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脉冲涡流检测技术在带包覆层管道腐蚀缺陷检测中展现出优势而引起广泛关注。本研究设计了一种脉冲涡流聚焦探头,通过有限元仿真与试验,研究其在复杂结构部位中的检测能力。仿真结果显示,设计的脉冲涡流聚焦探头能有效聚集磁场与涡流场能量,有利于对局部缺陷与复杂结构中的缺陷进行检测。通过探究聚焦探头在提离10~50 mm下对管道焊缝及各种尺寸局部缺陷的检测灵敏度,分析其检测能力与提离检测极限,以及在检测过程中的信号特征。结果表明,聚焦探头在提离50 mm下仍能检出尺寸为40 mm×40 mm×1 mm(长×宽×深)的方形局部腐蚀缺陷,焊缝信号的凸起特征、缺陷信号的下凹特征与仿真结果相印证。 相似文献
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以激光对接焊的焊接缺陷为对象,研究基于数值模拟的焊接缺陷漏磁场的分析方法. 建立对接焊焊接缺陷检测的三维模型,利用漏磁场理论对比分析不同几何缺陷与漏磁场信号之间的关系规律,并用试验进行验证. 结果表明,裂纹的深度越深,磁感应强度越大,未熔合、凹坑分别随着角度、宽度的增大而磁感应强度减小,并且验证漏磁场信号可以作为焊接缺陷检测的依据. 采用RGB分割法对磁光图像进行分割并提取几何特征,用模糊C-均值聚类(FCM)对不同焊接缺陷进行识别,有良好的识别率. 相似文献
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Eddy current probes are used extensively to evaluate the integrity of steam generator tubes in nuclear power plants and to detect cracks in tube walls. The probe design has evolved from simple bobbin probes to mechanically rotating multi-coil probes providing high resolution images of tube integrity. This paper presents a novel rotating field eddy current probe with bobbin pickup coil that generates a rotating magnetic field, thereby avoiding mechanical rotation of probe. Three balanced identical rectangular windings carrying excitation currents with 120° phase difference generate an electrically rotating magnetic field that is sensitive to defects of all orientations. A bobbin coil located in the center is used as a pick up sensor. The phase of induced voltage in the bobbin coil is interpreted in terms of the circumferential location of the defect. The properties of the probe are investigated using a three dimensional finite element model, and validated experimentally using measurements. 相似文献
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飞机多层结构铆钉周围埋藏裂纹检测是无损检测领域的一个难点和热点,脉冲涡流能够对这种裂纹进行有效的检测。针对这种缺陷检测,本研究采用了一种双激励线圈且用隧道磁电阻(TMR)为接收的新型探头。双激励源反向联接,激励电流不至于过大,但磁场却能达到局部聚焦的作用。通过大量试验对该传感器参数进行优化选择,以提高传感器的检测灵敏度。试验结果表明:当激励线圈绕制180匝、两激励线圈间距为20~30 mm、单个线圈水平夹角为60°~90°、且TMR位于裂纹正上方时探头的检测灵敏度最大。该研究结果可为飞机多层结构铆钉周围裂纹脉冲涡流检测探头设计提供参考。 相似文献
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在埋地金属管道检测领域中,常规检测手段多采取接触式的,检测前需要先对管道进行开挖或是停运,难以满足工业检测要求。而被动式弱磁检测技术可以实现对埋地管道的非开挖检测。本研究在介绍被动式弱磁检测技术原理的基础上,通过改变测磁传感器与管道垂直方向之间的距离来模拟管道的实际埋深,通过试验数据的分析可以得出磁场强度、管道埋深和腐蚀深度之间存在指数关系。在此基础上,结合磁场梯度变化和概率统计的原理可以得出缺陷判断的依据,即当磁场梯度在(μ-2σ,μ+2σ)区间外变化时可判定为缺陷。与常规检测手段相比,被动式弱磁检测技术无需人为对管道进行磁化。在管道非开挖条件下,可以对埋地金属管道腐蚀状况进行科学评估,并实现二维成像。 相似文献
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Magnetic flux leakage technique is used for defect detection inside a magnetically permeable bar by measuring the leakage fields outside the bar. Defects of varying sizes in a magnetically permeable bar have been modelled as localized anti-dipoles with different moments. These defect locations and moments have to be determined based on the measurement of the leakage fields in the presence of random noise. Multiple Signal Classification (MUSIC) approach has been used to identify the defect locations and the moments of these defects. After finding the location of the first dipole representing the larger defect, using orthogonal projection of the measured magnetic field data away from the first defect location, location of the next dipole is identified by MUSIC. This process is continued until all the defects are exhausted. The leakage fields from three deeply buried defects were simulated by direct forward calculation and the resulting data were utilized for inversion using this approach. It has been possible to identify the number of defects and their locations by this approach even in the presence of reasonable levels of additive noise. 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 surface magnetic field measurement (SMFM) technique has proved to be an accurate means for crack detection and sizing cracks in ferrous metals. The technique involves the use of two U-shaped current-carrying wires of sufficiently high frequency while measuring the discontinuity in the resultant magnetic field at the crack edge with an appropriate magnetic field sensor. In this work, we describe a mathematical algorithm to obtain the crack signal from the output of an induction coil used in a SMFM probe. We also discuss the measurement errors due to the coil size and shape. To reduce the measurement errors, we present an algorithm in which the crack signal is recovered by appropriate deconvolution of the coil output signal and its spatial transfer function. The algorithm is then used to recover crack signals for various coil shapes and sizes. The study of the results demonstrates the effectiveness of the algorithm in the case of large coils. 相似文献
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On the basis of permanent magnet, perpendicular oriented to the surface of the component under inspection and surrounded by a pick-up coil, the so-called PMFP-effect (permanent magnetic field perturbation-effect) can be observed when the magnet is moved in this perpendicular position with a well defined lift-off along the surface and a surface-breaking or near-surface – but hidden – defect is coming into the influence range of the magnetic field. A new NDT (nondestructive testing) technique by using PMFP so can be proposed for the first time, and its detection mechanism is presented and analyzed by simulations. Afterwards, its testing characteristics for defects are given and its feasibility is further confirmed by experiments. Meantime and particularly, its inspection depth and the effect of the position and attitude of PMFP sensors on inspection signals are analyzed. Accordingly, a multi-differential method used for improving signal-to-noise rate is presented and some testing apparatus using PMFP method is developed. Finally, the proposed PMFP method is discussed specially compared to MFL in detail. 相似文献
