Study on Novel Nondestructive Testing Strategies Based on MFL Change Rate and ACFM Principle

钢材具有强度高、成本低和加工性能良好等优点，是工业领域的重要原材料。但是，其不可避免会出现各种各样的缺陷，如裂纹、腐蚀坑和变形等，这些缺陷将给工程带来安全隐患，因此需要无损检测技术作为其最后一道保障措施，及时探测缺陷。对于大型的钢构件而言，如大面积平面钢板和长距离管道，漏磁检测技术是应用最广的无损检测手段，因为其操作简单，检测可靠性高，并且易于实现自动化，检测效率高。 本文针对漏磁检测长期存在的信号噪声问题，分析了噪声的特性和产生原因，将漏磁信号噪声分为背景噪声、扩散噪声和振动噪声，并提出以漏磁场强度的空间变化率作为检测指标的新检测方法。通过磁荷模型建立漏磁场空间变化率模型，从理论上论证了该...Steel is the one of the major materials widely used in most of the industry fields for its high strength, low cost and good processability. However, there inevitably appear some corrosion pits, cracks or grooves in the steel structure, which would lead to a potential engineering accident. Thus, the non-destructive testing, as the last line of the engineering safety, is required to detect various d...学位：工学硕士院系专业：航空航天学院_机械电子工程学号：1992014115288

New MFL detection method based on differential peak extraction using dual sensors

为了提高管道、储罐漏磁检测的准确度、灵敏度,同时抑制噪声干扰,提出了一种双传感器差分峰值侦测的漏磁检测新方法。首先,对实际漏磁检测过程存在的背景噪声进行分析,研究了检测器振动、磁隙变化、磁轭泄漏等噪声源的共模特性;其次,利用缺陷漏磁场的分布特点构造了一种新型的差分侦测结构,该结构既可对噪声进行共模抑制,又可实现缺陷特征信号的差模提取;再次,依托磁偶极子模型,对所提方法的机理进行了分析,并讨论实现该方法所需要的约束条件及其检测灵敏度特性;最后,开展了仿真和物理实验,实验结果表明,该方法的噪声仅为传统X分量检测的5%,Y分量检测的26%,且检测敏感度提高了2倍。该方法为优化漏磁检测器结构、提高检测的可靠性及灵敏性提供了一个新的思路。In order to improve the accuracy and sensitivity of pipeline and storage tank magnetic flux leakage( MFL) detection,as well as suppress noise interference,a new MFL detection method based on differential peak extraction using dual sensors is proposed. Firstly,the background noise in actual MFL detection process is analyzed and the common mode characteristics of the noise sources,such as sensor vibration,magnet gap change,magnet yoke leakage and etc. are studied. Next,a new differential detection structure is built based on the distribution characteristics of the defect magnetic flux leakage,which can restrain the common-mode noise and realize the differential extraction of the defect feature signal. Then,based on the magnetic dipole model the mechanism of the proposed method is analyzed,the restraint conditions required for realizing the new method and the detection sensitivity characteristic of the method are discussed. Finally,simulation and experiment study were conducted,and the results show that the noise with the new method is only 5%of the one with traditional X-component detection,and 26% with traditional Y-component detection. Moreover,the detection sensitivity is improved twice. The proposed method provides a new strategy for optimizing the MFL detection sensor structure,and improving the detection reliability and sensitivity.国家自然科学基金(51177141);; 航空基金(2012ZD68003)项目资

Novel MFL method for pipeline crack no blind spot detection using composite excitation

管道是石油和天然气工业的重要组成部分,而轴向裂纹是管道安全运营的重要隐患。传统的漏磁检测技术(MFL)对管道中轴向裂纹的检测灵敏度不高,从而形成检测盲区。本文提出了一种利用复合激励的MFL检测新方法,可实现对轴向和周向缺陷的同步检测。首先,利用U型磁轭对管壁进行交直流复合磁化;直流磁化场直接作用于周向裂纹并形成有效的MFL检测信号,而交流磁化场则在管壁内形成垂直于磁化方向的均匀涡流场;当该涡流场受到轴向裂纹干扰时,将形成二次感生磁场的扰动,因此,新方法通过对管壁表面的漏磁场及二次感生磁场检测,同时获得周向和轴向两个方向的探测能力;最后开展仿真和实验,并分析了新方法中作用于轴向和周向裂纹的磁化场、涡流场和二次感生磁场的分布。结果表明,新方法只需通过一次扫描,即可以获得缺陷的轴向和周向特征,实现了对裂纹的无盲点检测。Pipelines are the critical components in oil and gas industry,axial cracks caused by stress corrosion and fatigue damage are the hidden danger of pipeline safe operation. The conventional magnetic flux leakage( MFL) detection technique is inadequate for accurately detecting the narrow axial crack in pipeline and forms detection blind region. In this paper,a new MFL detection method capable of simultaneously detecting both axial and circumferential defects is proposed utilizing DC-AC composite excitation. Firstly,the measured pipe wall is magnetized by DC-AC compound magnetic field using a U-shaped yoke. The DC magnetic field is directly acted on the circumferential crack and generates effective MFL detection signal. The AC magnetic field generates a uniform eddy current field perpendicular to the magnetization direction inside the pipe wall. When the eddy current field is disturbed by the axial crack,a secondary induced magnetic field is generated. Through detecting the surface magnetic flux leakage and secondary induced magnetic field,the new method can obtain the axial and circumferential crack detection capability simultaneously. Both simulations and experiments were conducted,the distributions of the magnetizing field,eddy current field and secondary induced magnetic field acting on the axial and circumferential cracks were analyzed. The results show that the proposed new method can detect both axial and circumferential cracks effectively with one pass scanning,the pipeline crack no blind spot detection is achieved.国家自然科学基金(51177141,51677158);; 航空基金(2012ZD68003)项目资

