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High-speed non-destructive inspection (NDI) systems using magnetic flux leakage method (MFL) is in great demand in online metal inspection and defect characterisation, especially in pipeline and rail track inspection. For MFL systems at high speed measurement, in addition to magnetic flux, eddy currents exist in metal specimen because of the relative movement between the probe and specimen. These currents alter the profile of electromagnetic field, which increases difficulty in signal interpretation and defect characterization. In this paper, eddy currents generated by high speed movement and their characterisation in high-speed MFL inspection systems were investigated by using numerical simulations. Besides, the MFL signals from high speed MFL measurement against defect depth were examined. 相似文献
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S. Saha S. Mukhopadhyay U. Mahapatra S. Bhattacharya G.P. Srivastava 《NDT & E International》2010,43(6):507-512
Magnetic flux leakage (MFL) technique is one of the oldest and most commonly used technique for detecting corrosion in the pipe wall as well as pipeline features like welds, valves, supports, attachments, etc. The MFL data obtained is processed for detecting (isolating) defect or feature signal and characterizing it for the purpose of sizing or assigning a template. This paper discusses the methodology adopted for analysis of radial MFL signal. The characterization of the defects is based on primary and secondary parameters of the radial MFL signature. Primary parameters are axial and circumferential spread and amplitude of the signature. In addition, secondary parameters like shape and extent of the signature are also considered. Accuracy and confidence of sizing achieved by the proposed scheme are validated by several dig site inspections of actual buried oil pipelines. 相似文献
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Natural gas is normally transported through a vast network of pipelines. A major segment of this network employs seamless pipes. The manufacturing processes associated with the production of seamless pipes contribute to a helical variation in the grain properties of the pipe. This introduces an artifact, known as the seamless pipe noise (SPN), in the data obtained from magnetic flux leakage (MFL) inspection of these pipelines. SPN can overwhelm the signals generated by defects and other elements in pipelines, and can therefore, mask their indications in the MFL data. This paper presents a new technique for detecting signals in MFL data obtained from seamless pipes. The overall approach employs an adaptive filter and a wavelet based de-noising technique. The algorithm is computationally efficient and data independent. Results from application of the approach to data from field tests are presented. 相似文献
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漏磁检测技术广泛应用于储罐底板扫查、管道内壁缺陷检测中。文章以裂纹漏磁场为研究对象,以麦克斯韦方程组为理论基础,以数值模拟为手段,建立裂纹漏磁场三维静态数值模拟模型,用数值模拟和试验方法研究裂纹深度、宽度、裂纹倾斜角度以及裂纹间距等参数对裂纹漏磁场的影响,得到裂纹参数与裂纹漏磁场幅值之间的关系。结果表明:裂纹倾斜角度对裂纹漏磁场幅值影响显著,因此在工程实际检测中,要从不同方向进行漏磁扫描,以防止漏检;当两条裂纹间距〈5mm时,裂纹漏磁场将产生叠加。数值模拟结果与试验数据较为一致,表明所用数值方法的有效性。文章所得结论对裂纹漏磁检测工程实践有重要的拳者意义。 相似文献
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Magnetic flux leakage (MFL) is the most used technique for pipeline inspection, being applied through the use of instrumented PIGs. The pipe wall is magnetized and when metal loss or other irregularities occur, a larger fraction of the magnetic flux “leaks” outwards from the wall and is detected by sensors. MFL presents some limitations since it requires magnetic saturation of the pipe wall. Therefore, it is difficult to inspect small diameter and thick wall pipelines. Internal corrosion sensor (ICS) has been developed as a solution for internal corrosion measurements of thick walls. The technique, also called “field disturbance”, is based in a direct magnetic response from a small area of the wall. It is not necessary to achieve the magnetic saturation of the pipe material, and thus ICS performance is not affected by the thickness of the pipe wall. In the present work, finite element calculations are performed and the best resultant configuration of the sensor is proposed. Experimental tests with a prototype were carried out and the results give a strong indication of the validity of the theoretical model proposed for sizing. 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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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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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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Correlation canceling principle used in pipeline head inspection 总被引:1,自引:1,他引:0
Magnetic flux leakage (MFL) is—concerning the detection of surface-near and surface-braking defects—the most commonly used method in inspecting steel pipelines after production and in service. In this paper, we attempt to use a new method based on MFL to inspect pipeline heads. We introduce the idea of a generalized characterization of the leading pipeline (in the joining region) in order to define a reference signal of a flaw, and discuss the method of separating the MFL signal of a superimposed defect near pipeline heads. The difference between reference signal and artificial flaw signal can be extracted properly by using the methodology of correlation canceling. 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