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In the present study, two types of ferrite core probes were prepared with different pick-up coil positions for remote field eddy current testing. One probe has a pick-up coil on the beam of the U-type ferrite core, and the other probe has a pick-up coil on the pole of the U-type ferrite core. The two types of probes were examined for their capability to create an effective remote field to detect a back-side defect. The results showed that the pick-up coil at the pole of the U-type ferrite core can detect an effective remote field phenomenon. In addition a time harmonic analysis was carried out, and the flow of the magnetic flux of the direct field was used to analyze the difference in the results with the two probes.The detectability for back-side flaws was confirmed with the proposed probes. Compared to a previous study, the signal measured from back-side flaws with the type II probe was large. However, the signal-to-noise (SN) ratio for the detection of back-side flaws did not improve because of the different background signal before and after the back-side flaw. 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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This paper reports the use of a non-destructive, continuous magnetic Barkhausen noise (CMBN) technique to investigate the size and thickness of volumetric defects, in a 1070 steel. The magnetic behavior of the used probe was analyzed by numerical simulation, using the finite element method (FEM). Results indicated that the presence of a ferrite coil core in the probe favors MBN emissions. The samples were scanned with different speeds and probe configurations to determine the effect of the flaw on the CMBN signal amplitude. A moving smooth window, based on a second-order statistical moment, was used for analyzing the time signal. The results show the technique's good repeatability, and high capacity for detection of this type of defect. 相似文献
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Pingjie Huang Guangxin Zhang Zhaotong Wu Jinhui Cai Zekui Zhou 《NDT & E International》2006,39(7):578-584
The forward problem of eddy current detection of defects by scanning conductive multi-layered structures is investigated and the change of the probe coil impedance is modeled by using finite element analysis method. Based on the ANSYS software a fast simulating program is developed and then the coil impedance changes due to the existing of defects in different lengths, shapes and at different locations in conductive multi-layers are calculated. An experimental eddy current testing system combined with a scanner is established and scanning testing experiments are carried out. The simulation and experimental results are compared. The agreement of them shows that the technique studied is promising and can help us to understand the probe responses and can be applied to the inversion model to determine the defect parameters in many important fields ranging from aerospace to energy and transportation industries. 相似文献
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基于LabVIEW的远场涡流管道检测系统 总被引:1,自引:0,他引:1
为了提高管道无损检测的精度,实现管道内外壁缺陷的检测,采用远场涡流的检测方法,依据检测线圈接收到的信号是激励线圈产生磁场两次穿过管壁后的信号,携带了管壁内外缺陷信息的原理,设计了远场涡流传感器、检测信号处理电路。对检测线圈接收信号进行放大、滤波处理,信号采集;采用LabVIEW编程计算检测信号幅值,互相关算法计算检测信号相位,确定缺陷深度。对内径36mm的有伤管道进行了试验。结果表明,所设计的仪器能检测出管道上深度为0.5mm及以上缺陷。利用LabVIEW对相位差计算提高了检测精度,为实际应用提供参考。 相似文献
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This paper describes analytical expressions for the magnetic leakage field of two types of internal defects: two dimensional rectangular and elliptical defects as functions of the applied magnetic field strength, the defect size and the distance below the surface. In this study, the magnetic image effects from the spatial boundary and the defect boundary are taken into consideration. That is, the leakage field of rectangular-like defects or elliptically shaped defects ‘below the surface’ are derived by using the modified dipole model and image theory. The profiles and strengths of leakage fields calculated from the proposed analytical forms are presented under various conditions and compared with experimentally measured ones. 相似文献
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The distribution of a magnetic field over an inductor used for sheet castings has been investigated experimentally. With an increase in height from the surface, the magnetic field density decreases according to the exponential law. In the transverse direction, the magnetic field density is approximately uniform except near the edges. The magnetic field density is direct proportional to the number of turns multiplied by the current in amperes. Ferromagnetic material in the upper mould can enhance the magnetic field density. Under the electromagnetic force, the mould-filling process of sheet casings has been studied by physical simulation method. The difference in filling capability between gravity casting and travelling magnetic field casting has been studied. The electromagnetic force can enhance the filling process, but it also brings a problem. With an increase in the magnetic field density, the surface quality of the aluminum alloy sheet castings becomes poor. The reason is discussed. 相似文献