非饱和磁化下钢管缺陷涡流检测的定量评价方法研究

The standard about the eddy current testing of steel pipes such as ASTM E309-2011 regards that after magnetic saturation, steel pipes can be considered as non ferromagnetic pipes, the inspection results have no relation with pipe magnetic properties. However, this point ignores the effect of pipe defect magnetic properties and leakage magnetic field, which leads to the detection mechanism imperfect, making the distortion of quantitative evaluation about defecting. This project is to research eddy current testing of steel pipe magnetic properties affecting theory and quantitative evaluation about defecting. By knowing unsaturation properties of steel pipe defecting magnetic properties and leakage magnetic field under magnetic saturation, it also researches the magnetic properties in defecting areas and the effect between magnetic field and response signal, revealing the theory of eddy current testing of effect about steel pipe magnetic properties. And we propose the improved algorithm of equivalent magnetic permeability, which achieves the harmonic model about eddy current testing of steel pipe under the different magnetic method and exciting magnetic intensity. Thus, we research the particular defecting in different positions and the identification method of parameters. We study the signal disturbance theory of steel pipe and the optimization of testing models under high speed inspection, and then construct effective inversion optimization defecting model, which achieves the quantitative evaluation theory and method of defecting.. This project is of significance on the research and engineering application value to the nondestructive evaluation and reliability analysis of steel pipes. The result can be used in the security maintenance of ferromagnetic items in areas such as mechanics,special equipment,petrochemical industry, and so on.

钢管涡流检测相关标准如ASTM E309-2011认为，钢管饱和磁化后相当于非铁磁性管道，探伤结果与管道磁特性无关，这种观点忽视了此时缺陷磁特性和漏磁场参量的影响，使得缺陷量化评价失真。本项目旨在研究钢管涡流检测的磁特性影响机理及缺陷量化评价方法。通过掌握磁饱和下钢管缺陷磁导率非均匀特性和漏磁场分布，研究这两个参量与响应信号之间的作用规律，揭示钢管饱和磁化时磁特性影响的涡流检测机理；提出磁导率等效处理的改进算法，实现不同磁化方法和励磁强度下钢管涡流检测模型的时谐稳态计算，结合实验手段研究非饱和磁化下典型缺陷不同层次位置和参数的辨识方法；研究非饱和磁化下钢管高速探伤时信号扰动机理及模型优化，建立高效的缺陷反演模型，提出钢管缺陷的涡流检测定量评价理论和方法。.本项目对钢管的无损评价具有重要的理论研究意义和工程应用价值，研究成果可应用于机械、特种设备和石油化工等领域铁磁构件的安全维护。

基于磁饱和技术的涡流检测法广泛应用于钢管的缺陷评估，在工程界已实践多年，研究人员总结规律并形成了多项国家标准，但机理认识一直不完善，导致缺陷评估失真。目前对钢管的品质提出了更高的要求，因此开展钢管涡流检测法机理和缺陷量化评价方法的研究既具有重要的理论研究意义，同时对工程实践也极具应用指导价值。. 以Dodd-Deeds模型为基础，以球形磁畴的畴壁可逆与不可逆位移分别表征交流和直流磁化的作用贡献，获得强磁化下钢管的磁导率变化。考虑强磁化后缺陷区域电磁特性的变化，建立钢管涡流检测的积分解析模型，提出了钢管强磁化下涡流检测的磁特性影响的物理机理，为缺陷的量化评价奠定了理论基础。. 进一步通过仿真计算和试验测试两方面论证缺陷漏磁场对穿过式涡流探头的作用贡献。扰动磁源的空间畸变磁场产生的低频响应叠加在涡流探头的交变激励信号中，形成了以低频信号为基波而高频信号为调制波的调幅波信号，经相敏检波后其作用消除，进而澄清了缺陷漏磁场的贡献。. 以钢管为研究对象，发现磁饱和下钢管内外壁缺陷区域的磁特性并非为均匀特性，这与常规观点认识不同；提出了一种磁导率等效处理的算法，解决了谐波法不能同时加载交、直流激励的难题，开展了考虑磁特性影响的厚壁钢管磁饱和下涡流检测仿真和试验研究，剖析了磁饱和下钢管磁特性影响的涡流检测机理。.提出了评价材料电导率、磁导率的新型传感器及评价方法，设计了阵列涡流传感器、U型磁轭式涡流传感器，研制了信号激发、功率放大电路、信号调理电路，研究了电导率、磁导率的测试方法和影响因素，优化了传感器和测试方法。. 针对钢管涡流检测采用磁饱和法评价的不足，提出了一种在非饱和磁化区辨识不同层次位置和参数缺陷的涡流检测方法，研究了区别于磁饱和状态时的内、外伤信号的幅值和相位变化特征，并进一步开展了检测机理探讨。为进一步优化涡流检测方法，提出了内、外伤辨识的方法，为缺陷量化评价提供理论与技术支撑。