Ebook: Electromagnetic Nondestructive Evaluation (XII)

The 13th International Workshop on Electromagnetic Nondestructive Evaluation (ENDE) was held at the Seoul Education and Culture Center, Seoul, Korea from June 10 through 12, 2008. It was the first time that this workshop is held in Korea. The ENDE activities in Korea are largely focused on the safe operation of nuclear power plants, gas pipelines and petrochemical plants. To reflect concerns of Korean ENDE community, this workshop was held in conjunction with the 11th Workshop on Safety Diagnosis of Industrial Facilities to the Korean oil and gas industry and the 3rd Industry-University NDE Forum to the Korean nuclear industry.

The workshop was organized jointly by Sungkyunkwan University, Soongsil University and Kunsan National University, in cooperation with the Japan Society of Applied Electromagnetics and Mechanics (JSAEM), and with the contribution of the Korea Atomic Energy Research Institute (KAERI), the Korea Institute of Machinery and Materials (KIMM), the Korea Gas Safety Corporation (KGS), the Korea Electric Power Research Institute (KEPRI), Inha University, the Korea Research Institute of Standards and Science (KRISS), the Korea Institute of Nuclear Safety (KINS), the Korea Science Academy and the Research Institute of Industrial Science and Technology (RIST).

One hundred and sixteen participants were officially registered from Korea, Japan, China, the United States, France, Germany, Greece and Poland, and 75 papers were presented at the workshop. 51 reviewed and accordingly revised full papers have been accepted and are published in these edited proceedings.

Following welcoming remarks by Sung-Jin Song, the chairman, the technical program commenced with a keynote address, “Electromagnetic Nondestructive Evaluation in Korean Nuclear Power Plants” given by Dr. Myung-Ho Song, Director, Material Engineering department, Korea Institute of Nuclear Safety. The workshop talks were organized into eight sessions including one plenary talk, six oral sessions and one poster session. Topics of oral sessions were “ENDE in Nuclear Power Plant I (NPP)” chaired by Young-Kil Shin, “ENDE in Nuclear Power Plant II” chaired by Satish Udpa, “Corrosion under Insulation/Layer problem (CUI)” chaired by Theodoros Theodoilidis, on the first day, “Materials Characterization (MC)” chaired by Yong-Moo Cheong, “Inverse Problem & Imaging” chaired by Fumio Kojima, and “Modeling” chaired by Dominique Lesselier, on the second day. Three invited talks were given in NPP, CUI, and MC sessions. Professor Lalita Udpa gave an invited talk entitled “Meeting Steam Generator Tube Inspection Needs in Nuclear Power Plants”. Professor Norio Nakagawa presented the second invited talk, “Corrosion under Insulation: Electromagnetic NDE Capabilities” and Professor Tetsuya Uchimoto presented “Characterization of Matrices and Graphite Forms of Cast Irons by Electromagnetic Nondestructive Evaluation”. The poster session on the second day, chaired by Hyang-Beom Lee and Jin-yi Lee, allowed informal and informative discussions among participants with various backgrounds. The conference concluded with closing remarks by the chairman, Sung-Jin Song and the venue for the next workshop, which will be organized by Dr. Jeremy Knopp, was announced to be Dayton, Ohio, U.S.A.

The organizers would like to express their sincere gratitude to all the participants. The financial supports of the sponsors are also gratefully acknowledged. Thank are due to the members of the standing committee, particularly professors L. Udpa and T. Takagi, who provided considerable guidance and support. The editors are also indebted to the Korean ENDE community for their reviews of the papers. Lastly, we acknowledge the hard work of Sun-Feel Ko and Hye-Yoon Song for their invaluable help given to the editors during the preparation of workshop and this book.

