Ebook: Electromagnetic Nondestructive Evaluation (X)

The 11th International Workshop on Electromagnetic Nondestructive Evaluation (ENDE) was held at the Hotel APPI Grand in Hachimantai-shi, Iwate, Japan, on June 14th–16th, 2006. The workshop was organized by NDE & Science Research Center, Faculty of Engineering, Iwate University, and financially supported and co-sponsored by Japan Society of Maintenology, the Iron and Steel Institute of Japan and the Japanese Society for Non-Destructive Inspection, and sponsored by the Japan Society of Applied Electromagnetics and Mechanics, the Institute of Electrical Engineers of Japan and the Magnetic Society of Japan.

Following welcoming remarks by Prof. Seiki Takahashi, workshop chair, there were 46 presentations given at the workshop: 3 invited talks, 29 oral and 14 poster presentations. Three invited talks were given by Dr. Masaaki Kurokawa, Mitsubishi Heavy Industries Ltd., Prof. Anthony Moses, Cardiff University, and Dr. Gábor Vértesy, Hungarian Academy of Sciences.

The workshop was organized into 9 oral sessions and 1 poster session: “ECT modeling” chaired by D. Lesselier, A. Tamburrino, “ECT Modeling and Simulation” chaired by G. Rubinacci, T. Takagi, “Eddy Current Testing” chaired by J. Pàvò, T. Theodoulidis, “New Methods” chaired by K. Ara, S. Udpa, “Industrial Applications”, Y. Tsuchida, T. Uchimoto, “NDE by Magnetism I” chaired by D.G. Park, G.Y. Tian, “NDE by Magnetism II” chaired by P. Novotný, S. Takahashi, “Inverse Problem” chaired by Z. Chen, L. Janousek, “Inverse Problem and Benchmark” chaired by G. Berthiau, F. Kojima. The workshop was concluded with closing remarks by Prof. Fumio Kojima.

The main theme of the ENDE workshop has been on “Eddy Current Testing” to identify cracks in metals and alloys. Since the first ENDE workshop was held in London 1995, the seeing of workshops have contributed the technical advance in ECT through our competition and collaboration. ECT is put to practical use in industry now as one of the approved methods of crack detection in steels and metallic structures.

We added the new topics in APPI meeting, i.e. magnetic NDE method according to the concept of NDE & Science Research Center. Two of three invited talks are on the magnetic NDE.

Forty-eight participants were registered for this workshop from different parts all over the world; France, Italy, Hungary, China, Korea, UK, USA, Czech Republic, Germany, Greece, Poland, Slovakia and Japan. Short versions of all contributed papers have been published in the workshop abstracts, and 33 full papers were accepted after review and are published in “Electromagnetic Nondestructive Evaluation (X)” published by IOS Press in the series “Studies in Applied Electromagnetic and Mechanics.”

We could concentrate our interest on the academic exchange and the sincere discussion for three days, since APPI is located in an out-of-the way place. All the participants enjoyed the beautiful green, fresh air, good taste water and the lovely concert.

The workshop organizers gratefully acknowledge the financial support of the sponsors and would like to thank the session chairs and the participants. Thanks are also due to the members of the standing committee. The editors are truly thankful to referees listed below, especially regional editors, Professors G. Rubinacci, T. Takagi and S.S. Udpa.

The next ENDE meeting will be held from June 19th to 21st 2007 in Cardiff under the auspices of Wolfson Center for Magnetics Technology, Cardiff School of Engineering, Cardiff University.

Seiki Takahashi, Iwate University, Morioka, Iwate, Japan, Workshop Chair and Co-Editor

Hiroaki Kikuchi, Iwate University, Morioka, Iwate, Japan, Co-Editor

A semi-analytical forward model based on the electromagnetic coupled circuits method is presented. This model allows to simulate the impedance variation of a ferrite-cored sensor above a controlled material. The computational speed is increased by determining the current density in coil using the Kelvin analytical distribution. This forward model provides a good accuracy with respect to experimental measurements.

In the framework of a collaborative project with EADS, a semi-analytical model based on a volume integral method has been developed to simulate eddy current (EC) inspection of riveted structures in aeronautics. The model handles a layered structure by considering a dyadic Green's approach where a fastener and a flaw are introduced as a variation of conductivity in a stack of slabs. Experimental data are used to validate the model.

This work focuses on an innovative Eddy Current Imager dedicated to the high-speed and high-resolution non-destructive testing of large metallic structures, such as the riveted lap joints of aircrafts. The system produces time-harmonic in – phase and in – quadrature eddy current images, thanks to a specific linear magneto-optic set-up, which actually provides a true measurement of the 2-D spatial distribution of the magnetic flux density at the surface of the inspected structure. In view of quantitative imaging of defects in planar structures, an appropriate numerical model, based on an efficient integral formulation, is presented and validated against the measurements.

Recently we presented an analytical solution for the 3D configuration of a cylindrical coil at the edge of a conductive block and calculated the impedance variation with position relative to the edge. Since then we have been seeking ways to improve and extend the analytical and numerical treatment of this canonical problem. In the present paper, several extensions to previous work are presented including a modification to the expressions for the field potentials in double series form and the generalization of the field source to coils of arbitrary shape and orientation. Experimental results involving a cylindrical coil of arbitrary tilt are shown to verify the calculations.

