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.

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。

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。

表贴式永磁电机在PWM激励下永磁体涡流损耗计算模型

针对现有模型难以计算PWM激励下表贴式永磁电机永磁体涡流损耗问题,提出了一种计算由PWM谐波引起的永磁体内涡流损耗计算模型。该模型通过磁导率分布函数获取气隙径向磁密,能够考虑定子开槽及谐波电流影响。首先,在忽略涡流反作用情况下解析计算了永磁体内磁密变化率;然后,应用有限差分法数值计算了永磁体内电位,综合得到了涡流损耗;最后,用有限元法验证了模型的准确性。研究结果表明:随着永磁体分段数的增大,涡流损耗减小,涡流反作用也随之减弱;永磁体涡流损耗主要由1倍、2倍开关频率附近电流谐波引起。

线圈放置方式对脉冲涡流检测的影响分析

[目的]核电厂汽水管线一般在管道外壁加装保温层,从而提高换热效率。目前对于铁磁性管道的检测手段主要为常规超声及超声导波,检测前需要将管道外壁保温层拆除,导致检测工期延长,人力成本增加,无法达到核电厂高质量发展的要求。核电厂脉冲涡流技术的应用可以省去保温层的拆装,实现不停机在线筛查。检测线圈的放置方式对缺陷的检出能力是脉冲涡流技术重要指标。[方法]文章利用ANSYS中的Maxwell模块进行管件建模及仿真,分别设计同轴式与垂直式检测线圈,保持提离距离、材料一致及其他条件一致下,模拟脉冲涡流对平底缺陷的检测能力。选取核电厂样管进行同轴式与垂直式脉冲涡流测试,将脉冲涡流(Pulsed Eddy Current Testing,PECT)测试结果与超声测厚进行复核,对比两种线圈放置方式对脉冲涡流检测的影响。[结果]研究表明:垂直式线圈相对于同轴式线圈对缺陷检出效果更佳。[结论]核电厂脉冲涡流技术的应用对脉冲涡流技术在核电领域实施具有重要意义。

脉冲涡流检测在核电厂管道的应用

[目的]为了提高换热效率,核电厂的凝结水管线、主给水管线、疏水管线及部分抽气管线管道外侧均加装了包覆层,目前对于铁磁性管道的检测手段主要为常规超声技术及超声导波技术。上述检测技术受限于检测环境及前提条件,检测难度较大。文章旨在提高带保温层管道的检测效率,丰富技术手段,缩短检修工期,提高核电厂经济效益。[方法]通过研究核电站低频电磁干扰下脉冲涡流检测方法的可行性和可靠性,利用感应电压测量值与计算值建立最优化参数反演问题,并结合参数之间的耦合关系式,根据管道脉冲涡流场时域解析解的基础上,建立感应电压测量值与计算值特定关系式,建立最优化参数反演问题,并结合参数之间的耦合关系式,提出1种针对核电厂带保温管道在役运维的脉冲涡流检测技术。[结果]利用文章提出的铁磁管道相对壁厚脉冲涡流检测方法对核电厂在役样管进行检测,并将检测结果与常规超声检测结果进行对比,得出二者检测结果误差在5%左右。[结论]脉冲涡流检测结果可靠,适用于核电厂铁磁管道壁厚腐蚀减薄的无损检测与评估。

基于刀片式激励线圈旋转的脉冲涡流探头

脉冲涡流检测裂纹时,微裂纹在感应涡流中产生的扰动微弱,检测信号的信噪比低;另一方面,单向扫查下的常规脉冲涡流探头难以获得多向裂纹检测的最大灵敏度和判断裂纹方向。提出一种采用机电旋转脉冲涡流激励线圈的检测方法,实现了多方向微裂纹的高灵敏度检测。刀片式激励线圈具有明显的聚磁性与方向性,机电旋转激励线圈后可以获得不同转角下的接收信号,将该接收信号与基准信号进行差分,提取出微小的峰值变化量,得到角度与峰值变化量之间的图谱。试验验证与测试结果表明:基于刀片式激励线圈在空心接收线圈内旋转的脉冲涡流探头不仅具有亚毫米级裂纹深度区分的检测能力,且能有效分辨裂纹方向,误差为±5°。