Young-Kil Shin, Hyang-Beom Lee and Sung-Jin Song

Co-Editors

Since the application of electromagnetic induction or eddy current techniques to materials evaluation problems such as detecting surface or near surface cracks and measuring the thickness of thin plate and coatings was begun by many investigators in the late 1930s and early 1940s, commercial instruments based on this NDE method were used extensively during World War II. Eddy current transducers and electronic instrumentation have been greatly improved, and automated systems have been developed for material property determination and flaw detection applications. Nowadays eddy current techniques were applied to automobile, aerospace, metal-forming and nuclear industry etc. Especially fast inspection speed and automatic signal-collecting technique are available to implement the inspection of steam generator tube in nuclear power plant.

In this presentation, ECT techniques applied to Korean nuclear power plants and regulatory position for Korea NPP ECT inspection was discussed. For this, steam generator inspection in KNPPs was summarized and R&D techniques connected to ECT were introduced. Specially, ECT inspection technique for SG tube was explained from bobbin-probe to D-probe according to the development of technique. Also, the current regulatory status of steam generator ECT and ECT issues related to the integrity of steam generator tubes were summarized and future regulatory promise of steam generator ECT was suggested.

Accurate and consistent characterization of flawed regions in steam generator tubing is becoming increasingly important as nuclear power plants age and repair costs increase. The general problem of assessing the structural integrity of steam generator tubing using eddy current inspection techniques is rather complex due to the presence of noise and interfering signals under different inspection conditions. Additional difficulties in the data analysis task arise due to the fact that unwanted signals from support structures, probe wobble and geometry variations result are often similar to defect signals, thereby frustrating the characterization process. Automated analysis of eddy current inspection data can help in enhancing the accuracy and consistency of signal interpretation. This, in turn, offers significant benefits to utilities, including cost savings by reducing manpower needs, time savings by reducing the impact of analyst shortages during peak outage periods, providing analysis results at rates equal to or less than the rates for data acquisition, and reliability improvements by providing consistent, repeatable and accurate inspection results.

An overview of signal processing techniques for classification and characterization of defects in SG tubes along with typical implementation results will be presented. The automated signal analysis system provides utility engineers with detailed information on the dimension, shape, orientation, origin, and location of individual flaws within steam generator tubes. Such information can be employed by computational models for calculating burst and safe operating pressures.

Another tool that can help in improving inspection reliability is the availability of simulation models. The models enable visualization of field/flaw interaction, and better understand the effect of various geometrical and experimental parameters on flaw signals. A simple axisymmteric model for SG geometry with a user friendly interface can help in training operators. Such models can be employed to build probability of detection (POD) models capable of quantifying the capability of an inspection system.

Industrial systems such as chemical plants use extensive piping systems for transporting hazardous materials and pressure. Their integrity must be maintained stringently against degradations such as corrosion. According to Ref. [1], “chemical process system components are often made of carbon steel or steel alloys, and are covered with insulation.” Insulation may trap moisture underneath, causing “corrosion under insulation (CUI). This refers only to damage occurring between the inside layer of the insulation and the outside surface of the metal components.” Generally, piping may develop flaws such as cracks, pitting, local thin areas (LTAs), and blisters, among which CUI tend to form pits and LTAs on the outside surface [2]. Thus, characteristically, damages of CUI are local, the size ranging from much smaller than the pipe diameter to similar to the diameter.

It is also asserted [1] that “attempts to detect this corrosion have, in most cases, required the removal of insulation prior to inspection... It has been estimated that these efforts cost many hundreds of thousands of dollars.” There is thus a strong demand for appropriate NDE techniques for CUI without insulation removal/restoration. The challenge is significant because of the stand-off distance and the damage locality. Weatherproof coating over the insulation sometimes adds difficulty.

This presentation first reviews the lists of NDE methods applicable to CUI in the existing reports and papers [1-5], highlighting the three presently common implementations, i.e., real-time digital radiography, long-range (guided wave) ultrasonics, and pulsed eddy current (PEC). The second part of the paper is devoted to an examination of several electromagnetic methods, particularly PEC [4, 6], based on theoretical models and laboratory data. Novel modalities such as T-ray [7], with their plausibility, may be discussed.

