eddy current imager based on bobbin-type hall ...

REVIEW OF PROGRESS IN

QUANTITATIVE NONDESTRUCTIVE EVALUATION Denver, Colorado, USA 15 – 20 July 2012

VOLUME 32A EDITORS Donald O. Thompson Dale E. Chimenti Iowa State University, Ames, IA

SPONSORING ORGANIZATIONS QNDE Programs Air Force Research Laboratory Army Research Laboratory American Society of Nondestructive Testing (ASNT) AMES Laboratory of the Department of Energy Federal Aviation Administration (FAA) National Aeronautics and Space Administration (NASA) National Science Foundation (NSF) Industry/University Cooperative Research Centers

CD INCLUDED IN VOLUME 32B

Melville, New York, 2013 AIP CONFERENCE PROCEEDINGS

1511

REVIEW OF PROGRESS IN

QUANTITATIVE NONDESTRUCTIVE EVALUATION Denver, Colorado, USA 15 – 20 July 2012

VOLUME 32B EDITORS Donald O. Thompson Dale E. Chimenti Iowa State University, Ames, IA

SPONSORING ORGANIZATIONS QNDE Programs Air Force Research Laboratory Army Research Laboratory American Society of Nondestructive Testing (ASNT) AMES Laboratory of the Department of Energy Federal Aviation Administration (FAA) National Aeronautics and Space Administration (NASA) National Science Foundation (NSF) Industry/University Cooperative Research Centers

CD INCLUDED

Melville, New York, 2013 AIP CONFERENCE PROCEEDINGS

1511

Table of Contents

페이지 5 / 19

Y. T. Tsai, M. R. Haberman, and J. Zhu

CHAPTER 2 ELECTROMAGNETICS, THERMOGRAPHICS, AND THERMOSONICS Section A. Eddy Current - Mostly Modeling Eddy current mapping inside a plane conductor with flaws A. Lopes Ribeiro, H. Geirinhas Ramos, D. J. Pasadas, and T. J. Rocha Modeling and simulation of crack detection for underwater structures using an ACFM method Wei Li, Guoming Chen, Xiaokang Yin, Chuanrong Zhang, and Tao Liu BEM modeling for ECT simulation of complex narrow cracks in multilayered structures R. Miorelli, C. Reboud, T. Theodoulidis, and D. Lesselier Investigation of acoustic fields generated by eddy currents using an atomic force microscope V. Nalladega, S. Sathish, and M. Blodgett Role of varying interface conditions on the eddy current response from cracks in multilayer structures Aaron Cherry, Jeremy Knopp, John C. Aldrin, Harold A. Sabbagh, Thomas Boehnlein, and Ryan Mooers

Section B. Eddy Current - Techniques and Probes Eddy current NDE performance demonstrations using simulation tools L. Maurice, V. Costan, E. Guillot, and P. Thomas Saturated low frequency eddy current technique applied to phases characterization in duplex stainless steel J. M. A. Rebello, C. G. Camerni, M. C. Areiza, R. O. Carneval, and R. W. F. Santos Low frequency EC-GMR detection of cracks at ferromagnetic fastener sites in thick layered structure G. Yang, A. Tamburrino, Z. Zeng, Y. Deng, X, Liu, L. Udpa, and S. S. Udpa Development of flexible array eddy current probes for complex geometries and inspection of magnetic parts using magnetic sensors B. Marchand, J.-M. Decitre, N. Sergeeva-Chollet, and A. Skarlatos Finite element modeling of magnetic bias eddy current probe interaction with ferromagnetic materials J. Lei Eddy current imager based on bobbin-type Hall sensor arrays for nondestructive evaluation in small-bore piping system Jongwoo Jun, Jinyi Lee, Jungmin Kim, Minhhuy Le, and Sehoon Lee

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2013-03-11

EDDY CURRENT IMAGER BASED ON BOBBIN-TYPE HALL SENSOR ARRAYS FOR NONDESTRUCTIVE EVALUATION IN SMALL-BORE PIPING SYSTEM Jongwoo Jun1, Jinyi Lee1,2,*, Jungmin Kim2, Minhhuy Le2,and Sehoon Lee3 1

