焊缝小角度裂纹缺陷的磁轭法检测

在对锅炉的C类焊缝进行磁粉检测时,发现了与焊缝轴线夹角〈30°的线状缺陷,而在理论上来说此类缺陷很难检测出来。进行了磁轭检测试验,通过磁粉指示磁力线以及磁轭悬空时的磁力线检测试验,说明在进行焊缝磁轭检测时,在空间位置有限的情况下,若磁场强度足够,仍然可以检测到磁轭触头周围的缺陷,但要注意区分相关显示和非相关显示。     

应力对漏磁信号的影响

根据最新力磁理论，使用微型霍尔探头对R3碳钢进行漏磁检测。分析了在弱磁场和强磁场下施加应力后材料的漏磁信号变化。指出残余应力作用下中碳钢的漏磁信号会发生剧烈变化以及应力和漏磁信号之间的联系。预言了对应力集中进行漏磁检测的可行性。     

基于三维有限元的平行钢丝拉索断丝漏磁场仿真

随着桥梁检测技术的发展,漏磁检测技术开始应用于在役拉索检测。由于拉索自身结构复杂,拉索漏磁检测具有大直径和大提离的特点,导致背景磁场较强。利用有限元方法建立三维漏磁检测模型,通过将存在断丝缺陷的磁场信号与无缺陷的磁场信号求差,获得了真实漏磁场信号;研究了断丝断口宽度、埋藏深度等参数对检测信号的影响,给出了漏磁场随上述参数的变化曲线,从而为拉索漏磁检测信号的解释提供依据,为断丝量化分析奠定了基础。     

Mechanical damage detection using magnetic flux leakage tools: modeling the effect of dent geometry and stresses

We have used three-dimensional (3D) magnetic finite element analysis (FEA) to simulate the MFL signal from a circular dent geometry with associated residual stresses. Strain distribution information around the dent was obtained from an earlier work using finite element structural modeling. In the magnetic FEA dent model, the localized residual stresses were simulated by assigning appropriate values of magnetic anisotropy to the relevant magnetic regions. The simulated flux leakage patterns were found to be in good agreement with the experimentally observed MFL patterns associated with dent shape as well as with the stress effects from the dent.     

磁粉检测中交叉磁轭的灵敏度探讨

磁粉检测中,为了保证检测的灵敏度,交叉磁轭复合磁化检测采用连续移动的方式进行工件磁化,而不采用步进式检测。笔者在实际检测工作中发现,交叉磁轭灵敏度与仪器采用的励磁方式有关系,采用步进式进行检测,也能够有效地检出缺陷。为此,通过对CDX-IY型便携式磁粉探伤仪的励磁方式的分析,对交叉磁轭复合磁化的检测灵敏度进行了探讨。分析表明,在交叉磁轭形成的复合磁场中,除了形成旋转磁场外,在通电开始和通电结束的5 ms时间,两交叉磁轭分别作为单相磁轭,产生单相磁场。交叉磁轭所覆盖的这一区域,既有单相磁场,又有复合磁场综合作用,因此,采用步进式进行检测,其灵敏度可以保证。     

Online nondestructive testing for fine steel wire rope in electromagnetic interference environment

The diameter of fine steel wire rope (FSWR) is generally a few millimeters. Its magnetic flux leakage (MFL) signal is weak, and the number of magnetic sensors installed for defect detection is limited because of the small diameter. In FSWR production workshops, different kinds of machinery work together, deteriorating the power quality and making the spatial electromagnetic environment complex; the weak MFL is thus interfered with further. It is difficult to carry out online nondestructive testing (NDT) of FSWR in the process of manufacturing. In this paper we present a novel MFL method for FSWR NDT in a strong electromagnetic interference environment. We use a three-dimensional finite element method (FEM) to analyze the MFL signals. A simplified magnetic circuit is presented to excite the FSWR; the circuit comprises two half-sized radial magnetizing ring NdFeB magnets, and because there is no need for a magnetic yoke, the device is simple and light. A single Hall sensor is used to measure the flux leakage field. A stable performance power system is designed for the NDT power supply, which is not only resistant to voltage sags, but also has very low output noise. To enhance the signal-to-noise ratio (SNR) of the MFL defects signal, a signal conditioning and processing circuit are designed to enhance the detectability of signals in MFL data. The novel and small FSWR NDT system realizes on-line testing in an environment of strong electromagnetic interference, and for the experiment with a 1.5-mm-diameter wire rope twisted by 19 wires, the minimum damage of a pit on half of a wire can be identified.     