Mechanical properties of cast irons are mainly determined by two factors of microstructures, graphite morphology and type of matrices. Both graphite morphology and matrices affect electromagnetic properties very complicatedly. The authors have investigated electromagnetic properties of flake graphite cast irons and ductile cast irons focusing on the their microstructures, and applied electromagnetic nondestructive evaluation method such as eddy current method, nonlinear eddy current method and DC potential drop method to characterize microstructures of various kind of cast irons. In this presentation, we review relationship between electromagnetic properties and microstructures. Issues discussed include graphite forms in fake graphite cast irons which is important to estimate damping and wear properties of flake graphite cast irons, ferrite and pearlite ratio in ductile cast irons which decides the hardness, and chill contents of both flake graphite cast irons and ductile cast irons. Finally, we discuss feasibilities of some applications of electromagnetic nondestructive evaluation methods to characterize graphite forms and matrices of cast irons.

In an attempt to attain “Zero Fuel Leaks by 2010”, EPRI is embarking on a multi-disciplinary approach to NDE of fuel rods. This involves fast screening technique based on guided wave to evaluate and discriminate presence of flaws from deposits and geometry variations on individual rods by allowing access to top ends of loaded fuel rods while they are still in the fuel bundle assembly. Once the degraded fuel rod is identified, it will be removed from the fuel bundle for further testing. One of the quantification NDE methods for flaw location, OD/ID flaw discrimination, and estimation of percent wall losses is eddy current.

This paper describes the current state-of-the-art eddy current array probe used to detect, discriminate, and size identified fuel rod degradations. Present emphasis is on testing removed dry fuel rods at a hot cell facility. To perform this evaluation, EPRI has assembled an eddy current hardware/software system that can drive a 32-element OD array probe in a transmit-receive mode to allow simultaneous detection of both OD and ID initiating axial, circumferential, and off-axis flaws. To evaluate the capabilities and limitations of the fabricated array probe, a number of machined and electro-discharge machined (EDM) notches were made out of Zircoloy 4 fuel rod materials. Current capabilities of the fabricated array probe to detect and characterize various flaw sizes of known orientations and flaw depths are presented.

In this paper we propose the nondestructive determination of the deuterium content from the pressure tubes using a classical eddy current multi frequency method. The conductivity of the zirconium alloy is determined by inversion, the influence of ZrO layer being eliminated. The developed model, the inversion method and the comparing of prediction - experiment are presented, the data obtained experimentally validating the proposed method.

We apply model-based inversion to problems of relevance to the nuclear power industry. We have acquired laboratory data for round-bottom, inner-diameter (ID) pit standards for heat-exchanger tubes from the Electric Power Research Institute (EPRI), and have then developed model-based standards for the inversion of these data using our proprietary volume-integral code, VIC-3D©. Results of the inversion process that show excellent agreement with the measured data will be presented.

GMR stands for giant magnetoresistance but the overall effective sensing size is around 1 mm in diameter. It represents the latest solid state thin-film magnetic sensor technology for detecting minute magnetic field perturbation, both DC and AC field, originating from materials under test. With wider frequency response of DC to megahertz range, it's ideally suited for nondestructive evaluation (NDE) applications involving detection of both DC field and AC field. To detect AC eddy current-to-flaw perturbation field, a separate excitation field is required to introduce eddy currents in a test sample.

EPRI has been evaluating the application of GMR-sensor based eddy current technology to power plant components made of stainless steel and Alloy 600 since 2005. The GMR-based eddy current instrument was successfully developed and fabricated along with several different probe types, which were tested on welded plate samples made of Inconel 182 materials. The fabricated GMR test instrument incorporated the use of unique probe design that would rely on the AC component of the sensor for flaw characterization and the DC component for material characterization.

This paper describes works on nondestructive evaluation of tube heat exchangers. A dedicated eddy current transducer was utilized. Various configurations were evaluated and the most promising one was selected. Additional signal processing algorithms were applied to extract useful information. The proposed solutions were tested using a real specimen with artificial defects.