This paper is concerned with the dyadic Green formalism in order to develop simulation tools dedicated to Eddy Current Non Destructive Testing (ECNDT). The Volume Integral Method (VIM) is useful when considering volumetric flaws. The Surface Integral Method (SIM) is more appropriate for thin opening flaws. This latter fast method provides accurate results, except in some critical Transmitting / Receiving (T/R) configurations. In such cases, we propose to combine VIM and SIM to obtain satisfactory results.

An axisymmetric cup-cored coil placed above a layered conductive halfspace is analyzed by using the truncated region eigenfunction expansion method. Closed-form expressions are presented for the coil impedance as well as the induced eddy current density. The results are in very good agreement with results from 2D-FEM and with experimental ones.

This paper presents a contribution in the framework of a novel method to extract defect location in conductive materials using data obtained from diffusive nondestructive evaluation (NDE) techniques such as eddy current testing. The method is based on the definition and extraction of the Time of Flight (TOF) for diffusive phenomena by using the Q-transform, a mapping that associates a wave propagation problem to a diffusion problem. In this work we present the method for extracting the TOF from diffusive data together with experimental and numerical tests for a simple configuration. The results clearly demonstrate the application of Q-Transform based approach in a realistic NDE setting.

This work focuses on a eddy current system based on a new inversion principle requiring the processing of low frequency measurements of the matrix of self and mutual impedances among coils of an array of coils. Numerical simulations presented in another work have proven that this algorithm is suitable for fast inversion of ECT data. This work is focused on a first experimental prototype tailored for the particular inversion algorithm. Specifically, we show that measurements of the impedance matrix can distinguish between volumetric defects of different lengths and we discuss the main issues to be solved in view of the inversion of the experimental data.

The paper proposes a novel method for crack evaluation based on electromagnetic induction phenomenon. The principle of the method is to realize a unique distribution of induced eddy currents by superposition of several phase-shifted exciting electromagnetic fields. The ratio of the superposition is varied to inspect a crack using different distributions of eddy currents without changing the frequency. Numerical and experimental results reveal that the method provides clear indication about the depth of cracks. In addition, the method is applicable even for cracks which are much deeper than the standard depth of penetration.

This paper presents a methodology using Eddy Current Testing (ECT) for the discrimination of two types of cracks commonly found in Japanese nuclear power plants: Stress Corrosion Cracks (SCCs) and Fatigue Cracks (FCs). The discrimination is based on the extraction of relevant features that are classified using two classifiers. These classifiers are trained with simulated features and tested with experimental ones. More meaningful results with regard to the discrimination problem are obtained through the introduction of a so-called cautious classifier.

Type IV damage in power plants is a premature failure that occurs in the softened heat-affected zone (HAZ) of weldment. Eddy-current method is applied to evaluate electromagnetic properties of high-chromium ferritic steels in order to investigate the material changes of HAZ and base metal in Type IV damage evaluation. A pancake-coil impedance model based upon eddy current theory is proposed to evaluate conductivity and permeability. A series of HAZ and base metal specimens of Modified 9Cr-1Mo steel in different heat treatment conditions are experimentally measured and then their conductivity and permeability are estimated. The evaluated results illustrate electromagnetic properties between heat treatment specimens in different test time can be clearly distinguished by presented approach.

The purpose of this paper is to present the results of observation of fatigue failures forming under cyclic dynamic loading using selected electromagnetic NDT methods. To evaluate fatigue damage a multi-frequency eddy current and induced current field measurements methods were used.

Crack detection is one of the most important issues in large component such as nuclear power plant. A NDT method using electromagnetic waves has strong possibility for crack detection in large pipes. In this study, TM01-mode of electromagnetic wave is used for detecting a circumferential crack and time of flight (TOF) of the electromagnetic wave in straight pipe with crack is evaluated to determine the crack location.

Microwave nondestructive evaluation techniques proposed for civil structures and cement based materials offer distinct advantages in that they are non-radioactive and provide good penetration, excellent contrast between steel reinforcement material and concrete, and insensitivity to ambient temperature. This paper presents a far field frequency domain reflection coefficient measurement setup for non-invasive inspection of cement-based materials at microwave frequencies. Imaging results obtained in the X-band frequency for planar mortar and concrete samples in the presence of steel reinforcement bar are discussed.

Steam generator tubes in nuclear power plants are continuously exposed to harsh environmental conditions including high temperatures, pressures, fluid flow rates and material interactions resulting in various types of degradation mechanisms. Consequently they need to be inspected periodically for cracks and leaks. Multi-frequency eddy current technique is one of the widely used Non-Destructive Evaluation (NDE) techniques for steam generator tube inspection in nuclear power industry. The multi-frequency technique enables nullifying the effect of extraneous discontinuities via multi-frequency mixing and improves defect identification, classification and characterization of the eddy current data. In this paper, different defect characterization algorithms developed for the multi-frequency eddy current data obtained from the heat exchange tubes is discussed. A comprehensive comparison of the performance of the different characterization algorithms is also presented.

An application of electromagnetic nondestructive evaluation is presented in the paper: Laser scribed markers used as logistic codes on metallic components are reconstructed from the signal of an eddy current probe. The authors developed a computational model of the reading out process by which both the code specification and the probe can be optimized. The model is applied here for the optimization of marker density. The reconstruction of barcode using inverse filtering approach is also demonstrated.

The paper deals with the design of a special remote field eddy current probe dedicated for inspections of a magnetic tube from its outer surface. A simple configuration of the probe with one exciting coil and one pick-up coil is considered. The coils are shielded with magnetic material to gain the remote field effect in the given configuration. Results of numerical investigations prove the effectiveness of the probe.