Research Center for Real Time NDT, Chosun University, Gwangju, 501-759, Korea 2 Department of Control and Instrumentation, Chosun University, Gwangju, 501-759, Korea 3 Nedtech Co. Ltd., Busan, 617-050, Korea ABSTRACT. A bobbin coil with bobbin-type solid-state Hall sensor arrays was proposed for eddy current testing. A 32×32 matrix of InSb Hall sensors was set on a cylinder 15 mm in diameter and 25 mm long. The distorted alternating magnetic fields around inner diameter (ID) and outer-diameter stress corrosion cracks (ODSCCs)were imaged at 1 fps. The effectiveness of the proposed techniquewas verified with a standard copper alloy specimen with hole-type circumferential ID- and ODSCCs. Keywords: Eddy Current, Image, Sensor Array, Non-Destructive Testing, Pipeline, Hall Sensor PACS: 85.75.Nn, 85.80.Jm, 85.70.Ay

INTRODUCTION Advanced nondestructive testing (NDT) methodologies that enable specimens to be inspected for small cracks without cleaning are in great demand. In addition, the capacity for quantitative nondestructive evaluation (QNDE) and the construction of a database are crucial. In accord with the above-mentioned capabilities, NDT methodologies have been developed with a focus on the following trends: combining several NDT techniques; improvement of sensitivity and resolution by using semi-conductor and electric engineering; high-speed (i.e., real-time) inspection, automation of inspection process, visualization of inspection results, and database construction. Magnetic cameras have been developed according to above-mentioned capabilities and trends. A magnetic camera consists of a magnetic source, an object (i.e., a metallic specimen), magnetic sensor arrays, signal processing circuits, and computer, as shown in Fig. 1. An external magnetic or electrical field is applied to the object. The presence of defects distorts the distribution of the magnetic field around the object. The distorted magnetic field can be measured by using magnetic sensor arrays and signalprocessing-circuits. The measured magnetic field can be digitized, stored, calculated, analyzed, and displayed by using analog-to-digital converters (ADCs) and a computer. The 39th Annual Review of Progress in Quantitative Nondestructive Evaluation AIP Conf. Proc. 1511, 502-509 (2013); doi: 10.1063/1.4789089 © 2013 American Institute of Physics 978-0-7354-1129-6/$30.00

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FIGURE 1.

Composition of magnetic camera.

Magnetic cameras are classified by the sensor arrays and magnetic sources used. As shown in Fig. 2, magnetic cameras based on magnetic vector fields as well as linearly (LIHaS) [1-3], area-type (AIHaS) [4-6], and cylinder-type integrated Hall sensor arrays (CIHaS) [7] have been developed. Single- and differential-type Hall sensors with a spatial resolution of 0.52–0.78 mm are arrayed along a linear or curved line in the LIHaS, as shown in Fig. 2 (a). In the AIHaS, Hall sensors are arrayed on a NiZn ferrite wafer as a matrix (e.g., 32×32, 48×53) with a spatial resolution of 0.78 mm, as shown in Fig. 2 (b). In the CIHaS, Hall sensors are arrayed as a 32×32 matrix on a cylinder with a diameter of 15 mm, as shown in Fig. 2 (c). There are no limits to the number of sensors. There are two types of magnetic source: static and dynamic. When a magnetic field from a static-type magnetic source is applied to a specimen, the magnetic flux leaks around a crack, as shown in Fig. 3(b). This leakage can be measured by using the abovementioned sensor arrays. Therefore, a magnetic camera that uses a static-type magnetic source is useful for magnetic flux leakage testing (MFLT). On the other hand, current is induced when an alternating current is applied to a specimen by using a dynamic-type magnetic source, as shown in Fig. 3(b). The induced current is distorted around a crack. The magnetic field due to the eddy current around a crack can be measured by using a LIHaS, AIHaS, and CIHaS. Therefore, a combination of dynamic-type magnetic source and magnetic sensor arrays isuseful for eddy current testing (ECT).

(a) LIHaS FIGURE 2.

(b) AIHaS

Classification by sensor arrays.

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(c) CIHaS

(a) Static-type FIGURE 3.

(b) Dynamic-type

Classification by magnetic source.

