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。     

涡流检测缺陷定量评估的研究

在涡流检测中实现缺陷定量评估具有重要意义。通常涡流检测是利用线圈阻抗变化来实现缺陷检测,分析受缺陷扰动的磁场量B的分布变化,比传统的涡流检测方法更有利于实现缺陷定量评估。利用有限元方法,对有裂纹的金属平板的空间磁场进行了数值仿真。仿真结果证实可通过分析磁场量B的变化来实现缺陷定量评估,并得到了缺陷的长度、深度与平板表面的磁场分量之间的量值关系。对平板裂纹的定量评估提供了理论上的依据。     

油气长输管道管体损伤的高速涡流磁场检测

针对油气长输管道外壁缺陷影响管道安全运行的问题，提出了一种基于动生涡流磁场的无损检测方法。借助ANSYS Electronics有限元分析软件分析了管道表面缺陷参数、检测速度与动生涡流磁场之间的关系，发现在不同管道表面缺陷参数下，动生涡流磁场会根据缺陷形状、尺寸的差异反馈出不同的磁感应强度信号，缺陷尺寸越大，信号反馈越强烈；随着检测速度的提高，动生涡流的磁感应强度逐渐增大，但整体变化趋势基本一致。根据工程实际研制了基于动生涡流磁场的管道无损检测试验装置，开展了试验研究，得到了与仿真相同的规律性结果，从而验证了该技术的可行性，表明动生涡流磁场无损检测方法能够对管道缺陷进行精准定位与辨别。     

交变磁场测量的缺陷识别模型

交变磁场测量方法由于其无需标定、对表面要求不高、具有完善的数学模型和可实现缺陷定量分析等特点，正越来越受到无损检测界人士的关注。通过对其原理的分析介绍，在利用基于正交型锁相放大器(LIA)的三维磁场微弱信号测量系统对缺陷磁场进行数据采集的基础上，提出了基于缺陷环幅值斜率比值的两种缺陷识别模型，并对其判断规则和结果进行了分析。     

金属亚表面腐蚀缺陷的脉冲调制涡流磁场梯度成像

由于工况复杂,在役金属构件极易产生亚表面腐蚀缺陷,严重影响其安全运行。脉冲调制涡流检测技术是一种新型脉冲涡流检测技术。相较传统脉冲涡流检测技术,其在金属构件缺陷检测和评估中具有优势;将其与磁场梯度测量技术有效结合,探究其在金属构件亚表面腐蚀缺陷检测中的成像方法和技术优势。通过有限元分析,发现相较脉冲涡流磁场梯度信号,脉冲调制涡流磁场梯度信号对金属亚表面腐蚀缺陷边缘识别具有更高的灵敏度。并且,搭建了相关试验系统,通过试验验证了仿真分析结论。试验结果表明,脉冲调制涡流磁场梯度检测信号对金属构件亚表面腐蚀缺陷成像具有更高的精度,有利于缺陷的检测。     

有限元方法在管道外漏磁检测中的应用

管道漏磁检测及其缺陷漏磁场的仿真技术研究具有十分重要的意义。在对各种漏磁场计算方法进行比较之后,选择了有限元法作为主要研究工具。叙述了漏磁检测的基本原理,介绍了漏磁管道检测装置的工作原理和基本结构,建立了管道漏磁检测中缺陷漏磁场计算的三维有限元模型,并以此为基础分别研究了缺陷漏磁信号特点、缺陷的几何尺寸与漏磁信号的关系、以及材料壁厚等对漏磁信号的影响等问题。通过对多磁化单元结构进行有限元模拟和试验仿真,发现多个磁化单元会造成磁场的叠加,磁化单元数量的增加会使缺陷处漏磁场增强,并且中间磁化单位的增加量要大于两侧。缺陷的几何尺寸影响漏磁场的分布,在一定缺陷直径范围内,缺陷深度与漏磁场信号强度呈近似线性关系。无论被测管道壁厚如何变化,相同几何参数的缺陷漏磁场轴向分量变化趋势仍然相同。适当选取提离值,将有助于获得良好的漏磁场信号。     

扰动磁场检测技术中裂纹磁场信号的反演

依据试验数据和有限元仿真结果,分析了裂纹缺陷特征与扰动磁场分布的关系,总结出交流场检测技术中磁信号裂纹尺寸反演的基本规律。借助于B_x扰动磁场信号形状与裂纹缺陷特征之间的相似性,建立了二维表面缺陷形状的反演算法。     

