• Title, Summary, Keyword: Magnetic Flux Leakage (MFL)

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A Study on Determining the Shape of Small Axial Cracks by using Magnetic Flux Leakage in NDT System for Underground Pipe (배관용 자기누설 비파괴 검사에서 축방향 미소결함의 형상 판정에 관한 연구)

  • Kim, Hui Min;Park, Gwan Soo
    • Journal of the Korean Magnetics Society
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    • v.23 no.1
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    • pp.18-25
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    • 2013
  • MFL PIG (Magnetic Flux Leakage Pipeline Inspection Gauge) is called the system which detects the defect for underground pipelines by using magnetic flux leakage method in nondestructive testing. This method is very suitable for testing pipelines because pipeline has high magnetic permeability. MFL PIG generates the magnetic fields to the pipe axially oriented, and detect the signal of leakage flux by using hall sensor. However, MFL PIG is hard to detect the axially oriented crack with small size because the magnetic flux leakage is not enough to be occurred. To detect the small size and axially oriented crack, the circumferential MFL (CMFL) PIG is being proposed and it can maximize the leakage flux for the axial crack by performing magnetic fields circumferentially on the pipe. In this paper, CMFL PIG is applied to detect the axially oriented crack with small size and the analysis for the distribution and the amplitude of the leakage flux signal is performed by using three dimensional finite element method. From sensing signals, the method how to determine the shape of axially oriented cracks is proposed and verified with experiment.

Improvement of MFL sensing-based damage detection and quantification for steel bar NDE

  • Kim, Ju-Won;Park, Minsu;Kim, Junkyeong;Park, Seunghee
    • Smart Structures and Systems
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    • v.22 no.2
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    • pp.239-247
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    • 2018
  • A magnetic flux leakage (MFL) method was applied to detect and quantify defects in a steel bar. A multi-channel MFL sensor head was fabricated using Hall sensors and magnetization yokes with permanent magnets. The MFL sensor head scanned a damaged specimen with five levels of defects to measure the magnetic flux density. A series of signal processing procedures, including an enveloping process based on the Hilbert transform, was performed to clarify the flux leakage signal. The objective damage detection of the enveloped signals was then analyzed by comparing them to a threshold value. To quantitatively analyze the MFL signal according to the damage level, five kinds of damage indices based on the relationship between the enveloped MFL signal and the threshold value were applied. Using the proposed damage indices and the general damage index for the MFL method, the detected MFL signals were quantified and analyzed relative to the magnitude of the damage increase.

Effect of Double Circular Pit Depth and Stress on Far and Near-side Magnetic Flux Leakage at Ferromagnetic Pipeline (강자성 배관 외.내부 면의 이중 원형 결함의 깊이와 응력이 누설자속에 미치는 영향)

  • Ryu, K.S.;Park, Y.T.;Son, D.;Atherton, D.L.;Clapham, L.
    • Journal of the Korean Magnetics Society
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    • v.13 no.2
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    • pp.76-81
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    • 2003
  • Non-linear anisotropic materials were used to simulate the effects of tensile stress in 3D finite element analysis (FEA). FEA was used to calculate the effects of far and near-side pit depth and tensile stress on magnetic flux leakage (MFL) signals. The axial and radial MFL signals were depended on far and near-side double circular pit depth and on the stress, but the circumferential MFL signal was not depended on them. The axial and radial MFL signals increased with greater pit depth and applied stress, but the circumferential MFL signal was scarcely changed.

Corrosion Assessment of In-pipe using Magnetic Flux Leakage Technique (누설자속법을 이용한 배관내부 부식 평가)

  • 이원용;이병주;양성일;김영주;안봉영
    • 제어로봇시스템학회:학술대회논문집
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    • pp.402-402
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    • 2000
  • MFL(Magnetic Flux Leakage) methods are used extensively for inspection of ferromagnetic materials. As an example, pipelines that are buried underground are inspected using MFL methods. By the MFL methods, ferromagnetic pipelines are magnetized by a permanent magnet or an electromagnet and then flux leakage is detected at the defection position. In this paper, we perform modeling of the magnetized pipelines. Also we propose the method localization of th defected areas. The effectiveness of the proposed method is verified experimentally.

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Implementation of a Modified SQI for the Preprocessing of Magnetic Flux Leakage Signal

  • Oh, Bok-Jin;Choi, Doo-Hyun
    • Journal of Magnetics
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    • v.18 no.3
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    • pp.357-360
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    • 2013
  • A modified SQI method using magnetic leakage flux (MFL) signal for underground gas pipelines' defect detection and characterization is presented in this paper. Raw signals gathered using MFL signals include many unexpected noises and high frequency signals, uneven background signals, signals caused by real defects, etc. The MFL signals of defect free pipelines primarily consist of two kinds of signals, uneven low frequency signals and uncertain high frequency noises. Leakage flux signals caused by defects are added to the case of pipelines having defects. Even though the SQI (Self Quotient Image) is a useful tool to gradually remove the varying backgrounds as well as to characterize the defects, it uses the division and floating point operations. A modified SQI having low computational complexity without time-consuming division operations is presented in this paper. By using defects carved in real pipelines in the pipeline simulation facility (PSF) and real MFL data, the performance of the proposed method is compared with that of the original SQI.

