Detection of the Subsurface Cracks in a Stainless Steel Plate Using Pulsed Eddy Current
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Detection of the Subsurface Cracks in a Stainless Steel Plate Using Pulsed Eddy Current Duck-Gun Park · C. Sekar Angani · B.P.C. Rao · Gabor Vértesy · Duk-Hyun Lee · Kyung-Ho Kim
Received: 16 February 2013 / Accepted: 20 June 2013 © Springer Science+Business Media New York 2013
Abstract The nondestructive method to detect subsurface defects is limited because conventional eddy current are concentrated near to the surfaces adjacent to the excitation coil. The PEC technique enables detection of cracks buried deeper under the surface with relatively small current density. In the present study, an attempt has been made to investigate detection of subsurface cracks using a specially designed double-D differential probe. The tested sample is a SS304 with a thickness of 5 mm; small EDM notches were machined in the test sample at different depths from the surface to simulate the sub surface cracks in a pipe. The designed PEC probe has two excitation coils and two detecting Hall-sensors. The difference between two sensors is the resultant PEC signal. The cracks under the surface were detected using peak amplitude of the detected pulse; in addition, for a clear understanding of the crack depth, the Fourier transform is applied. In time domain, the peak amplitude of the detected pulse is decreased, and in the frequency domain, the magnitude of the lower frequency component has been increased with an increase in the crack depth. The experimental results have indicated that the proposed differential probe has the potential to detect the sub surface cracks in a stainless steel structure. D.-G. Park (B) · D.-H. Lee · K.-H. Kim Nuclear Materials Development Division, Korea Atomic Energy Research Institute, 305-353 Yuseong, Taejon, South Korea e-mail: [email protected] C.S. Angani · B.P.C. Rao Nondestructive Evaluation Division, IGCAR, Kalpakkam, Tamil Nadu, India G. Vértesy Research Center for Natural Sciences, Institute of Technical Physics and Materials Science, Konkoly Thege Miklós út 29–33, 1121 Budapest, Hungary
Keywords Sub-surface cracks · Pulsed eddy current · Peak amplitude · Fourier transform
1 Introduction Nondestructive testing (NDT) of the steel structures for the identification of sub-surface cracks has always been of great industrial interest. The flaws are a real threat for the reliability of a structure, as they can rapidly grow to cause failures of the structural integrity. To prevent these failures NDT is used as a predictive approach to maintain the safety of the structures [1]. PEC testing has been demonstrated to be one of the most effective methods, which is capable of tackling different inspection tasks, such as sub-surface defect detection in complex structures [2–4]. Among the available conventional NDT methods, eddy current testing (ECT) is the most promising technique to detect flaws in conductive materials [5, 6]. The conventional ECT uses single frequency sinusoidal excitation for the detection of defects or flaws as a function of change in voltage, impedance or phase, because of limited depths o
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