Magnetic charge model of defect in magnetic flux leakage testing

2020 ◽  
Vol 64 (1-4) ◽  
pp. 1315-1323
Author(s):  
Ranran Huang ◽  
Hongmei Li ◽  
Mingyang Jiang ◽  
Yu Wang ◽  
Chuntian Zhao
Keyword(s):  
Magnetic Flux ◽  
Structural Integrity ◽  
Magnetic Charge ◽  
Magnetic Flux Leakage ◽  
Structural Safety ◽  
Magnetization Distribution ◽  
Near Surface ◽  
Charge Model ◽  
Flux Leakage ◽  
Magnetic Flux Leakage Testing

The defect in structures is the major risk to the structural integrity, thus to perform the defect detections and evaluations efficiently is critical in assuring the structural safety. Magnetic flux leakage testing (MFLT) is an important non-destructive testing (NDT) method. Due to its high testing sensitivity and simple operating procedure, it has been widely used in detecting surface and near-surface defects in ferromagnetic components. To improve the accuracy of defect detection, it is necessary to find a suitable source magnetization distribution around a defect, and furthermore, to correlate the defect with the magnetic leakage signals. In this study, a magnetic charge model is proposed, in which both volume- and surface- densities of magnetic charges around a defect are considered. Then, this model is used for the calculation of the magnetic leakage signals caused by a known complex V-shape defect for the verification purpose. The results from the simulation match very well with that from the experiment. It indicates potentials that the magnetic charge model and the associated approach can be applied in MFLT with improved accuracy.

Solenoid Model for the Magnetic Flux Leakage Testing Based on the Molecular Current

2018 ◽  
Vol 54 (12) ◽  
pp. 1-14
Author(s):  
Yonggang Wang ◽  
Yuhua Cheng ◽  
Libing Bai ◽  
Jie Zhang ◽  
Haichao Yu ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Magnetic Flux Leakage ◽  
Flux Leakage ◽  
Magnetic Flux Leakage Testing

Practical evaluation of velocity effects on the magnetic flux leakage technique for storage tank inspection

2020 ◽  
Vol 62 (2) ◽  
pp. 73-80
Author(s):  
A L Pullen ◽  
P C Charlton ◽  
N R Pearson ◽  
N J Whitehead
Keyword(s):  
Magnetic Flux ◽  
Storage Tank ◽  
Eddy Currents ◽  
Surface Defects ◽  
Signal Amplitude ◽  
Magnetic Flux Leakage ◽  
Scanning Velocity ◽  
Near Surface ◽  
Practical Evaluation ◽  
Flux Leakage

Magnetic flux leakage (MFL) is a technique commonly used to inspect storage tank floors. This paper describes a practical evaluation of the effect of scanning velocity on defect detection in mild steel plates with thicknesses of 6 mm, 12 mm and 16 mm using a fixed permanent magnetic yoke. Each plate includes four semi-spherical defects ranging from 20% to 80% through-wall thickness. It was found that scanning velocity has a direct effect on defect characterisation due to the distorted magnetic field resulting from induced eddy currents that affect the MFL signal amplitude. This occurs when the inspection velocity is increased and a reduction in the MFL signal amplitudes is observed for far-surface defects. The opposite applies for the top surface, where an increase is seen for near-surface MFL amplitudes when there is insufficient flux saturating the inspection material due to the concentration of induced flux near the top surface. These findings suggest that procedures should be altered to minimise these effects based on inspection requirements. For thicker plates and when far-surface defects are of interest, inspection speeds should be reduced. If only near-surface defects are being considered then increased speeds can be used, provided that the sensor range is sufficient to cope with the increased signal amplitudes so that signal clipping does not become an issue.

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