIS is tested afterwards using the measured signals of 3 calibration EDM notches together with 5 model-based ones. A very low average estimation error is observed with regard to the length estimation of the test notches and the accuracy of the length estimation is found to be quite reasonable.

Study, design and manufacture eddy current probes for industry applications

This study is based on the studying, designing and manufacturing of eddy current probes for industry applications. The main tasks of this study include:
 + Describes the overview and classification of eddy current probes (which can be classified into three categories based on the mode of operation: absolute eddy current probe, differential eddy current probe and reflect eddy current probe).
 + Describes the three methods of probe designing and manufacturing (including experimental, analytical and numerical designs).
 + Describes the designing and manufacturing of eddy current probes for industry applications, which based on experimental and analytical methods.
 Based on this study, we have successfully manufactured some current probes (including absolute eddy current probe, differential eddy current probe and reflect eddy current probe) for surface and tube inspections.

On-line rail defect diagnosis with differential eddy current probes and specific detection processing

This paper presents a non destructive evaluation system for rail inspection with a device embedded in a subway train. The difficult operating conditions lead to the design of a specific double-coils and double-frequencies sensor that delivers 8 complementary signals. After the presentation of the technological solution, the paper deals with the detection of minor defects and presents three approaches: the first one is a time heuristic approach, the second one is based on wavelet basis projections, and the last one implements an inverse filtering which allows the transformation of the differential probe outputs into estimated absolute ones. The methods are validated statistically on a labeled defect data set with the help of ROC curves.

Steam Tube Defect Characterization Using Eddy Current Z-Parameters

Steam generator tubing inspections use the impedance of a differential eddy current probe inside a tube as an indication of incipient failure. An axisymmetric finite-element computer code has been developed and utilized to calculate the impedances of the differential probe. The calculated values have been validated by comparison with experimental results. A Z-parameter model for a probe inside a steam tube utilizing differential coils is described, and the response of Z-parameters for the differential probe under various changes in the steam tube configuration is investigated.

Steam Tube Defect Characterization Using Eddy Current Z -Parameters

Steam generator tubing inspections use the impedance of a differential eddy current probe inside a tube as an indication of incipient failure. An axisymmetric finite-element computer code has been developed and utilized to calculate the impedances of the differential probe. The calculated values have been validated by comparison with experimental results. A Z -parameter model for a probe inside a steam tube utilizing differential coils is described, and the response of Z -parameters for the differential probe under various changes in the steam tube configuration is investigated.

Calculations of the flaw signal generated by a differential eddy current probe : Jenkins, S.A.; Bowler, J.R. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 23–28 Jul. 1989. Vol. 9A, pp. 829–835. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990)

Calculations of the flaw signal generated by a differential eddy current probe : Jenkins, S.A.; Bowler, J.R. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 23–28 Jul. 1989. Vol. 9A, pp. 829–835. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990)

The early detection of rolling-sliding contact fatigue cracks

Many previous laboratory studies of the rolling-sliding contact fatigue behaviour of rail steels have been performed on twin-disc wear machines. Usually the discs have been run until spalling occurs due to extensive rolling contact fatigue (RCF) damage; hence metallurgical factors affecting crack initiation and propagation have been difficult to assess. A new wear machine is described, capable of testing large, standard cylindrical discs at high contact stresses with accurate control at low creepages. An eddy current method has been used for the detection of the initial propagation of cracks during an RCF test. The first significant crack or cracks are accurately located by a scanning, high resolution, differential eddy current probe. The method is being used to examine the relationship between rolling-sliding contact fatigue, contact stress, creepage, microstructure and surface events for a range of pearlitic rail steels.

Finite element prediction of differential eddy current probe signals from Fe 3O 4 deposits in PWR steam generators

Finite element analysis techniques have been successfuly applied to the study of eddy current NDT phenomena in axisymmetric test geometries. Major applications of such computer code have related to the design of probes and the gaining of physical insight into just how electromagnetic fields interact with defects. This paper is concerned with an additional application of the code, namely to the simulation of practical testing situations which are too difficult and/or expensive to replicate in a laboratory environment. Numerical experiments are described which simulate the differential eddy current probe response to the build-up and chemical flushing of magnetite in the crevice gap of a PWR steam generator unit. The simulation results agree well with the only experimental data available to the authors and lead to the conclusion that conventional differential eddy current probes should be capable of characterizing crevice gap conditions with respect to the presence of magnetite.

A finite element model for three-dimensional Eddy current NDT phenomena

The defect detection mechanism for eddy current nondestructive testing (NDT) probes is related to the interaction of induced eddy currents in the metal test specimen with flaws and the coupling of these interaction effects with the moving test probe. To date, numerical modeling of these phenomena has been limited to two-dimensional and axisymmetric geometries. A three-dimensional magnetic vector potential finite element formulation for the modeling of eddy current NDT phenomena is described, and the technique is illustrated by predicting differential eddy current probe impedance plane trajectories for flaws in PWR steam generator tubing.

Impedance and mesh structure considerations in the finite element analysis of Eddy current NDT probe phenomena

Differential eddy current probes are used in the nondestructive testing of steam generator tubing for the detection and characterization of defects in the tube wall. Axisymmetric finite element code has been developed to study the associated electromagnetic field/defect interaction phenomena. Alternative forms of probe impedance calculations are examined in this paper together with the effects of mesh structure on the finite element prediction of probe impedance plane trajectories.

Electromagnetic methods of detecting magnetite in PWR steam generators

Corrosion products consisting primarily of magnetite (Fe3O4) in the crevice gap between steam generator tubes and support plates can eventually lead to tube denting and support plate fractures. In order to mitigate this problem, chemical flushing is used to remove the magnetite deposit from the crevice gaps. NDE techniques are needed to measure the effectiveness of this chemical flushing procedure and this paper describes the development and testing of two electromagnetic probes for this purpose. A simple dc variable reluctance probe has been developed under EPRI Project SGPO-S125-1 which gives a measure of crevice gap clearance at eight discrete points around the periphery of the tube. Hall elements are used as the active sensors and the probe drive, and eight-channel signal acquisition is accomplished with ALN 4000 equipment. The alternative electromagnetic approach to the detection of magnetite buildup is to use a conventional differential eddy current probe. Work carried out under EPRI project RP1395-2 has shown that such a probe is also sensitive to the presence of magnetite in the crevice gap.

Prediction of eddy current probe signal trajectories

Development of computer based defect characterization schemes in quantitative eddy current nondestructive testing (NDT) requires an adequate mathematical model capable of describing the complicated interactions between the impressed and induced currents, primary and secondary fields and the flaws in materials. This paper describes a finite element model which predicts the apparent changes in the normalized complex impedance of a differential eddy current probe in axisymmetric NDT configurations. Using this 'numerical model' differential eddy current probe, signal trajectories (as obtained on an eddy-scope screen in actual testing) are predicted for three axisymmetric geometries associated with nuclear power plant steam generators - circumferential I.D. and O.D. slots in an INCONEL tube, and a carbon steel support plate encircling a defect-free tube. Comparison is made between the theoretical and experimental results at a probe excitation frequency of 100kHz. Finite element analysis techniques appear to be well suited to the modeling of eddy current NDT phenomena and for predicting the eddy current probe signal trajectories.