脉冲涡流检测频域提离交叉点的测厚研究

针对时域LOI在铁磁性和非铁磁性材料的脉冲涡流检测信号中的获取方法不统一问题,并致使时域LOI信号特征的提取标准统一性受到限制.文章通过分析铁磁性和非铁磁性材料的脉冲涡流差分信号,研究探头提离变化对脉冲涡流差分信号幅值谱、相位谱、实部谱的影响规律,获取脉冲涡流差分信号频谱中的频域LOI,并进一步分析频域LOI的厚度测量的可行性,为统一和扩展LOI的获取方法及改善LOI的测量范围提供方法指导.

用于镀锌铁皮保护层下检测的脉冲涡流技术研究

在实际应用中,脉冲涡流检测技术会受到保温层外的保护层的影响,其中镀锌铁皮保护层对脉冲涡流信号影响较大。研究了不同保护层对脉冲涡流信号的影响,重点分析了镀锌铁皮厚度、提离高度和镀锌铁皮振动对脉冲涡流信号的影响,并提出了解决方案:当提离高度相同时,带镀锌铁皮保护层的脉冲涡流信号幅值较不带保护层时的信号幅值大幅减小,此时需选择穿透能力更强的检测探头并提高发射电流强度;当以晚期信号斜率作为表征壁厚的特征值时,提离高度对计算壁厚的影响较小;考虑到磁致伸缩引起的探头振动,检测过程中应避免检测探头与镀锌铁皮直接接触。

LNG管道在线检测技术现场应用研究

针对液化天然气(LNG)管道在线检测,采用红外热成像、脉冲涡流、数字射线成像(DR)、电磁超声测厚等检测技术,对LNG管道进行了现场验证测试,并对各技术现场检测存在的主要问题进行分析,提出相关的建议。对目前LNG管道在线检测法规标准方面存在的问题进行了讨论,提出了制定和完善LNG管道在线检测相关法规标准的建议。

脉冲涡流检测激励电源设计

脉冲涡流检测是当前金属材料无损检测主要的方法,激励电源作为系统中的关键部分,其性能将直接影响到检测结果。针对现有材料缺陷脉冲涡流检测方法中激励电源存在关断时间长、无恒流控制、功率小等问题,对非磁性材料的缺陷检测方法进行了研究,提出了一种新的脉冲电源电路,采用线性调整型恒流源,实现恒流与恒压钳位的复合电路拓扑结构。首先对线性单元进行闭环分析,证明了电路的可行性,再通过样机实证,验证了脉冲电源的稳定性和快速性。脉冲电源的幅值在20 A内可调,幅度误差小于1%,能够快速关断,下降时间可达纳秒级。最后利用该脉冲电源组成了一套脉冲涡流检测系统,并对铝合金进行了裂纹缺陷模拟检测实验。通过提取探测器峰值电压发现系统能够准确地识别不同缺陷深度,且具有较高的分辨率。

脉冲涡流C扫描技术在储罐腐蚀检测中的应用

某储罐服役17年后,拆开保温层后发现罐壁发生大面积腐蚀,常规腐蚀测厚技术无法开展腐蚀检测工作。本文采用搭载脉冲涡流探头的爬行机器人开展储罐C扫描壁厚测量,成功获得储罐的壁厚腐蚀减薄情况。结果表明储罐壁厚减薄程度未超过腐蚀裕度,开展防腐维修后可继续使用。

某油田分公司储水罐脉冲涡流腐蚀检测与分析

通过对某油田腐蚀分析,发现该油田的主要腐蚀因素是氯离子、溶解氧以及硫酸盐还原菌。通过对以往腐蚀挂片数据统计分析,腐蚀属于极严重程度等级,结合腐蚀分析以及相关标准,对2#储水罐进行脉冲涡流腐蚀检测,发现2#储水罐腐蚀非常严重,对2#储水罐腐蚀缺陷进行等级划分,并提出相关建议。