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http://dx.doi.org/10.4283/JKMS.2011.21.1.023

A Study on the Method of Magnetic Flux Leakage NDTfor Detecting Axial Cracks  

Yun, Seung-Ho (Dept. of Electrical Engineering, Pusan National University)
Park, Gwan-Soo (Dept. of Electrical Engineering, Pusan National University)
Publication Information
Journal of the Korean Magnetics Society / v.21, no.1, 2011 , pp. 23-31 More about this Journal
Abstract
From among the NDT (nondestructive testing) methods, the MFL (magnetic flux leakage) method is specially suitable for testing pipelines because pipeline has high magnetic permeability. The system applied to MFL method is called the MFL PIG. The previous MFL PIG showed high performance in detecting the metal loss and corrosions. However, MFL PIG is highly unlikely to detect the cracks which occur by exterior-interior pressure difference in pipelines and the shape of crack is long and very narrow. In MFL PIG, the magnetic field is performed axially and there is no changes of cross-sectional area at cracks that the magnetic field passes through. Cracks occur frequently in the pipelines and the risk of the accident from the cracks is higher than that from the metal loss and corrosions. Therefore, the new PIG is needed to be researched and developed for detecting the cracks. The circumferential MFL (CMFL) PIG performs magnetic fields circumferentially and can maximize the magnetic flux leakage at the cracks. In this paper, CMFL PIG is designed and the distribution of the magnetic fields is analyzed by using 3 dimensional nonlinear finite element method (FEM). In CMFL PIG, cracks, standards of NACE, are detectable. To estimate the shape of crack, the leakage of magnetic fields for many kinds of cracks is analyzed and the method is developed by signal processing.
Keywords
MFL; NDT (nondestructive testing); axial cracks; in-line inspection; CMFL; FEM;
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