Development of Intelligent Pig for Detecting Corrosion on Pipeline Using MFL Technology (MFL 기술을 이용한 천연가스 배관 부식 검사용 인텔리전트 피그 개발)

  • Cho, S.H.;Kim, Y.K.;Park, D.J.;Yoo, H.R.;Koo, S.J.;Park, S.S.;Kim, D.K.;Rho, Y.W.
    • Proceedings of the KSME Conference
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    • pp.235-240
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    • 2001
  • This paper introduces developed prototype intelligent pig which detects corrosion on pipeline by using Magnetic Flux Leakage technology. The 8 inch developed MFL(Magnetic Flux Leakage) pig is composed of 5 yokes which magnetize pipeline wall and 45 Hall sensors which detect MFL signal. The designed MFL modules are analyzed by using magnetic circuit method in order to confirm whether pipeline wall is fully saturated. A variety of artificial defects are manufactured on 8 inch diameter steel pipeline in order to acquire MFL signals. So leakage flux of the axial, radial and circumferential component was acquired as defects. The results of this paper show that design technique for 8 inch MFL pig can be applied to large diameter MFL pig and 0.5mm defect depth can be detected.

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Effect of Ear and Near-side Single Circular Pit Depth and Bulk Stress on Magnetic Flux Leakage at ferromagnetic Pipeline (강자성 배관 외.내부 면의 단일 원형 홈의 깊이와 부피응력이 누설자속에 미치는 영향)

  • Ryu, Kwon-Sang;Park, Young-Tae;Atherton, D.L.;Clapham, L.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.23 no.3
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    • pp.263-269
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    • 2003
  • Magnetic flux leakage (MFL) signals were used for corrosion inspection of buried oil and gas pipeline. 3D finite element analysis was used to examine the effects of far and near-side pit depth and tensile stress on MFL signals. Anisotropci materials were used, and the effects of simulated tensile stress on MFL were investigated. The axial and radial MFL signals depended on far and near-side single pit depth and on the bulk stress, but the circumferential MFL signal did not depend on them. The axial and radial MFL signals increased with increasing pit depth and the bulk stress, but the circumferential MFL signal was scarcely changed.

Study for Development of Nondestructive Inspection Device in Natural Gas Pipeline Using MFL Technology (MFL을 이용한 천연가스 배관용 비파괴 검사장비 개발에 관한 연구)

  • Cho S.H.;Kim D.K.;Park D.J.;Park S.S.;Yoo H.R.;Koo S.J.;Rho Y.W.;Kho Y.T.
    • Journal of the Korean Institute of Gas
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    • v.6 no.1
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    • pp.10-16
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    • 2002
  • This paper introduces developed prototype intelligent pig which detects corrosion on pipeline by using Magnetic Flux Leakage technology. The 8 inch developed MFL(Magnetic Flux Leakage) pig is composed of 5 yokes which magnetize pipeline wall and 45 Hall sensors which detect MFL signal. The designed MFL modules are analyzed by using magnetic circuit method in order to confirm whether pipeline wall is fully saturated. A variety of artificial defects are manufactured on 8 inch diameter steel pipeline in order to acquire MFL signals. So leakage flux of the axial, radial and circumferential component was acquired as defects. The results of this paper show that design technique for 8 inch MFL pig can be applied to large diameter MFL pig and 0.5mm defect depth can be detected.

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Characteristics Magnetic Flux Leakage According to the Position of Hall Sensor (Hall 센서 위치에 따른 MFL 특성 고찰)

  • Kim, Sean;Lee, Hyang-Beom
    • Proceedings of the KIEE Conference
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    • pp.819-821
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    • 2001
  • This paper describes a characteristics of MFL according to the position of Hall sensor Magnetic Flux Leakage(MFL) Method is used to detect surface defect in ferromagnetic plate. A plate has a surface defect and magnetizing equipment are producted to perform Non-Destructive Testing(NDT) using MFL. The SM 45C carbon steel plate is adopted to this experiment. there is a artifical defect with a twice of thickness and a half of depth of plate. Magnetizing equipment is composed of yoke made by layer-built of silicon sheet steel, NdFeB magnetic and iron brushes. Detecting defect is performed by MFL NDT using Hall sensor. It is shown that magnetic flux detected by Hall sensor is affected according to the position of Hall sensor through MFL experiment and numerical analysis.

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Optimum Design of a Non-Destructive Testing System to Maximize Magnetic Flux Leakage

  • Park, G.S;Jang, P.W;Rho, Y.W
    • Journal of Magnetics
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    • v.6 no.1
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    • pp.31-35
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    • 2001
  • This paper describes the design method of a magnetic system to maximize the magnetic flux leakage (MFL) in a non-destructive testing (NDT) system. The defect signals in a MFL type NDT system mainly depend on the change of the magnetic leakage flux in the region of a defect. The characteristics of the B-H curves are analysed and a design method to define the operating point on B-H curves for maximum leakage is performed. The computed MFL signal by a nonlinear finite element method is verified by measurement using Hall sensors mounted on the 6 legs PIG, the traveling detector unit in gas pipe, in an 8 inch test tube with defects. The rhombic defects could be successfully identified from the defect signals.

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