Absolute Wall Thickness Measurement of Conducting Plates Using Pulsed Eddy Currents

The method using pulsed eddy currents to determine the thickness of a conduction plate is extended to enable the simultaneous measurement of the plate thickness and material properties. For optimal performance, a probe must be designed depending on the thickness range that should be accessible. The need for a calibration of the material properties of a conducting plate to enable the measurement of its thickness has been removed. All that is needed is a probe with known dimensions and suitable hardware to create a current pulse and measure a transient magnetic induction.

ARRAY PULSED EDDY CURRENT IMAGING SYSTEM USED TO DETECT CORROSION

A theory model is established to describe the voltage-current responsefunction. The peak amplitude and the zero-crossing time of the transient signal is extracted as theimaging features, array pulsed eddy current (PEC) imaging is proposed to detect corrosion. The testresults show that this system has the advantage of fast scanning speed, different imaging mode andquantitative detection, it has a broad application in the aviation nondestructive testing.

Inverse problem of pulsed eddy current field of ferromagnetic plates

To determine the wall thickness, conductivity and permeability of a ferromagnetic plate, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy current testing on the plate. From time-domain analytical expressions of the partial derivatives of induced voltage with respect to parameters,it is deduced that the partial derivatives are approximately linearly dependent. Then the constraints of these parameters are obtained by solving a partial linear differential equation. It is indicated that only the product of conductivity and wall thickness, and the product of relative permeability and wall thickness can be determined accurately through the inverse problem with time-domain induced voltage. In the practical testing, supposing the conductivity of the ferromagnetic plate under test is a fixed value, and then the relative variation of wall thickness between two testing points can be calculated via the ratio of the corresponding inversion results of the product of conductivity and wall thickness. Finally, this method for wall thickness measurement is verified by the experiment results of a carbon steel plate.

Analytical solutions of transient pulsed eddy current problem due to elliptical electromagnetic concentrative coils

The electromagnetic concentrative coils are indispensable in the functional magnetic stimulation and have potential applications in nondestructive testing. In this paper, we propose a figure-8-shaped coil being composed of two arbitrary oblique elliptical coils, which can change the electromagnetic concentrative region and the magnitude of eddy current density by changing the elliptical shape and/or spread angle between two elliptical coils. Pulsed current is usually the excitation source in the functional magnetic stimulation, so in this paper we derive the analytical solutions of transient pulsed eddy current field in the time domain due to the elliptical concentrative coil placed in an arbitrary position over a half-infinite plane conductor by making use of the scale-transformation, the Laplace transform and the Fourier transform are used in our derivation. Calculation results of field distributions produced by the figure-8-shaped elliptical coil show some behaviours as follows： 1） the eddy currents are focused on the conductor under the geometric symmetric centre of figure-8-shaped coil; 2） the greater the scale factor of ellipse is, the higher the eddy current density is and the wider the concentrative area of eddy current along y axis is; 3） the maximum magnitude of eddy current density increases with the increase of spread angle. When spread angle is 180°, there are two additional reverse concentrative areas on both sides of x axis.

Research on the Crack Detection of Conductive Components Using Pulsed Eddy Current Thermography

Crack of conductive component is one of the biggest threats to daily production. In order to detect the crack on conductive component,the pulsed eddy current thermography models were built according to different materials with the cracks based on finite element method(FEM) simulation. The influence of the induction heating temperature distribution with the different defect depths were simulated for the carbon fiber reinforced plastic(CFRP) materials and general metal materials. The grey value of image sequence was extracted to analyze its relationship with the depth of crack. Simulative and experimental results show that in the carbon fiber reinforced composite materials,the bigger depth of the crack is,the larger temperature rise of the crack during the heating phase is; and the bigger depth of the crack is,the faster the cooling rate of the crack during the cooling phase is. In general metal materials,the smaller depth of the crack is,the lager temperature rise of the crack during the heating phase is; and the smaller depth of the crack is,the faster the cooling rate of crack during the cooling phase is.

