Nondestructive Eddy Current Testing

When a coil is placed in proximity to a conductor, the magnetic field in the vicinity of the coil is altered by eddy currents in the conductor. The conductivity of a sample material may be determined by measuring the field. Closed-form solutions are presented for the magnetic field at the surface of a semi-infinite conductor for two cases: a semi-infinite coil, the end of which is in contact with the conductor, and a loop of wire on the surface of the conductor.     

Comparison of Error Estimators in Eddy Current Testing

In this paper we present the comparison of error estimators using in 3-D magnetoharmonic FE model dedicated to eddy-current testing. The first error estimator is based on the nonverification of the behaviour law. This estimator is very accurate but requires the solution of both complementary formulations. The second estimator is based on an energetic approach using the Poynting vector in conductive regions and using the variation of the magnetic energy in nonconductive regions. Both estimators are tested within an adaptive meshing procedure and the results are compared with experimental results.      

3-D Eddy Current Computation in Carbon-Fiber Reinforced Composites

We propose a model for 3-D eddy current computation in carbon-fiber reinforced composites, where only the active parts are discretized. The proposed method is based on the ${rm T}-varphi$ formulation. We use the finite difference method in the composite material, associated to a volume integral equation in the source region where a current source density is imposed. As a validation, numerical results are compared to analytical calculation, supported by a numerical example in eddy current nondestructive testing.      

电磁涡流检测技术在天然气管道检测中的应用

为保证在役油气管道的安全运行,各种管道检测方法及其对管道适用性的研究成为研究热点.为了研究电磁涡流检测技术在小管径、低压低流速管道检测中的适应性,制定了 一套完整的检测方案,进行工程对象管道的试点检测,分析了目标管道内部金属损失深度分布情况,采用C扫、DR法对管道进行开挖验证,并结合检测所获取的数据,对缺陷进行完整性评...     

Lorentz Force Eddy Current Testing: a Prototype Model

We report an investigation of the motion of a free-falling permanent magnet in an electrically conducting pipe containing an idealized defect. This problem represents a highly simplified yet enlightening version of a method called Lorentz force eddy current testing which is a modification of the traditional eddy current testing technique. Our investigation is a combination of analytical theory, numerical simulation and experimental validation. The analytical theory allows a rigorous prediction about the relation between the size of the defect and the change in falling time which represents the central result of the present work. The numerical simulation allows to overcome limitations inherent in the analytical theory. We test our predictions by performing a series of experiments. We conclude that our theory properly captures the essence of Lorentz force eddy current testing although a refinement of the experiment is necessary to reduce the discrepancy to the predictions. In spite of its apparent simplicity the present system can serve as a prototype and benchmark for future research on Lorentz force eddy current testing.     

一种应用于涡流检测的DDS正交信号源

介绍了采用单片DDS芯片AD9854设计的频率可连续调节的宽带正交信号源，给出了系统的硬件构成、软件流程及软件编程方法等。该正交信号源具有优良的频率准确度，两路输出信号正交性好，且频带范围宽，应用在智能涡流无损检测中较好地解决了激励信号源及正交锁相放大器检测电路中参考源的问题。     

微波低通高阻频率选择复合材料的设计研究

采用数值法设计了8～12GHz(X波段)具有高反射同时2～4GHz(S波段)具有高透射的频率选通复合材料.采用有限元法(FEM)计算了含导电纤维复合材料的传输和反射系数,并用自由空间法对所制备的多层凯夫拉(Kevlar)纤维增强的复合材料样板(424mm× 424mm)进行测量.测量结果与计算结果具有良好的一致性.同时发现复合材料基材的介电特性和所嵌入金属纤维的电导率对材料的传输损耗有很大影响.     

Scanning SQUID Microscope NDT System Based on Eddy Current Testing

A scanning SQUID microscope based on HTS dc SQUID has been developed. The SQUID is mounted inside the insulation vacuum of a cryostat, which is separated from room temperature samples by a 65 μm thick sapphire window. Operating with a double-D exciting coil, it could be assembled to a scanning SQUID microscope Nondestructive Testing (NDT) system based on eddy current testing. The current is excited by an appropriate sinusoidal alternating (double-D coil) current in the conducting material, and then it induces a corresponding magnetic field. The vertical component of the field is then detected by the scanning SQUID system. The distortion of the field could be detected at the regions of discontinuities, such as flaws. Thereby, the defects inside the materials will be detected with neither contact nor destruction.     

Fast Analytical Modeling of Eddy Current Non-Destructive Testing of Magnetic Material

This article presents the modeling of non-destructive testing systems containing magnetic materials using a fast numerical method. Its main aim consists of correcting the half analytical expression of the impedance variation, formulated by some authors, caused by the presence of a conducting plate below of an absolute ferrite core probe. The obtained results of this correction are found to be consistent and satisfactory comparatively to those of finite element method. It also deals with the study the method rapidity by comparing its simulation time to that of the finite element method. As result, the proposed method is found to be very fast and a very short simulation time is required to calculate the sensor impedance. Indeed, for the studied system the coupled circuit simulation time is lower than 1.09 s. This study is appreciable, since it permits to solve quickly the inverse problem by expressing the physical and geometrical features of the material or defect according to the measured parameters. More importantly, this method is applicable to any axi-symmetric systems and can be adapted for the simulation of three-dimensional configurations.     

A New Approach for Optimal Design of Eddy Current Testing Probes

The optimal design of ECT probes for advanced nondestructive inspection of steam generator tubing in nuclear power plants is studied in this paper. A new approach for probe design is proposed, on basis of both a simplified detectability analysis method and a ring current model newly developed by the authors. The new approach is incorporated in the optimization of pick-up arrangements as well as the corresponding excitation coils. Two designs of a potential ECT probe which may show high performance in practical applications are proposed finally. In addition, the ring current model and the simplified detectability analysis method are validated further for a conducting tube by comparing the magnetic field perturbation due to a crack and the S/N ratios evaluated by the present method and an FEM-BEM hybrid code respectively. Consequently, the validity of the new design approach and the high performance of the new probe designs are assured.     