New NDT method for ferromagnetic materials based on differential permeability

利用微分磁导率变化特性,提出了一种可对材料的宏观缺陷进行快速扫查的无损检测新方法。首先,将铁磁性材料置于偏置磁化场环境下,缺陷将导致内部磁通的畸; 变;其次,磁通畸变进一步体现在材料表面微分磁导率分布的差异性;再次,通过特殊设计的微分磁导率检测探头,对材料表面微分磁导率的分布进行扫查;最后,; 由磁导率分布差异获得材料内部的不连续性信息,从而实现对缺陷的无损检测。开展了系列验证实验,结果表明,相对于传统的漏磁检测方法,新方法具有磁化强度; 低、磁通泄漏少、检测信号稳定的特点。新方法正、反面缺陷探测信号存在差异,在缺陷深度识别方面亦存在优势。A new non-destructive testing method is proposed to fast scan and detect; the macroscopic defects of materials using the variation characteristics; of the differential permeability of ferromagnetic materials. Firstly,the; ferromagnetic material,such as steel plate,is placed under the bias; magnetic field,and the defects in the material will inevitably lead to; the distortion of its internal magnetic flux. Secondly,the magnetic flux; distortion is further reflected in the difference of the differential; permeability distribution on the surface of the tested material.; Thirdly,using a specially designed probe,the distribution of; differential permeability on the surface of tested material is rapidly; scanned. Finally,from the difference of the differential permeability; distribution,the discontinuity information in the material can be; obtained,so as to realize the nondestructive testing of macroscopic; defects. Series of experiments were carried out,and the results show; that,compared with traditional magnetic flux leakage method,the new; method has the advantages of low magnetic intensity,less flux leakage; and stable detection signals. Moreover,the detection signals for the; front-side and back-side defects have obviously different distribution; characteristics,and the method also has obvious advantages in the field; of defect depth identification.国家自然科学基金; 福建省科技计划重大专

一种带有误差补偿项的折线线圈阻抗解析建模新方法

提出一种包含误差补偿项的任意折线线圈阻抗解析新模型。首先,在前人研究的基础上,通过定义外形位置因子,简化单矩形折线线圈的阻抗计算。其次,对多个单矩形折线线圈之间的相交耦合作用进行研究,建立串联等效电感模型。再次,讨论任意形状折线线圈的拆解和重构过程,研究重构过程的误差分布,并推导出误差补偿的数学表达;进而得到任意形状折线线圈的入射场阻抗及散射场阻抗的完整解析模型。最后,对螺线形折线线圈这一典型特例进行计算,绘制阻抗平面图,并利用高精度阻抗测试仪进行物理验证实验。结果表明,所提方法能有效补偿线宽因素带来的误差,可对置于导体上方的具有不同激励频率和提离的任意形状折线线圈的阻抗进行解析计算。国家自然科学基金(51177141);;航空基金(2012ZD68003

Mechanism analysis of influence of surface-breaking orientation on magnetic leakage field distribution

由于漏磁检测(MFL)具有操作简单、成本低廉、信号稳定等特点,已被广泛应用于铁磁材料的无损检测.在MFL领域,实现缺陷评估的关键是对漏磁信号与缺; 陷几何特征之间的关系进行准确描述.本文建立了一个任意方向的表面缺陷漏磁场分布的三维数学模型.首先,将表面缺陷近似为一个有限长的矩形槽来进行描述;; 然后,从理论上分析了不同缺陷方向下槽壁磁荷密度的变化规律;最后,通过矢量合成得到了有向缺陷的漏磁场分布.开展了仿真和实验,对缺陷在不同磁化方向下; 的漏磁场分布进行了分析.实验结果表明,缺陷的MFL分布与方向性密切相关.随着与磁化方向夹角增大,缺陷漏磁场水平分量亦增加,单峰性也越突出;但垂直; 分量却随夹角的增大而呈现双峰分布.所建模型能有效地描述缺陷的方向性对漏磁场分布影响,对优化MFL检测器设计和提高缺陷评估质量有实际指导意义.Magnetic flux leakage (MFL) has been widely applied to the nondestructive testing (NDT) of ferromagnetic materials due to its simple operation, low cost, and steady signal. Its defects are evaluated based on the relationship between MFL signal and the geometrical characteristic of defect. In this paper, a three-dimensional (3D) mathematical model is developed for the magnetic leakage field of surface- breaking defects that are arbitrarily oriented inside ferromagnetic material. Firstly, a finite-length rectangular slot is used as a simplified and convenient representation of a surface-breaking defect. Then, the magnetic charge densities of slot walls in different surface-breaking orientations are analyzed theoretically. The distribution of the magnetic leakage field can ultimately be derived by vector synthesis. Both simulations and experiments are conducted to analyze the magnetic leakage field distributions in different magnetization orientations. The results show that with increasing the angle between the defect orientation and the magnetic field, the horizontal component of the leakage magnetic field increases as demonstrated by increasing the prominence of its single peak. At the same time, however, the vertical component shows a bimodal distribution. The proposed model can effectively describe the influence of defect orientation on MFL signals, which can offer practical guidelines for optimizing MFL detectors and improving defect assessment.National Natural Science Foundation of China [51177141, 51677158