漏磁二维检测的试验研究

传统的漏磁检测是经磁化后测量试样表面漏磁场的垂直分量再对拾取的信号量进行分析研究的方法,然而这种仅通过单一垂直分量特性来判定缺陷的方法易出现漏检、误判。针对该方法的不足,本研究采用了一种在测量漏磁场垂直分量的同时又提取并分析水平分量特性的二维检测方法,考虑到水平分量易受干扰信号影响,运用了矢量合成法提取水平分量,通过联合利用漏磁场的垂直分量存在过零点和水平分量具有最大值特性的方法来判断缺陷,并选取多种标准与自然试样进行试验研究。试验结果表明：采用漏磁二维检测可有效实施铁磁构件的缺陷检测,提高检测可靠性,可望有很好的实际工程应用前景。     

脉冲漏磁传感器的优化设计与试验验证

在铁磁性板材、管道腐蚀、裂纹等缺陷检测方面,脉冲漏磁技术显示了潜在的优势。在对多种不同结构的传感器进行仿真分析的基础上,提出了一种新型励磁结构的脉冲漏磁传感器,减少了背景噪声磁场对缺陷漏磁信号的磁场压缩作用,提高了传感器对缺陷信息获取的准确性,适合于绝缘层或涂覆层下缺陷的检测。研制了新型传感器,并对标准试件进行了测试。试验证明了传感器设计的正确性及有效性。     

6063铝合金表面缺陷交流电磁场检测

利用交流电磁场技术对铝合金试件缺陷进行检测.在模拟的人工表面缺陷上覆盖非导电涂层,研究6063铝合金试件表面缺陷在不同厚度覆盖层下的检测结果.针对特定缺陷,每次扫查后,通过观察Bx曲线图和Bz曲线图,确定在当前缺陷深度下,交流电磁场检测能够穿透最大的覆盖层厚度;针对不同深度缺陷,在0.42 mm至5 mm覆盖层范围内,...     

Method for sizing of 3-D surface breaking flaws by leakage flux

A method is proposed for sizing of 3-D surface breaking flaws with complex profiles. The method can be used for either magnetic materials or conductive materials when a magnetic field or electric current are distributed homogeneously inside the sample. The distribution of the intensity of the leakage magnetic field or electric field has to be measured at a constant distance above the surface of the sample in a direction perpendicular to the long axis of the flaw. The method is based on a dipole model of the flaw which predicts the intensity of the leakage field and on minimisation of the error between the measured distribution of the intensity of the leakage field and the corresponding theoretical distribution which changes with the size of the flaw. Computations are made for sizing of flaws with different shapes and sizes while it is assumed that the density of the charge at the walls of the flaw can vary. It is shown that the method allows fast distinguishing of the shape of a particular flaw where the sample contains several flaws with different shapes and the sizes of these flaws are known. Fast determination of the size of a particular flaw is achieved when the sample contains flaws with the same shape and different but known sizes. Also, the size of the flaw and the density of the charge at the walls of the flaw could be computed precisely, independently of the initial approximation of the minimisation procedure, when the shape of the flaw is known. The speed of the minimisation process increases with the decrease of the measurement distance from the surface of the flaw. Experimental requirements for precise flaw sizing are discussed.     

Eddy current flaw characterization in tubes by neural networks and finite element modeling

For quantitative flaw characterization in steam generator tubes, inversion of eddy current testing (ECT) signals in an automated fashion is strongly desired. In this paper, we report our effort to develop a systematic approach for flaw characterization in tubes by the novel combination of neural networks and finite element modeling.Specifically, the finite element model that can predict ECT signals from axisymmetric flaws in tubes was developed, and its accuracy was verified experimentally. Using this model, an abundant synthetic database with 400 ECT signals generated from 200 axisymmetric machined grooves in four types has been constructed with two test frequencies per flaw.For the automated inversion of ECT signals, a total of 22 features have been extracted from each flaw. Then, a set of 10 features has been selected for flaw classification, while the other set of 10 features for flaw sizing. For the determination of the flaw type and the flaw size parameters, we have proposed an intelligent flaw characterization system that adopts two different paradigms of neural networks: probabilistic neural networks for flaw classification and back propagation neural networks for flaw sizing.The performance of this system has been investigated using the synthetic ECT signals in the database. The excellent performance presented here, even though it has been obtained from synthetic flaws representing machined grooves in tubes, demonstrates the high potential of this system to serve as a robust tool for practical flaw characterization in tubes.     

