磁导率扰动无损检测新方法及机理研究

The application of steel pipe, rail and other ferromagnetic structures is extensive in “the Belt and Road” strategy. However, the deeper defects of thick-walled steel pipe and solid rail are difficult to be inspected in the high-precision and high-efficiency conditions by traditional magnetic flux leakage testing which are restricted by the magnetic shielding effect and the magnetic compression effect. From the perspective of source transformation, this project studies the problems about the transmission of local permeability distortion information source caused by internal defects of the ferromagnetic materials. And a new nondestructive testing method measuring the permeability perturbation information on the metal surface is proposed. The nonlinear magnetization characteristic of ferromagnetic materials in the DC magnetization condition will be studied. The interaction mechanism between external magnetic field and the magnetization vector in the magnetic domain around defects will be clarified. Thus, the magnetic permeability perturbation characteristic caused by the internal layer defects because of the change of magnetic flux and its characterization method will be explored. On the basis of further analysis to the transmission mechanism of the material’s permeability distortion in the magnetization condition, the quantitative relationship of the defect morphology, the internal magnetic permeability distortion and the magnetic permeability distortion in surface layer will be acquired. The evaluation method based on the eddy current measurement of the permeability perturbation will be developed. The high-speed and high-precision inspection of thick-walled or solid structure’s internal deeper defects will be achieved. At last, a set of nondestructive testing theory system about magnetic permeability perturbation testing will be formed. Significant changes are expected to be brought to the new inspecting system for the buried pipeline and high-speed railway.

“一带一路”战略中应用广泛的钢管、铁轨等铁磁性构件的无损检测十分重要，但常规漏磁检测对厚壁钢管和实心铁轨的高效、高精检测受限于“磁屏蔽效应”和“磁压缩效应”难以实现更深层缺陷探伤。本项目从信源转化的角度，研究铁磁性材料内部缺陷产生的局部磁导率扰动信息源向外层的传递问题，提出在金属表面测量磁导率扰动信息的无损检测新方法。通过研究直流磁化下铁磁性材料非线性磁化特性，阐明外加磁化磁场与缺陷周围磁畴内部磁化强度矢量的相互作用机制，从而探索材料内部不同层次缺陷由磁通变动产生的磁导率扰动特性及其表征方法。在深入剖析磁化下材料磁导率畸变传递机制的基础上，获得缺陷形态、内部/表层磁导率畸变量及表面扰动电磁场之间的量化关系，建立基于电涡流测量表层磁导率扰动的评价方法，实现厚壁或实心铁磁性构件内部更深层缺陷的高速高精探伤，形成一套磁导率扰动无损检测新理论体系，有望为埋地管道、高铁的新一代检测装备带来重大改变。

漏磁检测广泛运用于钢管，铁轨等铁磁性构件的无损检测。针对常规漏磁检测下厚壁钢管和实心铁轨的高效、高精检测受限于“磁屏蔽效应”和“磁压缩效应”，难以实现更深层缺陷探伤的限制，本项目从信源转化的角度，研究铁磁性材料内部缺陷产生的局部磁导率扰动信息源向外层的传递问题，提出在金属表面测量磁导率扰动信息的无损检测新方法，为厚壁或实心铁磁性构件内部深层缺陷检测提供了检测技术支持。.本课题展开了以下五点研究：.a.在直流磁化中铁磁性材料的非线性磁特性的基础上，通过分析在μ-H曲线不同阶段位置，缺陷和磁导率空间分布的关联来建立缺陷磁导率扰动机理。使用解析模型和有限元计算模型获得不同埋深的缺陷磁导率扰动水平，以此探究磁导率扰动的表征方法，传递规律和影响因素。.b.基于“缺陷-磁导率扰动”的信源转化机制，研究了磁导率扰动无损检测(MPPT)新方法。采用等效磁导率法建立三维有限元模型，仿真结果表明，磁导率扰动对涡流分布产生影响，检测线圈能够拾取到感应信号。研究了一种高精度差分式MPPT探头，对探头差分间距、缺陷尺寸、探头提离及激励频率等影响因素进行了探究，实现了对钢板中埋深25mm缺陷的检测，突破了常规漏磁检测的探伤极限。.c.研究了MPPT方法检测信号中包括缺陷大小，磁导率扰动，漏磁场的多种信源的影响机制。为了分辨多源的影响关系，阐明了在不同的内、外部条件下，三者对信号的主导机制。随磁化器磁化电流的增加，内部和外部缺陷的信号幅度均呈现强烈的非单调变化。对于外部缺陷，漏磁场在大提离下的MPPT信号中占据主导作用；对于内部缺陷，磁导率扰动在深层缺陷的磁导率扰动检测信号中占据主导作用。以此阐明了多信源的作用机理。.d.基于MPPT方法的理论基础，分别展开了基于MPPT探头的表面缺陷大提离检测方法，分层缺陷测量方法，内外表面缺陷区分方法的研究，拓展了MPPT检测方法的应用体系。.e. 通过对比分析MPPT方法与常规漏磁检测、涡流检测方法的在厚壁小径钢管上的检测效果，阐明MPPT方法的优越性。研究了曲率半径对钢管表面漏磁场和表层磁导率扰动的影响，实验获得壁厚 12mm的Φ56mm钢管内壁0.6mm×25mm×0.5mm裂纹的检测信号，以此说明MPPT方法的工程应用价值。