Haoyu Huang

Numerical evaluation of correlation between crack size and eddy current testing signal by a very fast simulator

This paper describes work on the development of a very fast eddy current testing (ECT) signal simulator, and its application to the evaluation of the correlation between cracks and signals. This simulator is developed here based on a reduced magnetic vector potential, edge based finite elements, and the pre-computed unflawed database approach. Using this simulator, three kinds of probes are tested in terms of their linearity and signal to noise ratio.

Inverse analyses for natural and multicracks using signals from a differential transmit-receive ECT probe

This paper describes the inverse analysis in the frame works of a round-robin test for the testing of steam generator tubes by eddy-current testing (ECT). An ECT probe with high space resolution was newly proposed, for the purpose of better and easier crack shape evaluations. This new probe is applied to the round-robin test pieces including natural crack samples and a multicrack sample. Inverse problems of the crack shape reconstructions are solved by a fast forward simulator and the conjugated gradient method. Experimental ECT signals as well as results of reconstructions are shown. Treatments of a natural crack and multicracks are discussed.

Fast signal predictions of noised signals in eddy current testing

This paper describes a new method for the simulation of signals noised by the presence of other materials outside of test materials in eddy current testing. The method developed here, which can treat ferromagnetic materials, is an extension of a pre-computed database approach based on the magnetic vector potential method. It results in much fewer degrees of freedom than those of typical finite element approaches, and the method provides a very fast forward simulator even in the case with ferromagnetic materials.

Design of an eddy-current array probe for crack sizing in steam generator tubes

This paper describes an arrayed multi-coil probe, newly developed for the testing and crack sizing of steam generator tubes by eddy current testing (ECT). The testing speed, the high sensitivity to shallow cracks and the crack sizing are the present requirements in ECT. Because of the multi-coil arrangement, the arrayed probe has a high detection speed around the whole tube, without the need for rotation. It is realized from former studies that knowing the number of cracks, their directions, and their positions beforehand is of great help in crack sizing. Thus, not only the sensitivities but also the spatial resolutions are important. Numerical simulations are applied to help the design of the probe from the viewpoint of the crack sizing of steam generator tubes. Experiments show that the present probe provides both a high detectability and a remarkable capability of reconstructing the shallow cracks of a tube.

Identification of crack depths from eddy current testing signal

This paper demonstrates the identification of crack depths using signals obtained from eddy current testing (ECT). The identification method is based on finite elements with the pre-computed unflawed database approach and a meshless crack representation technique, and parameter estimation in nonlinear problems. Four different cracks are estimated by using laboratory data.

Identification of multiple cracks from eddy-current testing signals with noise sources by image processing and inverse analysis

This paper proposes a novel method for identifying the number and positions of cracks and reconstructing crack shapes. It assumes that two-dimensional scanned eddy-current testing (ECT) signals obtained from a steam generator tube are a picture image, then a template matching method with the help of genetic algorithms predicts the number and positions of cracks. The present method employs the superposition of crack signals and a nonlinear scaling technique of a signal profile on the crack length that are verified by numerical simulation. The number and positions of the cracks are satisfactorily predicted. The crack-shape reconstructions from the predicted positions with the help of inverse analysis are achieved with a satisfactory degree of accuracy.

Crack shape reconstruction in ferromagnetic materials using a novel fast numerical simulation method

This paper describes research on crack shape reconstruction in ferromagnetic materials using a novel fast numerical simulation method. The fast numerical method developed here, which can treat ferromagnetic materials, is an extension of a precomputed database approach based on the reduced magnetic vector potential method. It provides a fast forward simulator that is about 80 times faster than a conventional one, even in the case of ferromagnetic materials, without losing accuracy. The fast simulator is applied to the inverse problem of eddy current testing (ECT), crack shape reconstruction, and results of some electric discharge machining (EDM) cracks on a ferromagnetic plate are shown.

Fast Numerical Calculation for Crack Modeling in Eddy Current Testing of Ferromagnetic Materials

Eddy current testing (ECT) is a nondestructive testing method for metal materials. Numerical methods are applied to predict the ECT signals, to aid in the design of ECT probes, and to reconstruct crack shapes from their ECT signals. For the testing of nonferromagnetic materials, the high accuracy of some numerical simulation techniques has been demonstrated and several fast computational methods have been presented. However, the numerical calculation of electromagnetic fields in ferromagnetic materials remains a difficult and time-consuming task. Representing cracks in ferromagnetic materials with secondary electric and magnetic sources leads to a fast method for predicting ECT signals as presented in this article. The method developed here, that can be used to treat ferromagnetics, is an extension of the precomputed database approach based on the magnetic vector potential method. With the aid of precomputed databases, ECT signals of different cracks can be computed from changes in the secondary sources i...

Development of Eddy Current Probe for Thick‐Walled Plates and Quantitative Evaluation of Cracks

This paper demonstrates the crack detection of thick‐walled non‐magnetic metal plates by eddy current testing, which used to be difficult because of the skin effect generally. For the purpose, this paper proposes a novel eddy current testing probe for cracks in thick‐walled plates and evaluates the capability of the present probe. The probe was designed, based on the numerical computation using 3D fast eddy current code. The advantages of the present probe are strong eddy current on the back of specimens and small decay of eddy current in the thickness direction. Through experiments, we confirmed that this probe can detect the back artificial defect on INCONEL718 specimen with thickness of 7.0mm and 304 Stainless steel specimen with thickness of 8.0mm.

A novel crack reconstruction method for steam generator tube ECT with noise sources outside

In eddy current testing of steam generator tubes, the signals obtained are always noised by many factors because of the complex environment. Some of these noise factors are caused by the support plates, the expansion part of the tube and the tube sheets outside. Previous works show that the noises of support plates can be reduced by a multi-frequency method. However, the elimination of noises from the expansion part of the tube is proved impossible using the multi-frequency method only. A new signal processing method is introduced in this paper by applying a differential filter using the two dimensions scan data. Signal noise ratio (SNR) is increased significantly, even a small signal from outer defects can be recognized. Furthermore, a new method for the crack reconstruction from these noised signals has been developed with a fast signal prediction and the conjugate gradient algorithm considering the outside ferromagnetic structures such as support plates and tube sheets. The electromotive force signals ...