Influences of Excitation Current Frequency and Amplitude on Corrosion Evaluation Based on Analytical Model for Surface M
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LECTROMAGNETIC METHODS
Influences of Excitation Current Frequency and Amplitude on Corrosion Evaluation Based on Analytical Model for Surface Magnetic Field Feng Jianga, b, Shulin Liub, *, and Shaojie Xinc aSchool
of Electrical and Information Engineering, Changzhou Institute of Technology, Changzhou, 213032 China of Mechatronics Engineering and Automation, Shanghai University, Shanghai, 200072 China cSchool of Mechanical Engineering, Shanghai DianJi University, Shanghai, 201306 China *e-mail: [email protected]
bSchool
Received October 27, 2018; revised July 27, 2019; accepted August 30, 2019
Abstract—The influences of excitation current on the evaluation of the corrosion with a cylindrical shape in a semi-infinite plate are presented in this paper. First, axi-symmetric model of the cylindrical coil above the corroded plate is established and an analytical solution to the surface magnetic field is derived by means of the truncated region eigenfunction expansion method (TREE). Then, the effect of the excitation current frequency and amplitude on the surface magnetic field is investigated and quantitatively evaluated. It is found that the radial magnetic induction intensity increases as the excitation current frequency increases, whereas the axial magnetic induction intensity decreases. The excitation current amplitude is proportional to the radial and axial magnetic induction intensities and does not affect the phase of magnetic induction intensity. As a result, the influence node for detecting the radius and the hollow depth for detecting the hidden depth are obviously dependent on the excitation current frequency in terms of the butterfly-shaped graph. The calculation results are in good agreement with the numerical simulation, showing that the developed model can be used to predict the optimal excitation current frequency. This work indicates that an appropriate excitation current frequency, such as f = 500 Hz, can improve the characteristic parameter resolution for detecting the corrosion radius. For the detection of hidden depth, the lower excitation current frequency, such as f = 100 Hz, can amplify the defect phenomenon and improve the detection accuracy. It is not only helpful to develop the analytical model for the surface magnetic field, but also to optimise the parameters of the test device. Keywords: excitation current, surface magnetic field, analytical model, corrosion evaluation DOI: 10.1134/S1061830920080057
INTRODUCTION The eddy current testing based on the principle of electromagnetic induction is one of the five conventional nondestructive testing techniques. It has the advantages of high speed, low cost and noncontact. It is widely used in the quality and structural integrity testing and evaluation of metals and alloys [1–3]. The theoretical models can be used in understanding the physical mechanism, optimising the design of the probe and the detection parameter, and even calculating and evaluating defects detection probability [4, 5]. Compared with numerical models, analytical models provide
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