Image-Based Feature Extraction Technique for Inclined Crack Quanti cation Using Pulsed Eddy Current

Existing eddy current non-destructive testing(NDT) techniques generally do not consider the inclination angle of inclined cracks, which potentially harms a larger region of a tested structure. This work proposes the use of 2 D scan images generated by using pulsed eddy current(PEC) non-destructive testing(NDT) technique in the quantification of the inclination and depth of inclined cracks. The image-based feature extraction technique e ectively identifies the crack axis, which consequently enables extraction of features from the extracted linear scans. The technique extracts linear scans from the images to allow the extraction of three novel image-based features, namely the length of extracted linear scans(LLS), the linear scan skewness(LSS), and the highest value on linear scan(LSmax). The correlation of the three features to surface crack inclination angles and depths were analysed and found to be highly dependent on the crack depths, while only LLS and LSS are correlated to the crack inclination angles.

Combination of eddy current and heat treatment for crack healing and mechanical-property improvement in magnesium alloy tube

The continuous eddy current pulse treatment(ECPT)combined with heat treatment was employed to heal the microcracks in spin formed Mg alloy tubes and improve their mechanical properties in this study.The results show that all the microcracks in different tube specimens were almost healed after different continuous ECPT schemes up to 15 cycles.The schemes with less cooling intervals exhibited better healing effect and increased the strength and elongation of Mg alloy tubes more obviously.After aging treatment,the strength improvement of the specimens with ECPT was more remarkable than that of the specimens without ECPT,and the elongation decrease of the specimens with ECPT was less evident than that of specimens without ECPT due to the segregation of RE elements on the crack surface.Besides,after solution treatment,the strength reduction and ductility improvement of the specimens with ECPT were more pronounced than that of the specimens without ECPT owing to the notable decrease of dislocation density of the specimens with ECPT.Both narrowed cracks induced by ECPT and the segregation of precipitates in the vicinity of microcrack surface during aging treatment contributed to the maximum strength in the as-spun specimens with ECPT followed by aging treatment.

带包覆层承压设备的PECT应用研究

特种设备如压力容器、压力管道等,在石油、精细化工、火电、核电等行业得到了大规模应用;其安全健康运行对于保障装置的稳定生产具有重要作用。采用脉冲涡流检测(PECT)技术可对设备包覆层下存在的内外壁腐蚀缺陷进行快速在线检测,对于保障核心设备的本质安全有着重要意义。介绍了带包覆层承压特种设备的脉冲涡流检测应用研究背景,并对带包覆层承压特种设备PECT技术原理进行了介绍。通过对比试验,对PECT检测探头结构进行了深入研究,总结出U形磁芯探头具有更加良好的检测灵敏度;通过试验观察,相邻金属构件和金属保护层搭接位置是PECT结果主要的干扰因素,通过对探头施加金属屏蔽层可有效滤除周边金属构件干扰,同时发现铁磁性材料的金属保护层搭接的干扰信号难以去除;现场实际应用案例,证明了PECT技术对带包覆层承压设备腐蚀具有良好的适用性。

PECT在铁磁性材料测厚中传感器参数分析

脉冲涡流检测中激励参数与传感器参数对检测信号影响较大,分析不同参数对检测信号的影响规律,进而优化设计可提高检测系统的性能。基于脉冲涡流检测原理,建立脉冲涡流铁磁性试件测厚试验系统,分析激励线圈匝数与线圈内径对检测信号的影响规律。试验结果表明,增大激励线圈匝数与线圈内径可提高检测信号分辨率;线圈内径与激励线圈匝数的增加可提高检测信号最小值数量级;通过增加激励线圈匝数与线圈内径可提高传感器的检测厚度范围。

单DC/DC升压型便携式PECT电源系统设计

为进一步满足脉冲涡流热成像(PECT)现场检测的应用需求,提出一种改进型“锂电池+超级电容”复合结构供电的便携式脉冲涡流热成像电源系统。通过分析两种串联式拓扑结构,采用“单DC/DC升压”结构来提升系统功率输出能力,同时搭建便携式检测系统,并详细介绍了激励电源控制策略,对便携式系统样机实验平台进行实验验证。实验表明,便携式电源系统的最大输出功率为1.9 kW,连续工作时间为1.1 h,系统样机净重为8.4 kg,该系统设计可较好地满足现场检测的需求。

Pulsed electromagnetic non-destructive evaluation and applications

This paper introduces recent research work in the field of pulsed electromagnetic non-destructive testing/evaluation.These are pulsed eddy current,pulsed magnetic flux leakage and eddy current pulsed thermography.This paper introduces pulsed electromagnetic techniques and their different case studies on defect detection as well as stress characterisation.Experimental tests have been validated and future research plans are discussed.This paper demonstrates pulsed electromagnetic non-destructive testing and evaluation for not only depth information,but also for multiple parameter measurement and multiple integration,which are important for future development.