A combined Finite Elements Method (FEM) – Volume Integral Method (VIM) approach is presented for the modeling of Steam Generator (SG) tube inspection in the vicinity of support plates. The coupled approach combines the flexibility of the FEM in modeling complex geometries with the numerical efficiency of the VIM, reducing the computational time demanded for the solution of the problem using the FEM only. Additional effects like material deposit between plate and tube can be also taken into account. The developed coupling technique is planed to be integrated in the CIVA nondestructive evaluation simulation platform.

The Korea Electric Power Research Institute established performance demonstration programs for non-destructive examination personnel who analyze eddy current data for steam generator tubing in the nuclear power plant. The purpose of these performance demonstration programs is to ensure a uniform knowledge and skill level of data analysts and contribute to safely operate the nuclear power plant. In Korea, there have been many changes in non-destructive examination of steam generator tubing such as inspection scope, plugging criteria and qualification requirements. According to the Notice 2008-23 revised by the Ministry of Education, Science and Technology, the analyst for steam generator tubing shall be qualified as the qualified data analyst, and the site specific performance demonstration program shall be implemented for them. KEPRI developed these performance demonstration programs and they are being successfully implemented. The analyst's performance is expected to be improved by the implementation of these programs.

A magnetic phase is partly produced in steam generator tube by stress and heat, because the steam generator tubes are used under high temperature, high pressure and radioactivity. It causes trouble for the safety of the steam generator tubes, but it is difficult to detect it by conventional eddy current methods. So a new type of probe is needed to distinguish between the signals from the defects and the magnetic phases. We designed a new U-type yoke which has two kinds of coils, one a magnetizing coil, and the other a detecting coil, and we simulated the signal induced by the ferromagnetic phase and the defect existed in the Inconel 600 plate.

The effects of the ECT (Eddy Current Test) Signal influenced by TSP (Tube Support Plate) blockage by sludge pile at nuclear power plant SG (Steam Generator) are studied in this paper. Model 51B SG has quatrefoil type flow holes in TSP and has a tendency to clogging up the flow holes at the flow-stagnated region with the sludge. The sludge pile deposited on the TSP flow holes makes the flow be blocked, and causes the steam generator water level oscillation. Therefore, it is necessary to know how much portion of the TSP holes is obstructed by the sludge pile for the safe operation. Some methods are used to measure the extent; visual test (VT), wide range water level monitoring, and ECT. The method introduced in this paper is based on the ECT. The TSP blockage is simulated in a mock-up with the artificially fabricated sludge pile. The relationship between the extent of blockage and the ECT signal acquired by the bobbin and MRPC (Motorized Rotating Pancake Coil) is studied. A quantitative result for the blockage is obtained. A conversion table is developed from the MRPC probe test, which helps to estimate the blockage level from the bobbin probe signal. Applying the technique introduced in this paper to S/G tube inspection with other method complementarily, it is expected to improve the accuracy of estimating the flow hole blockage level and to give a guidance to SG management program.

This work mainly deals with the characterization of the delaminations in the fibre-metal laminates as the Glare®. We present a direct model based on Electromagnetic Coupled Circuit Method (ECCM). This model has been improved and coupled with analytical computations to avoid the discretization of the load. The number of unknowns needed for obtaining the sensor impedance variations is reduced and computation of the direct model has been sped up. Thus, an optimization algorithm could be applied to obtain the material physical properties and the delamination geometrical parameters in multilayer materials. The particle swarm optimization (PSO), a recent powerful optimization technique, is then coupled with the direct model in an inversion process, providing the desired parameters. Some examples, linked to aeronautics, are presented: thickness of layers and delamination geometrical characterization in fiber-metal laminate material as Glare®. Experimental results are shown and analyzed in comparison.

This paper deals with the estimation of conductivity profiles using Eddy-Current measurements over combustion turbine blade coatings affected by depletion of aluminium. First, we model the response of an Eddy-Current coil over a layered metallic structure with a top over-aluminized coating by extending the analytical Uzal-Rose's model for one hyperbolic tangent conductivity profile to a conductivity profile using two hyperbolic tangents for taking inward and outward depletion of aluminum inside the coating into account. Results obtained with this model are similar to those obtained with a numerical multi-layer model with a reduced computing time.