Here we propose a magnetic camera that can be used to inspect the inner-diameter (ID) and outer-diameter (OD) stress corrosion cracks (SCCs) in a small-bore piping system such as a steam generator or condenser by using a CIHaS and a dynamic-type magnetic source. Furthermore, a standard copper alloy specimen with hole-type and circumferential ID- and ODSCCs was used to verify the effectiveness of the proposed technique. PRINCIPLES Figure 4 shows a bobbin-type Hall sensor array. InSb Hall sensors were arrayed in a 32×32 matrix on a wafer, which was bent to have a diameter of at least 15 mm, as shown in Fig. 4(a). The sensors were then fixed onto a non-metallic fixture (Fig. 4(b)), and electric wires connected by using wire ball bonder (Fig. 4(c)). Subsequently, the sensors with connecting wires were molded by using anti-shock insulation resin (Fig. 4(d)). A coil was wound around the molded sensor arrays to induce current in the pipeline (Fig. 4 (e)). Figure 5 shows a block diagram of the proposed bobbin-type magnetic camera. The 32×32 Hall sensors are operated by using 32 power lines and 32 signal lines. When one of the power lines is turned on, one of the sensor arrays along the row direction is in the active state. Column-direction signal lines are connected with amplifiers (AMPs), high-pass-filters (HPFs), root-mean-square circuits (RMSs), and ADCs with paralleltypeconnections. Therefore, the RMS signals from 32 Hall sensors along a row-direction can be digitized at the same time. RMS signals from entire matrix-type sensor arrays can be measured by switching on the power lines in order.

(a) Arraying and bending

(b) Fixing

(c) Connecting

(d) Molding FIGURE 4.

(e) Coiling Hall sensor arrays with cylinder-type fixture.

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FIGURE 5.

Block diagram.

On the other hand, an alternating electric field is induced in a piping system by supplying an alternating current to a coil. The induced current is then distorted by the presence of ID- and ODSCCs. The distributions of the magnetic field and RMS signals change owing to the distorted current (i.e., eddy current). Two modes are proposed in this paper to inspect ID- and ODSCCs: the scanning mode and the real-time imaging mode. In the scanning mode, 32 sensors along the row direction are selected to measure the distribution of the magnetic field. Sensor arrays with an inducing coil move in the axial direction in a small-bore piping system. Continuous eddy current images are obtained in the scanning mode. The area-type distribution of the magnetic field due to the eddy current can then be measured and displayed by using sensor arrays arranged in a 32×32 matrix in a certain area where a crack is detected. As mentioned above, the number of sensors is not limited to 32×32. EXPERIMENT AND DISCUSSION We used Hall sensors arranged into a magnetic sensor array (32×32) with a spatial resolution of 0.78 mm. The diameter and length of the bobbin-type sensor arrays were 15 mm and 25 mm, respectively. Given the number of sensors and the diameter of the bobbin, the measurement area has an angle of 202° and a length of 25 mm. The diameter and number of turns for the bobbin coil were 0.25 mm and 120 turns, respectively. An alternating current of 450 mA and 5 kHz was supplied to the bobbin coil. The speed of power switching in the real-time imaging mode was 30 ms. Hence, the frame speed was 1 fps. Hole- and circumferential-type ID- and ODSCCs of different sizes were introduced in a standard specimen (ASME/ID PIT CAL. STD for YG12) made from copper alloy (Cu 90%, Ni 10%; Table 1). The ID, thickness, and length of the specimen were 16.56 mm (0.65 in), 1.27 mm (0.05 in) and 500 mm (1.97 in), respectively. In Table 1, H and C represent hole-type and circumferential-type, respectively; ID and OD represent

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TABLE 1.

Shape and size of ID- and ODSCCs in a small-bore piping system with copper alloy.

No.

shape

1 2 3 4 5 6

H-ID H-ID H-ID H-T H-OD H-OD

Depth [mm] 0.30 0.60 0.90 1.01 0.65

Width [mm] 3.0 3.0 3.0 3.0 3.0 3.0

Volume [mm3] 2.12 4.24 6.36 9.60 7.14 4.60

No.

shape

7 8 9 10 11 12

H-T H-ST H-OD H-OD C-OD C-ID

Depth [mm] 0.81 0.38 0.22 0.22

Width [mm] 1.0 2.0/1.0 2.5 4.5 3.0 1.0

Volume [mm3] 1.07 2.76 3.98 6.04 17.72 4.58

ID- and ODSCCs, respectively; and T and ST represent through-hole and stepped throughhole, respectively. Figure 6 shows the experimental setup. A CIHaS and bobbin coil are fixed on a jig and inserted in a small-bore piping system. A specimen is fixed on the scanning system and moved in the axial direction, and the CIHaS is operated by electrical circuits (Fig. 5). Figure 7 shows experimental results in the scanning mode and real-time imaging mode, which are denoted as linear scan and area scan, respectively. Each image is the processed result of using Equation (1). 