矩形缺陷的交变漏磁检测信号分析方法

利用ANSYS仿真软件，首先对交变漏磁检测中影响矩形缺陷信号的各项因素进行了分析，并以此为基础，提出了以矩形缺陷为基本单元的信号分析方法。利用该方法分析了截面为梯形和圆形，及其它任意形状的直线裂纹的检测信号特点，同时也分析了圆弧形裂纹以及其他任意形状的非直线裂纹的检测信号特点，并对上述不同类型缺陷的识别进行了详细的论述。     

传热管内相位大于40°的缺陷信号分析

在核电站凝汽器钛管涡流检测中，发现部分内伤在辅频通道上的信号相位大于40°，不符合内伤信号的规律。针对这类信号显示进行分析研究，通过试验发现此类信号为内壁轴向缺陷的显示特征。另外，应对传统判伤曲线进行修正，提高内伤定量精度。     

交变漏磁检测中螺纹不同缺陷位置的识别方法研究

依据缺陷在螺纹区域的不同位置，将缺陷分为三类，分析了每类缺陷检测信号的特点，提出了识别判据，最后通过对膨胀螺钉上的该三类缺陷的检测，验证了识别模型的正确性。另外，对六角头螺栓结构根部缺陷的检测进行了试验研究，利用测量信号完成了缺陷的检测。     

基于超声信号和图像融合的焊缝缺陷识别

超声无损检测已被广泛用来检测材料内部的缺陷,然而对缺陷性质的识别始终是检测的难点,为此研究了一种基于超声信号和图像融合的焊缝缺陷识别新方法.该方法充分利用检测数据,通过对缺陷回波信号特征与缺陷形态特征的数据融合,实现了焊缝缺陷的有效识别.利用自主研制的超声成像手动检测系统对含有气孔、夹渣、裂纹、未焊透和未熔合五类典型焊接缺陷的焊件进行了检测,分别提取缺陷的超声回波信号特征和缺陷图像的形态特征,构建神经网络实现超声信号和图像特征的数据融合.结果表明,该方法实现了多类缺陷的识别,提高了缺陷识别率,有助于焊缝质量评定.     

基于PC机的多通道超声波探伤系统

根据超声波脉冲反射法基本原理,设计了以C8051单片机为控制核心、采用PCI8001高速采集卡进行数据采集的四通道超声波探伤系统平台。为了实现对缺陷的有效评估,采用VC6．0开发了超声波检测信号分析系统,实现了对超声波波形的实时数据采集、显示和缺陷的自动报警。试验结果表明,该系统有着较广泛的适用性。     

Evaluation of echo features of ultrasonic flaws and its intelligent pattern recognition

In this paper, three types of weld flaw were taken as target, evaluation and recognition of flaw echo features were studied. On the basis of experimental study and theoretical analysis, 26 features have been extracted from each echo samples.A method which is based on the statistical hypothesis testing and used for feature evaluation and optimum subset selection was explored Thus. the dimensionality reduction of feature space was brought out, and simultaneously, the amount of calculation was decreased. An intelligent pattern classifier with B-P type neural network was constructed which was characterized by high speed and accuracy for learning. Using a half of total samples as training set and others as testing set, the learning efficiency and the classification ability of network model were studied. The results of experiment showed that the learning rate of different training samples was about 100％. The results of recognition was satisfactory when the optimum feature subset was taken as the sample's feat     

管道焊缝未熔合的底片评定

对管道焊缝射线照相底片进行评定时,由于焊缝存在的单边未焊透、条形缺陷、根部内凹和咬边及成型不良等影像类似未熔合,而引发各方对缺陷定性的争议。就管道焊缝和射线照相工艺特点,研究未熔合和相类似缺陷的影像特征及评定方法,以帮助正确判定未熔合。     

石油管道的高速检测与缺陷识别

漏磁探伤法结合磁通量检测法可检出管全内、外壁及内部各种缺陷,描述检测图形曲线。通过长期检测数据积累,将有缺陷的和经过解剖对比的石油管道图形曲线资料输入计算机作为缺陷类型模板。检测中由计算机分析缺陷信号,与反比较,识别、分选出对油井有严重危害的管道。