We report on a self-calibrated, swept frequency eddy current (SFEC) technique for characterization of surface conditions of materials such as residual stresses or service-induced degradation. We started with the lift-off normalized V-component signal technique, which was introduced to suppress the lift off noise and instrumentation effect. The technique was expanded to a wider frequency range by using multiple coils. Our theoretical study shows that the V-component signals are insensitive to coil dimensions, thus enabling multiple coil measurements in separate frequency bands, while yielding a continuous broad-band data. We demonstrate the technique on two surface-modified materials, namely Inconel 718 samples shot peened at 4A to 8A, and an Ag-1.5at%Al alloy subjected to surface oxidation. For each sample, the V-component signals measured using two dissimilar sets of coils and instruments were found to overlap, confirming that the signals are insensitive to coil dimensions and instrumentation. The bulk conductivities of the samples were determined by inverting the low frequency data. The bulk conductivities were then used to constrain model-based inversion of the high frequency data to obtain conductivity profiles from which the residual stress profile of the shot-peened Inconel 718 and the oxidization depth of the Ag-Al alloy can be inferred.

A scanning probe microscope (SPM) technique has been used to investigate the material properties of self-assembled monolayers (SAMs) on gold. We demonstrate that SPM can achieve contactless detection of the thickness of SAMs. By measuring the reflection coefficient S₁₁ at an operating frequency near 5.3 GHz, we could observe the thickness of SAMs. This nano-scale measurement of SAMs has a great potential for investigating the surface profile with high sensitivity.

This paper describes the development of a high resolution eddy current imaging system by combining the basic principles of conventional eddy current and an atomic force microscope (AFM). The eddy currents are generated by exciting a small coil, placed under an electrically conductive sample, with a low frequency electromagnetic signal. The eddy currents through the sample are detected by a magnetic film coated AFM tip-cantilever. The force between the coil and the magnetic tip, with and without the electrically conductive sample, is related to the electrical conductivity, at that location in the sample. The images of the electrical conductivity variations in the sample are obtained by scanning the sample with a magnetic film coated tip. Eddy current images of metal, composite, and nano-composites are presented. A theoretical model developed to evaluate the response of the magnetic film coated AFM tip under the eddy current excitation is described. The results obtained on simple metals are compared with the theoretical model. The model is used to interpret in general the observed contrast and features in different materials.

In pulsed eddy current testing (ECT), much information can be obtained by a measurement. Understanding the electromagnetic phenomena in pulsed ECT is necessary for establishment of the design method of probe and the processing method of detected signal. In this paper, a simple axisymmetric aluminum plate model was investigated by using finite element analysis. We tried to clarify the electromagnetic phenomena in the aluminum plate model excited by pulsed source current and collect fundamental data for the investigation of three-dimensional problems.

Trends in the automotive industry tend towards fuel saving and reduction of exhaust gases by weight reduction. On the other hand the enhancement of safety is required. From this it follows an increased application of high strength steels as well as stainless steels in the car body production. The forming of these materials is associated with high requirements to forming procedure and forming tools. In comparison with forming of low strength steels the risk of spring back effects is increased caused by higher amount of elastic deformation. Furthermore during deep drawing processes tearing nearby the die corner may occur because load strengths in this area are too large. These load strengths are so called “plane strain” states.

In order to avoid or reduce failure a monitoring of the stress states during the deep drawing process should be implemented. Basically the non-destructive electromagnetic testing method 3MA (Micromagnetic Multiparameter Microstructure and Stress Analysis) is convenient to characterize stress states. A special miniaturized electromagnetic probe, a so called rotating field probe, which is able to detect multiaxial stress states, was developed.

In a first step measurements in a cross tensile test, which allows the generation of the critical “plane strain” state, were performed. Systematic dependencies between the electromagnetic signals and the strain states could be observed. Based on these measuring results the rotating field probe was integrated in a deep drawing tool. During the deep drawing process changes in the strain states could be detected nondestructively for the first time.