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The magnetic flux leakage (MFL) method has very good defect detection and location capabilities, but defect sizing capabilities, especially for sub-surface defect characterisation, are limited. The pulsed magnetic flux leakage (PMFL) technique has recently been introduced and shown to have great potential for automated defect sizing for surface-breaking defects using time-frequency signal processing techniques, but sizing of sub-surface defects has proved problematic. In this paper, pulsed magnetic reluctance (PMR), a new electromagnetic (EM) non-destructive evaluation (NDE) technique, is introduced and incorporated into a dual PMFL/PMR probe for the characterisation of surface and sub-surface defects in ferromagnetic materials. Experimental results from a comparison study of the two techniques using variety of defects analysed using time-frequency analysis show that the techniques offer complementary information, with PMFL providing defect location data and data for the characterisation of surface defects and PMR offering sub-surface defect characterisation capabilities. The work concludes that integration of these inspection techniques in the new pulsed EM probe can provide enhanced defect characterisation capabilities for flux leakage-based inspection systems using relatively simple time-frequency signal processing techniques. 相似文献
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Experiment and simulation study of 3D magnetic field sensing for magnetic flux leakage defect characterisation 总被引:1,自引:0,他引:1
Magnetic flux leakage (MFL) testing is widely used to detect and characterise defects in pipelines, rail tracks and other structures. The measurement of the two field components perpendicular to the test surface and parallel to the applied field in MFL systems is well established. However, it is rarely effective when the shapes of the specimens and defects with respect to the applied field are arbitrary. In order to overcome the pitfalls of traditional MFL measurement, measurement of the three-dimensional (3D) magnetic field is proposed. The study is undertaken using extensive finite element analysis (FEA) focussing on the 3D distribution of magnetic fields for defect characterisation and employing a high sensitivity 3-axis magnetic field sensor in experimental study. Several MFL tests were undertaken on steel samples, including a section of rail track. The experimental and FEA test results show that data from not only the x- and z-axes but also y-axis can give comprehensive positional information about defects in terms of shape and orientation, being especially advantageous where the defect is aligned close to parallel to the applied field. The work concludes that 3D magnetic field sensing could be used to improve the defect characterisation capabilities of existing MFL systems, especially where defects have irregular geometries. 相似文献
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The investigation described in this paper focuses on the velocity effect of dynamic magnetization and magnetic hysteresis due to rapid relative motion between magnetizer and measured specimens in high-speed magnetic flux leakage (MFL) inspection. Magnetization intensity and permeability of ferromagnetic materials along with the duration of dynamic magnetization process were analyzed. Alteration of the intensity and distribution of magnetic field leakage caused by permeability of specimen were investigated via theoretical analysis and finite-element method (FEM) combined with the actual high-speed MFL test. Following this, a specially designed experimental platform, in which motion velocity is within the range of 5 m/s–55 m/s, was employed to verify the velocity effect and probability of a high-speed MFL test. Preliminary results indicate that the MFL technique can achieve effective defect inspection at high speeds with the maximum inspection speed of about 200 km/h being verified under laboratory conditions. 相似文献
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由于高速漏磁检测下速度效应的存在,检测信号会发生畸变。根据漏磁检测中速度效应的基本原理可知,速度感应产生的涡流是直接影响漏磁检测信号的因素之一,而且其大小同速度及磁场强度成正比。因此文章根据高速检测的这一特点,建立了新的高速检测模型,对一系列运行在不同速度下有缺陷的钢轨模型进行了有限元仿真,并将该模型下的检测信号与经典漏磁模型的检测信号对比,进一步认识了涡流效应对检测信号的影响。 相似文献
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Metal loss defects in a buried pipeline are detected by magnetic flux leakage technique. Characterisation of the defects and sentencing according to the severity is extremely important for organised maintenance of pipelines. In this paper we identify the parameters that characterise a defect and the features of magnetic flux leakage signal (MFL) that are affected by those parameters. We show that analysis of the MFL signal using wavelet transform scores over any other method of its kind and exposes the incompleteness of the other analysis techniques that have appeared in the literature, to date. A number of experiments were performed on a rotating drum test rig having defects of different shapes and sizes. The results from these experiments are presented and discussed in detail. Wavelet transform decomposition and reconstruction techniques were applied for denoising the raw data. We test the efficacy of discrete wavelet transform for denoising MFL signal and present a complete scheme of characterisation of defects from denoised MFL signal. We discuss the issue of defect classification and suggest that characterisation to specified accuracy, amounts to designing a classifier that assigns a defect into known classes whose shapes and sizes are defined a priory. 相似文献
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Keiji Tsukada Mitsuteru Yoshioka Toshihiko Kiwa Yoshinobu Hirano 《NDT & E International》2011,44(1):101-105
