Pulsed Eddy Current Non-destructive Evaluation Research Articles

Pulsed Eddy Current NDE of Groove Dimensions by Inversion With Simplex Method Associated With Coupled Electric Circuits Method

This paper describes a pulsed eddy current nondestructive evaluation of an annular groove dimensions using a simplex inversion method associated with a semianalytical direct model, in axisymmetric case. The proposed semianalytical formulation, used for direct calculations, is developed from coupled electric circuits modeling. It uses the current excitation allowing the determination of the sensor voltage. The feature of the variation of voltage provides information on the electromagnetic and geometrical properties of the device. The transient sensor voltage is then calculated, allowing the evaluation of the groove dimensions of the considered work piece. The peak's amplitude and the zero and peak crossing times are used to determine these properties.

Analytical approach to pulsed eddy current nondestructive evaluation of multilayered conductive structures

This paper proposes an analytical approach that can describe the Pulsed Eddy Current Testing (PECT) of stratified conductive structures by a single air-coil used for detecting and sizing of metal loss due to interlayer corrosion. Specifically for a single air-cored coil above a multilayered conductive structure, the coil impendance response of the cylindrical eddy-current probe is calculated based on the truncated region eigenfunction expansion (TREE) method using the generalized matrix coefficients in series form. Analytical modeling of pulsed eddy current is developed using the Fourier series for multilayered conductive structures. A simulation study is carried out for demonstrating the capability of the proposed approach for sizing the metal loss in a two-layer specimen. Furthermore, the experiment is set up to confirm the simulating results of the analytical model for multilayered steels. Good agreement between the theoretical results and measured signals is observed.

Time and Frequency Domain Feature Fusion for Defect Classification Based on Pulsed Eddy Current NDT

Pulsed Eddy current (PEC) is an emerging nondestructive evaluation (NDT) technique excited with a broadband pulse that consists of rich frequency information. This technique generally uses the response peak value and peak arrival time to detect and quantify defects, which is not sufficient to achieve enough information associated with flaw quantification. This article introduces the application of empirical mode decomposition and Hilbert transform in extracting a new frequency domain feature from PEC responses. Time and frequency features are combined to enhance the accuracy of defect classification. The validation and robustness of the new feature and the improved classification by experimental studies are presented.

Pulsed eddy current non-destructive evaluation based on coupled electromagnetic quantities method

This paper proposes a semi-analytical model for Pulsed Eddy Current Non-Destructive Evaluation (PEC-NDE) based on the Coupled Electromagnetic Quantities Method (CEQM). The proposed formulation is developed from coupled electric circuit’s approach in which the Crank Nicholson formula is used to derive the transient behavior. The computational model makes use of current excitation allowing the determination of the sensor voltage in the case of an axisymmetric device. The feature of the variation of voltage provides information on the electromagnetic and geometrical properties of the device. So, the second peak of voltage variation (SPVV) and second ratio between the minimum and maximum (RMM2) are used to determine these properties. The proposed model is validated by comparison with Fourier reconstitution obtained from measurements on one hand and with finite element calculations on the other hand. The developed model, associated to an inversion technique, is applied to evaluate the lift-off and the work piece thickness.

A system identification based approach for pulsed eddy current non-destructive evaluation

This paper is concerned with the development of a new system identification based approach for pulsed eddy current non-destructive evaluation. The new approach regards the relationship between the eddy current probe excitation and sensor response as a system, uses the system identification techniques to establish a transfer function model for the system from the excitation and response data, and extracts the features of inspected structures from the identified transfer function model parameters for non-destructive evaluations. The use of the new approach in experimental studies verifies its effectiveness and demonstrates its potential in engineering applications.

Pulsed eddy current transient technique with HTS SQUID magnetometer for non-destructive evaluation

Eddy current non-destructive evaluation (NDE) often uses excitation currents at a fixed frequency, which determines the depth of investigation due to the skin effect. We developed a novel pulsed eddy current NDE technique which potentially may cover a broader depth range, by analyzing the decay of the recorded transient. Eddy currents in the inspected aluminium structures were induced by turn-off of the primary magnetic field pulse in a transmitter coil. The secondary magnetic field created by the induced currents was recorded by an HTS superconducting quantum interference device magnetometer. The quickly decaying early time data of the transient signal corresponds to the information from upper layers of the plate, while the late time data delivers information from deep layers. In order to suppress environmental noise and increase the signal-to-noise ratio, repetitive square-wave pulses were used. The transient response of the plate was recorded in off-time between the transmitter pulses and averaged using a commercial LAPTEM data acquisition unit. Measurements of a crack at different depths in a stacked aluminium sample are presented. The data was analyzed by calculating the apparent conductivity of the sample as a function of depth, a technique often used in Geophysical data interpretation. Possible advantages and drawbacks of this new transient NDE technique are discussed.