Pulsed Eddy Current Nondestructive Testing Research Articles

Quantitative evaluation of crack depths and angles for pulsed eddy current non-destructive testing

Cracks with inclination angles may potentially cause damage to a larger region in the tested structures. Their characterization, in terms of depth and angle, is therefore paramount for ensuring the integrity of the specimen under test. This study extracts features from Pulsed eddy current (PEC) signals obtained in a linear scan, perpendicular to the simulated surface cracks. The novel features extracted, termed skewness, LLS and LSmax, are capable of defining crack depth and inclination angles simultaneously. Multiple linear regression (MLR) was built to perform depth prediction, and the pre-determined depths were used in the hierarchical linear model (HLM) for angle prediction. The results were then compared with depth and angle prediction using artificial neural network (ANN). Better reliability of the ANN model with recorded RMSE of 0.198 mm and 2.903° in depth and angle prediction are highlighted. ANN is favourable in handling simultaneous prediction of crack depth and inclination angles, when using interdependent features. Meanwhile, HLM is still approved as a technique to provide a preliminary understanding of the crack parameters.

Pulsed Eddy Current Nondestructive Testing for Defect Evaluation and Imaging of Automotive Lightweight Alloy Materials

Rapid and accurate damage detection of magnesium-aluminum alloy, which is an important material for automotive lightweight, is of great significance. Pulsed eddy current (PEC) is an effective electromagnetic nondestructive testing and evaluation (NDT&E) technique for metal materials. Metal loss evaluation and imaging are one of the most important steps in quality control and maintenance of key components of automobiles. A PEC method based on a rectangular excitation coil and an axial parallel pickup coil is proposed and investigated for the purpose of metal loss evaluation and imaging. Metal loss type of defects with different sections is designed and detected using line scanning technique and C-scan imaging in two scanning directions. Experimental results have illustrated that metal loss depth can be estimated effectively by the peak amplitude of PEC A-scan response. Then, the quantification information of metal loss depth is preliminarily obtained based on the linear fitting equation. Consequently, metal loss evaluation is realized by line scanning peak waves and C-scan pseudo 3D images. At last, the sensitivity comparison shows that the metal loss can be detected in both directions. The proposed method is an effective approach to evaluate the image surface-breaking metal loss in automotive lightweight alloy materials.

Effects of Coil Diameter in Thickness Measurement Using Pulsed Eddy Current Non-destructive Testing

Non-destructive testing (NDT) techniques are used in industry to evaluate the properties of a material, component or structure without causing any permanent damage. Among the techniques, pulsed eddy current (PEC) NDT is regarded as a new technique where a broadband pulse excitation is used, as opposed to single frequencies employed in conventional eddy current NDT. In this study, a 2D axisymmetric electromagnetic model of a PEC probe has been developed and it has been used to study the effects of the excitation coil diameter on the performance of PEC probes in sample thickness measurement. A PEC system has also been built to validate the model. Aluminium plates are used as the sample and they can be stacked up to replicate thickness from 1 mm to 10 mm. The results show that there is a very good correlation between the simulation and experimental results, with an average error of less than 10%. The results also suggest that the larger the diameter of the excitation coil, the deeper the penetration and therefore the larger the thickness measurement range. It has also been shown that although the larger diameters have deeper penetration, the smallest diameter has the highest sensitivity if normalization is not used. These conclusions indicate that coil diameter is an important parameter in a PEC probe design for thickness measurement applications.

Erratum to: Pulsed Eddy Current Non-destructive Testing and Evaluation: A Review

Erratum to: Pulsed Eddy Current Non-destructive Testing and Evaluation: A Review

Investigation of rectangular differential probes for pulsed eddy current non-destructive testing

Investigation of rectangular differential probes for pulsed eddy current non-destructive testing

펄스 와전류 비파괴검사의 원리

펄스 와전류 비파괴검사의 원리

Study on Pulsed Eddy Current Nondestructive Testing Technology for Pipeline Corrosion Defects Based on Finite Element Method