基于PECT的金属保护层重合处干扰研究

对实际工业现场的有包覆层设备开展脉冲涡流检测(PECT),发现包覆层的外部金属保护层搭接重合处对检测结果造成干扰;利用试验手段,分别在金属保护层采用非铁磁性材质的铝皮及铁磁性材质的白铁皮条件下进行干扰试验;研究结果表明,当金属保护层为铝皮时,各段保护层搭接重合处引起的干扰信号可通过直接观察检测结果的晚期时窗信号直接进行滤除,不影响缺陷的检出;而当金属保护层为白铁皮时,由各段保护层搭接重合处引起的干扰信号无法滤除,故当缺陷位于重合处时则无法检测.

基于脉冲涡流监测与Wiener过程的再制造工作辊实时剩余寿命预测方法

再制造工作辊在热轧工作过程中熔覆层易发生复杂的退化行为,而其性能退化会影响轧制产品的质量。为实时监测轧辊退化情况并预测其剩余寿命,构建一套在线脉冲涡流监测方法和系统,采用变分模态分解-希尔伯特变换(VMD-Hilbert)方法提取0~5000 Hz频率边际谱能量和的增量作为轧辊退化特征。基于此,构造考虑个体差异的状态退化空间模型,结合最大期望(EM)算法和Kalman平滑滤波算法联合对模型中未知参数进行自适应参数估计,并利用层次分析法融合监测的历史数据与实时数据,以实现对再制造工作辊实时剩余寿命预测。实验结果表明,所提方法能够准确预测再制造工作辊剩余寿命,具有一定的应用前景。

脉冲涡流缺陷检测理论与技术研究综述

由于具有非接触、效率高、检测信号的信息含量丰富等诸多优点,脉冲涡流技术被广泛应用工业产品的缺陷检测,尤其是带包覆层、异质、以及多层导电结构等检测难度极大的工业产品。脉冲涡流探头结构的设计和优化是提高检测灵敏度和准确度的关键,目前大量的研究工作围绕探头结构的设计和优化开展;不同材质、结构、以及缺陷类型或形状需要选用合适特征量表征,特征量的选取与分析也是脉冲涡流技术研究的关键;另外,由于脉冲涡流检测信号受提离高度影响极大,未知提离高度的缺陷准确检测面临极大的挑战,因此提离效应的抑制也是研究的重点之一。本文从探头的设计与开发、特征量的选取与分析、提离效应的抑制等方面,对脉冲涡流检测技术的研究进展进行综述。同时,为更好的推动脉冲涡流检测技术发展,论文在现有的研究基础上,对脉冲涡流探头设计、特征量分析、以及提离效应抑制等进行了展望。

脉冲电磁式EMAT-涡流检测复合系统的研究

常规电磁超声换能器(EMAT)中永磁体难以应用于实际情况、产生的信号幅值较小,根据电磁超声检测和涡流检测在检测范围内的互补性,本文设计了脉冲电磁式EMAT—涡流检测复合传感器结构,采用多物理场耦合技术验证了复合检测方法的可行性,并讨论了影响传感器检测灵敏度的关键参数。结果表明:该复合传感器能够激发用于检测表面缺陷的涡流信号和检测深层缺陷的超声波信号,并且对不同宽度和深度缺陷具有良好的灵敏度;此外,对励磁线圈与涡流线圈进行参数优化设计,为电磁超声和涡流的复合检测应用提供思路。

