A Novel Magnetic Flux Leakage Testing Method Based on AC and DC Composite Magnetization
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A Novel Magnetic Flux Leakage Testing Method Based on AC and DC Composite Magnetization Rongbiao Wang1 · Yihua Kang1 · Jian Tang1 · Bo Feng1 · Yongle Deng1 Received: 27 June 2020 / Accepted: 31 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The flexible printed coil array (FPC) is employed extensively because of its flexibility in non-destructive testing (NDT). To make the inductive coil detect both external and internal defects under static conditions in magnetic flux leakage testing (MFL), this paper proposes a method based on the AC and DC composite magnetization. The AC magnetization changes the magnetic field strength in the vicinity of external defects. The DC magnetization makes the defects generate static leakage magnetic field. The permeability in the skin layer is also altered by the AC magnetization which affects the transmission of leakage magnetic field caused by internal defects. Therefore, external and internal defects can generate a time-varying leakage magnetic field. Simulations and experiments are carried out to validate the feasibility of this method. The results indicate that the method based on the AC and DC composite magnetization can be applied to detect both external and internal defects. Keywords Composite magnetization · Magnetic shielding · MFL · Internal defects · Permeability
1 Introduction The flexible sensor array is widely applied in non-destructive testing (NDT) [1], such as the flexible ultrasonic array probe [2–4] in ultrasonic testing (UT) and the flexible printed coil array (FPC) probe [5–8] based on printed circuit board (PCB) in eddy current testing (ECT). With the FPC, a certain area can be detected without scanning. Besides, the specimen with complex contours such as the pipe bend and the welded seam can be inspected because the shape of FPC can be changed to suit the contour. Because of its advantage, it is gradually used in the direct current magnetic flux leakage (DC-MFL) testing [9] which is applied widely in the detection of ferromagnetic materials. However, the FPC can only measure the change of the magnetic field rather than the absolute value of the leakage magnetic field [10]. Therefore, the FPC can be applied at high speed. While under the condition that the high detection speed cannot be realized, such as the detection of pipe bends and in-service inspection, the FPC is unable to detect the static leakage magnetic field.
B 1
Yihua Kang [email protected] State Key Lab of Digital Manufacturing Equipment & Technology, Huazhong University of Science and Technology, Wuhan, China
In order to detect the defect with coils statically, the alternating current magnetic flux leakage (AC-MFL) technique can be adopted, which generates a time-varying magnetic field [11, 12]. However, due to the skin effect, only surface or near-surface defects can be detected [13]. To improve the penetration depth of AC-MFL, Tsukada et al. [14] used the excitation current with extremely low frequencies. The backside pitting of a 10 mm thickne
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