Velocity effect analysis of dynamic magnetization in high speed magnetic flux leakage inspection

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.     

Experiment and simulation study of 3D magnetic field sensing for magnetic flux leakage defect characterisation

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.     

Characterization of texture and residual stress in a section of 610 mm pipeline steel

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.     

铁磁性材质铝翅片管的在役检测

铁磁性材质铝翅片管的在役检测是各种换热器管检测中难度最大的检测之一，常用的检测技术无法应用。为了找出其适用的在役检测方法，尝试了两种新的检测技术，即漏磁检测技术和超声内壁旋转检测技术，通过对带有人工缺陷的试样管分别进行检测试验，发现该两种技术应用于铁磁性材质铝翅片管检测的可行性和优缺点，最后结合试验结果进行分析，总结出铁磁性材质铝翅片管适用的在役检测方法。     

压力容器无损检测--漏磁检测技术

简要介绍了漏磁检测技术的原理及其应用,概述了当前国内外的漏磁检测技术和仪器的发展现状以及在压力容器检验中的应用,分析了影响漏磁检测灵敏度的主要因素。     

管道漏磁法检测的ANSYS仿真研究

采用有限元分析法对管道漏磁法检测的漏磁场理论进行了研究,通过有限元分析可以对各种情况下管道壁缺陷的漏磁情况进行仿真,弥补了磁偶极子模型解析法的局限性。还介绍了有限元分析软件ANSYS分析管道漏磁场的过程,并通过ANSYS分析研究了提离值对漏磁信号的影响,并进行了漏磁检测器磁化装置的优化设计。     

Composite magnetic flux leakage detection method for pipelines using alternating magnetic field excitation

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.     

Development of a magnetic sensor for detection and sizing of internal pipeline corrosion defects

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.     

利用磁屏蔽效应改善钻杆漏磁检测信号信噪比

为了高效率地检测油田钻杆,设计了磁屏蔽器,电磁有限元分析表明,有磁屏蔽器存在时,钻杆漏磁信号将明显集中于缺陷附近,且永磁体元件之间通过空气介质耦合的背景磁通会大大降低。钻杆实物漏磁测试证实了这一分析结果,配有磁屏蔽器的探头可明显提高漏磁信号信噪比,有利于提高缺陷漏磁识别率。     

便携式管道漏磁检测系统

结合漏磁检测、信号处理和单片机技术，研制一种低功耗的便携式漏磁检测装置。详细介绍系统各部分的功能。测试表明，此装置通过沿管道轴向一次扫查可以全面、快速地检测出管道内外壁缺陷。该系统可广泛地应用于工业管道检测。     

钢轨表面缺陷漏磁检测的三维磁场分析

漏磁检测技术通常测量垂直和平行于缺陷表面的漏磁场分量,来实现对缺陷的定量分析。然而,对于钢轨表面的复杂裂纹,传统的方法很难准确检测。为了克服这种检测方法存在的不足,采用三维磁场测量方法以及有限元法对缺陷漏磁场的三维分布情况进行了分析。在此基础上设计了一套适合钢轨表面缺陷检测的三维漏磁检测系统,并对人工缺陷样例进行了检测。结果表明,漏磁信号垂直分量包含重要的缺陷信息,特别是对于与钢轨走向不垂直的缺陷。     

A new MFL principle and method based on near-zero background magnetic field

On the basis of the analysis of the MCE (magnetic compression effect) in present MFL (magnetic flux leakage) applications, a new MFL principle and technique based on the establishment of a near-zero background magnetic field is proposed for the first time, resulting in an increase of MFL allowing a non-contact MFL signal pick-up at larger probe lift-off. Afterwards, the feasibility of the proposed principle is justified by simulations and experiments. Finally, their advantages are presented. By applying the proposed MFL principle, the severe wear of contact probes can be avoided and inspection at high-temperature heat pipes can be performed. The contributions of the technique to reduce magnetic noise, distortion and the saturation of hall sensors are also discussed.     

基于径向基函数神经网络的管道缺陷漏磁场分析

管道缺陷漏磁场的量化研究一直是个难题，提出了应用径向基函数（RBF）神经网络来对漏磁场插值计算和非线性逼近的必要性，建立了适合该问题的RBF网络模型，给出了学习算法，制作了常见的人工凹坑缺陷，并对其用该方法进行插值和漏磁场曲面重构。结果表明，该模型算法收敛速度快、自适应性强、所需数据量小、计算量少、拟和曲面效果好，能很好地反映缺陷漏磁场的分布，比其它插值方法更方便、有效，为管道缺陷检测量化提供了一种可行的方法。