Spot welding is widely used for joining metal plates. However, a highly reliable monitoring method is needed to weld a robust structure. For this purpose, we developed a magnetic flux leakage (MFL) system using a magnetoresistive (MR) sensor for nondestructive spot-weld inspection. The magnetic flux is induced between two joined plates, and the magnetic flux leakage with a tangential component parallel to the plate surface is measured. A magnetic image at the spot-welding part is obtained by two-dimensional scanning. The connected diameter of the nugget and the maximum shear load are measured after the magnetic measurement to investigate their interrelationship. The results show that the nondestructive magnetic flux leakage test shows a good correlation with the destructive shear test. 相似文献
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3D FEM analysis in magnetic flux leakage method 总被引:6,自引:0,他引:6
The magnetic flux leakage (MFL) method is currently the most commonly used pipeline inspection technique. In this paper, 3D FEM is used to analyze the MFL signals, a generalized potential formulation to the magnetostatic field MFL problem is discussed, typical 3D defects are accurately modeled and detail MFL signal in test surface are calculated by the method. The relation between defect parameters and MFL signals are also analyzed. 相似文献
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Pipelines are an important transportation medium for petroleum and chemical products, but defects in the pipelines can present hidden dangers and affect the safe operation of the pipeline. The traditional pipeline magnetic flux leakage (MFL) scanning technique generally adopts the axial magnetization mode, which has increased the difficulty in detection and the possibility of missed detection of axial cracks. In this paper, a new composite MFL method using alternating magnetic field excitation is proposed for the detection of cracks in pipelines. The alternating magnetic field is first superimposed on the MFL magnetization field, which will form a parallel eddy current field perpendicular to the magnetization direction in the pipeline wall. The defects in the pipeline not only cause the flux leakage of the magnetization field, but also lead to the disturbance of the circumferential eddy current field. The disturbance signals can be picked up through a secondary induced magnetic field. Because the magnetic field and the eddy current field are orthogonal, the presented method can implement synchronous detection in two orthogonal directions to avoid missed detection caused by the crack orientation. A series of physical experiments are carried out in this paper. The results show that two orthogonal detection signals can be separated by a simple low pass filter. Therefore, with only one scan, the new detector can obtain the defect characteristics in the axial and circumferential directions to overcome the blind spot problem seen in traditional MFL detectors. 相似文献
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Defects due to corrosion can occur on top and bottom surfaces of a tank floor. The current magnetic flux leakage (MFL) tank inspection machines can detect and locate defects on both the top and bottom of a plate, but generally they are unable to differentiate between top and bottom. Further cleaning for visual inspections is needed to identify those defect that are on the top side and are thus more readily repaired. To avoid this additional inspection ideally the machine should be able to distinguish automatically between top and bottom surface corrosion. This paper presents experimental work specifically designed to asses the capability of current MFL based machines to distinguish defects located on the top and those on the bottom of the tank floor. Although some open literature suggests that such top or bottom classification might be possible, purpose designed experimental results presented here show that there is a very high similarity between signals belonging to top and bottom defects which suggests such discrimination is not viable using standard MFL based techniques. 相似文献
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L. Clapham T. W. Krause H. Olsen B. Ma D. L. Atherton P. Clark T. M. Holden 《NDT & E International》1995,28(2)
Gas pipelines are inspected for defects such as corrosion. The most commonly used nondestructive inspection tool uses the magnetic flux leakage (MFL) technique. The MFL signals depend on the magnetic behaviour of the pipe, which is sensitive to its microstructure and crystallographic texture as well as both residual and applied stresses. Here a section of commercial X70 pipeline is characterized using microstructural examination, X-ray diffraction (to determine crystallographic texture) and neutron diffraction (for residual stress measurement). The results correlate well with the manufacturing steps used for this type of pipe. Magnetic characterization is also performed using magnetic Barkhausen noise measurements, which reflect the magnetic anisotropy in the pipe and thus the MFL signal. These results do not correlate simply with crystallographic texture and residual strain results, but this is not unexpected given the complex nature of the material and its stress state. 相似文献
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Magnetic flux leakage (MFL) obtained during the inspection of oil and gas pipelines has been simulated using 3D finite element analysis. The interaction between nearby corrosion pits has been studied. It is found that the alignment of the pits has significant effects on the absolute values of MFL signals due to its affect on the magnetic flux density distribution. 相似文献