(1)

Here, VRMS(i, j) expresses the RMS signal at a certain point (i, j). The axial and angular directions are indicated as i and j, respectively. Therefore, VRMS(i, j) expresses the difference of VRMS(i, j) from the neighboring sensor or position in the axial direction. In the scanning mode, the continuous RMS images (i.e., eddy current images) are clearer than the images in the real-time imaging mode. In addition, ODSCCs as well as IDSCCs were detected. As shown in box No. 10, 3 ODSCCs were detected. Although there are 4 ODSCCs, only 3 cracks were detected because the measuring region was 202°. Furthermore, circumferential ODSCCs and IDSCCs were detected, as shown in boxes No. 11 and No. 12, respectively. Here, we note that when a circumferential crack is oriented along the same direction as that of the current induced by the bobbin coil, the detectability of cracks is minimized. Nonetheless, the circumferential IDSCC and ODSCC could be detected and displayed.

FIGURE 6.

Experimental setup.

506

FIGURE 7.

Experimental results.

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Figure 8 expresses the relationship between the integral of VRMS(i, j) and the crack volume. The integral of VRMS(i, j) is expressed by following Equation (2).



(2)

In this figure, m and n represent certain areas of the RMS distribution (15 and 11, respectively, are used in this paper), and IDSCC and ODSCC are represented by large and small symbols, respectively. In addition, open and filled symbols represent VRMS in the scanning mode and real-time imaging mode, respectively. As shown in the figure, VRMS is larger in the scanning mode than in the real-time imaging mode. Moreover, the VRMS of IDSCCs is larger than that of ODSCCs. The figure shows a linear relationship between the VRMS and the crack volume. However, the data for boxes No. 11 and No. 12, which represent circumferential cracks, lie outside of the linear relationship because the crack shape is different and the eddy current is minimized owing to the direction of the induced current. Finally, the data point for box No.10 also resides outside of the linear relationship. This is because the depth of an ODSCC is small compared with its width; hence, the crack volume deviates from that of other cracks (e.g., No. 5).

FIGURE 8.

Relationship between integral of VRMS(i, j) and crack volume.

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SUMMARY A bobbin coil combined with bobbin-type solid-state Hall sensor arrays was proposed as an alternative NDT technology. The sensor array allows the imaging of the eddy current around ID- and ODSCCs of a small-bore piping system without the need for any rotating apparatus. A 32×32 matrix of InSb Hall sensors with a spatial resolution of 0.78 mm was set on a cylinder with a diameter of 15 mm and a length of 25 mm. The distorted alternating magnetic fields around ID- and ODSCCs were imaged at a speed of 1 fps. The induction frequency of the bobbin coil was 5 kHz. A standard specimen made of copper alloy with hole-type and circumferential IDand ODSCCs was used to verify the effectiveness of the proposed technology. Hole-type SCCs with a width ranging from 1 to 4.6 and a depth ranging from 18 to 100% were detected. The electro-magnetic field on circumferential ID- and ODSCCs oriented in the same direction as the current induced by the bobbin coil were imaged. The volume of each SCC was estimated by using the absolute integral of the magnetic image. ACKNOWLEDGMENTS This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2011-0030110). Also parts of research were supported by the MKE(The Ministry of Knowledge Economy), Korea, under the ITRC(Information Technology Research Center) support program(NIPA-2012H0301-12-2008) supervised by the NIPA(National IT Industry Promotion Agency). REFERENCES 1. J. Jun, M. Choi, and J. Lee, IEEE Trans. Magn. 47(10), 3959-3962 (2011). 2. J. Jun, M. Choi, J. Lee, J. Seo, and K. Shin, NDT E Int. 44, 449-455 (2011). 3. J. Lee, J. Hwang, J. Jun, and S. Choi, J. Mech. Sci. Technol.22, 2310-2317 (2008). 4. J. Lee, M. Choi, J. Jun, S. Kwon, J.-H Kim, J. Kim, and M. Le, IEEE Trans. Instrum. Meas., DOI: 10.1109/TIM.2012.2199190 (2012). 5. J. Jun, Y. Park, and J. Lee, Journal of Electrical Engineering 61(7), 32-35 (2010). 6. J. Hwang, J. Kim, and J. Lee, “Magnetic Images of Surface Crack on Heated Specimen using an Area-Type Magnetic Camera with High Spatial Resolution”, in I2MTC 2009 IEEE International Instrumentation and Measurement Technology Conference Proceedings, edited by M. H. Er, V. Piuri, S. Demidenko, R. Ottoboni, Institute of Electrical and Electronics Engineers, Piscataway, NJ, 2009, pp.1546-1551. 7. J. Lee, J. Jun, J. Kim, H. Choi, and M. Le, IEEE Trans. Magn. 48(11), MAGCON-1203-0188(2012).

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