According to the principle and the type of the oil pipeline corrosion, we use the square wave of wide spectrum, strong signal transmission capability and a certain duty ratio as the excitation source of the pulsed eddy current. The finite element analysis software ANSYS is used to establish a three-dimensional finite element model of the pipeline corrosion defects by applying the boundary conditions of square wave excitation to simulate the distributions of current and induced magnetic field in the pipeline under various defect volumes. It can solve the induced voltage variation with time on detection coil, and can accomplish the finite element analysis and the nondestructive testing about the pipeline internal corrosion defects with the insulation layer and the protection layer. The results of the study show: When there is no corrosion defect in the pipeline, the electric current in the pipeline is basically even distribution. The magnetic field is distributed for the symmetrical vortex shape from head to foot, and it has not obviously gather phenomenon. When there are some corrosion defects in the pipeline, the electric current forms partial symmetrical vortex shape in both sides of the corrosion defect, and it is obviously assembled in the defect place. The simulation results of the different size defects show that the maximum magnetic field strength and the maximum current value increase with the defect depth increasing, while the output voltage decreases with the defect depth increasing. By extracting the induced voltage signals on the detection coil in a certain excitation condition, the quantitative detection of the pipeline corrosion defects can be achieved.

Defect classification in two-layer complex structures based on spectrum analysis of pulsed eddy current

Pulsed eddy current (PEC) testing is an increasingly emerging non-destructive testing and evaluation (NDT&E) technique. Defect classification is one of the most important steps in PEC defect characterisation. It is difficult to classify defects in two-layer complex structures of ageing aircraft or other complex structures. As a result of taking a square-wave signal as excitation, the PEC response signals contain rich information in the frequency domain. In this paper, two defect classification methods based on spectrum analysis are proposed to classify the defects in two-layer complex structures. Method 1 is based on direct frequency spectrum analysis, while method 2 is by means of differential frequency spectrum analysis. Experimental tests and blind tests are carried out and the results show that the different classes of defect can be identified and classified effectively. The lift-off test results show that the lift-off effect can be restrained by the proposed method. The frequency spectrum method has a good prospect in the field of PEC non-destructive testing and evaluation.

Reduction of lift-off effect for pulsed eddy current NDT based on sensor design and frequency spectrum analysis

Pulsed eddy current (PEC) nondestructive testing (NDT), as for most of EC techniques, is prone to lift-off effect, which influences the interpretation and quantification of flaw. A new technique for reducing the lift-off effect and quantifying flaw based on sensor design and frequency spectrum analysis is proposed. The technique exploits the self-differential feature of the sensor and the broadband frequency spectral content of pulsed excitation. Results show that the lift-off has been significantly reduced and the precision of quantification of flaw has been improved.

Feature extraction and selection for defect classification of pulsed eddy current NDT

Pulsed eddy current (PEC) is a new emerging nondestructive testing (NDT) technique using a broadband pulse excitation with rich frequency information and has wide application potentials. This technique mainly uses feature points and response signal shapes for defect detection and characterization, including peak point, frequency analysis, and statistical methods such as principal component analysis (PCA). This paper introduces the application of Hilbert transform to extract a new descending feature point and use the point as a cutoff point of sampling data for detection and feature estimation. The response signal is then divided by the conventional rising, peak, and the new descending points. Some shape features of the rising part and descending part are extracted. The characters of shape features are also discussed and compared. Various feature selection and integrations are proposed for defect classification. Experimental studies, including blind tests, show the validation of the new features and combination of selected features in defect classification. The robustness of the features and further work are also discussed.

Identification of corrosion fringe in pulsed eddy current nondestructive testing

It is difficult to accurately identify corrosion fringe in nondestructive testing (NDT),which will directly influence the effect of corrosion imaging.Array pulsed eddy current (APEC) is used to detect corrosion.With the purpose of overcoming the problem of low identification accuracy in conventional NDT which only extracts features in the time domain,on the basis that PEC has a broadband frequency,features are extracted in both time and frequency domains.A method based on principal component analysis (PCA) is proposed to enhance the accuracy of identification of corrosion fringe,the agreement between theory and experiment shows that the present method is correct.

Flaws characterization with pulsed eddy currents NDT

In this paper, we present a method for characterizing flaws in metallic structures with pulsed eddy current nondestructive testing (NDT). In a first step, we explain why we have chosen a deconvolution method based on conjugate gradient algorithm (CG). After a description of this method and the way it is used for characterization, a validation is performed by coupling it with a 2D FEM (2 dimensional finite elements method) package. The obtained results are compared with experimental measurements. In the last step, a parametric study on parameters obtained with the impulse response gives an estimation of the dimensions of the flaw.