脉冲涡流检测中核电运行机组电磁干扰研究

脉冲涡流主要应用于壁厚的腐蚀检测工作,因其可在带保温的情况下进行检测工作而受到无损检测行业的关注。由于脉冲涡流对于在役运行的核电机组的检测,更容易受到电磁环境的干扰,研究从脉冲涡流检测信号的频谱分析入手,论证了核电在役机组低频电磁场干扰对检测信号的强干扰作用。研究在役机组空间电磁干扰的频谱识别,并通过实验验证了其对脉冲涡流时域检测信号的影响。根据研究结果,提出用检测信号与空间参考信号作差,来消除空间电磁干扰的差分检测模式,可较好地抑制在役机组的电磁干扰问题。在核电机组运行状态下,通过现场实验验证了探头差分模式下脉冲涡流在役检测效果。

在役油管内壁腐蚀缺陷脉冲涡流检测方法

为实现采油管柱中的在役油管内壁腐蚀缺陷高精度离线检测,本文提出了一种基于双磁场传感的脉冲涡流外检测及深度定量评估方法。在试验研究中,以检测信号下降沿对数曲线斜率作为信号特征。在建立信号特征与油管剩余壁厚间映射关系的基础上,通过分析感应涡流在油管内分布范围与成像检测所识别腐蚀缺陷区域间的互相关关系,引入腐蚀缺陷深度评估补偿系数β。结合所建立映射关系,形成油管内壁腐蚀缺陷深度高效可视化定量评估方法。通过对缺陷成像及深度定量评估结果与真实情况的对比分析发现:所提方法不仅可实现对油管内壁腐蚀缺陷的三维形貌重现,且对其深度的定量评估具有较高的精度,满足工程实际在役油管的检测精度要求。

基于磁场梯度感测的旧油管腐蚀缺陷脉冲涡流可视化检测

油管是油气井管柱中用于直接汲取石油、天然气的最内部管道。服役中的油管长期接触含硫物质,其内壁会出现腐蚀缺陷,影响管柱完整性。基于磁场梯度感测,提出一种结合双传感器差分机制的脉冲涡流检测探头,以实现旧油管内壁腐蚀缺陷的高灵敏度成像。在确定检测探头构型的基础上,通过系列试验,探究下降沿对数曲线斜率和归一化差分信号峰值两类信号特征与腐蚀缺陷尺寸间的关联规律;同时,基于两类信号特征探索腐蚀缺陷成像方法。提出了信号特征融合方法,形成基于融合信号特征的旧油管腐蚀缺陷可视化手段。试验结果表明,相比传统脉冲涡流检测,所提方法得到的基于融合特征的腐蚀缺陷成像结果具有更高的图像信噪比;采用所提检测探头及信号特征融合方法,可对旧油管内壁缺陷实现高灵敏度、高信噪比的可视化检测。

管道包覆层材质对脉冲涡流检测影响的研究

管道的包覆层会影响脉冲涡流检测的信号。利用以有限元分析方法建立了塑料表皮、铁质表皮和铝质表皮3种不同材料包覆层的脉冲涡流检测模型。分析了3种材料的表皮涡流和管道涡流情况,计算了表皮与管道的电磁场能量。结果显示,塑料表皮上的电磁场能量最小,铝质表皮的涡流密度最大,铁质表皮上的电磁场能量较大。仿真结果显示,线圈电压与试验电压趋势一致。

脉冲涡流-电磁超声复合检测方法的可靠性评估

金属结构广泛应用于现代工业的各种领域,在其从生产、制造到服役各个阶段都有可能产生各类复杂缺陷。例如金属结构的表面和底部都出现复合缺陷的情况,单一的电磁无损检测方法难以满足所有需求。而使用两种或多种具有针对性的电磁无损检测方法进行检测,又存在检测效率低、成本高等问题。为解决这一难题,本文开发了一种新型的脉冲涡流-电磁超声一体化复合检测方法。该复合检测方法仅需使用一套检测系统和检测探头,基于同时解调出的电磁成分和超声成分,即可同步检测出金属结构的表面缺陷和底部缺陷,大大简化了实验系统,提高了复合缺陷的检测效率。此外,基于检出概率开发了一种可靠性评估方法,对脉冲涡流-电磁超声复合检测方法的检测能力进行评估。通过数值模拟和实验对脉冲涡流-电磁超声复合检测方法进行检出概率分析,以确定复合缺陷检测的最小可检尺寸。