Study of the Choice of Excitation Frequency for Sub Surface Defect Detection in Electrically Thick Conducting Specimen Using Eddy Current Testing

Understanding the scope and limitations of non-destructive testing procedure is essential for selecting the appropriate test parameters for material inspection. This paper presents the scope of material (\( \delta_{s} \)) and probe dependent (\( \delta_{t} \)) penetration depths for determining the optimal test frequency (\( f_{opt} ) \) for detection of sub surface defects in electrically thick conducting specimens. Numerical modelling is carried out for a pancake coil above an electrically thick aluminium plate, \( t/\delta_{t} \)?>?1, to study the influence of the EC probe and defect location (\( t_{df} \)) on the test frequency for near and deep sub surface defects. The study concludes that the optimal test frequency, \( f_{opt} \) for detection of deep sub surface defects (\( t_{df} /t \approx 1 \)) is determined by the probe dependent skin depth, \( \delta_{t} \), and the plate thickness is related to \( f_{opt} \) by, \( t \propto 1/\sqrt {f_{opt} } \). The numerical observations were experimentally validated for machined sub surface notches on a 10 mm thick (\( t \)) aluminium plate.     

Analytical Modeling of Wobble in Eddy Current Tube Testing with Bobbin Coils

By utilizing the second-order vector potential formulation we solve the eddy current problem of a coil inside a conductive tube and in an offset position to it. The study focuses on the derivation of a closed-form expression for the impedance change of the coil, which is used to calculate the signal produced by wobble in eddy current testing of tubes with bobbin coils.     

基于涡流信号的应力腐蚀裂纹区域电导率特性研究

对应力腐蚀裂纹进行涡流检测定量重构时,因裂纹区域电导率特性尚不明确,影响了裂纹的定量精度.本文将裂纹考虑成由多个等厚层组成的模型,采用高频涡流检测仪器和高精度涡流检测数值模拟程序对应力腐蚀裂纹区域的电导率特性进行了分层研究.通过计算和实验,初步验证了检测方法的可行性,并给出了应力腐蚀裂纹电导率值初步结果.     

Analytical Modeling of Wobble in Eddy Current Tube Testing with Bobbin Coils

Abstract

By utilizing the second-order vector potential formulation we solve the eddy current problem of a coil inside a conductive tube and in an offset position to it. The study focuses on the derivation of a closed-form expression for the impedance change of the coil, which is used to calculate the signal produced by wobble in eddy current testing of tubes with bobbin coils.     

The Application of Eddy Current Transducer for Testing Movement Locus of Shaker Screen

Shaker screen is one of important equipments in the industry of oil,metallurgy,coal and timbering． The movement locus of shaker screen affects the capacity and efficiency of shaker screen to split the solid particle from crude ore directly．To test movement of shaker locus,two eddy current transducers are employed． A discussion of the usage of these eddy current transducer to test and acceleration sensors will be made．The experiment results from a real elliptic shaker screen have good agree with the design requirements．     

考虑磁导率非线性的铁磁材料脉冲涡流检测仿真研究

长期以来,脉冲涡流检测中铁磁材料的磁导率多被视为常数,但这种简化的合理性及其影响尚缺乏充分的证明.本文基于有限元法,建立了探头置于Q235钢板上方的脉冲涡流检测模型,研究了钢板磁导率的空间分布和时间变化规律及其对探头信号的影响,并进行了实验验证.结果表明:钢板中瞬态磁场的工作点与激励电流幅值有关,增大激励电流,磁场可能超出磁化曲线的起始磁化区而进入到瑞利区甚至陡峭区;由于磁导率非线性的影响,激励方波高、低电平段的感应电压信号不成奇谐对称,高电平段的晚期感应电压比低电平段的大;钢板浅层磁导率的变化显著,不能简化为常数,而深层的磁导率变化很小,可视为常数.     

基于脉冲涡流检测技术的缺陷定量检测研究

对飞机多层结构中出现的缺陷进行定量检测具有重要意义.文章将脉冲涡流检测技术应用其中,设计并实现了一套完整的脉冲涡流检测系统.在对检测信号进行分析处理的基础上,提取峰值、峰值时间、过零时间等时域特征量,实现对缺陷的定量检测,并通过进一步的实验加以验证.     

Method for Removing Secondary Peaks in Remote Field Eddy Current Testing of Pipes

In the remote field eddy current (RFEC) testing of pipes, because the remote eddy current penetrates the pipe’s wall twice, the testing results exhibit two peaks (primary peak and secondary peak) that originate from both the transmitter and receiver passing by the same place in the pipe. The secondary peaks have the same features as the primary peaks that are used to assess defects, and if there is no separation between primary peaks and secondary peaks, incorrect evaluations of defects will be obtained. Considering the benefits of removing secondary peaks in RFEC testing, dual receivers are taken into account. Dual receivers are set in remote fields and are set coaxially to the transmitter to obtain differential signals at the same time. In the proposed method, position dependent response of the differential signals from the dual receivers is calibrated, a Wiener deconvolution filter is used to identify secondary peaks and filter testing noise, and the factors that affect results of removing secondary peaks are also analyzed. To validate the feasibility of the proposed method of RFEC testing, ANSYS is made use of when setting up the analysis model, and an experimental pipe is designed to be identical to ANSYS model. The results of the analysis of ANSYS and experiments both validate the practicality of the proposed method and show the benefits of simplifying the analysis of RFEC signals.