Liu Wenlong, Ren Lemei, Tian Guansan
School of Thermal Engineering, Shandong Jianzhu University, Jinan 250100, China.
Sensors (Basel). 2024 Aug 11;24(16):5195. doi: 10.3390/s24165195.
Magnetic flux leakage (MFL) inspection employs leakage magnetic fields to effectively detect and locate pipeline defects. The spacing between magnetic poles significantly affects the leakage magnetic field strength. While most detectors typically opt for moderate pole spacing for routine detection, this study investigates the propagation characteristics of MFL signals at small pole spacings (under specimen oversaturated magnetization) and their impact on MFL detection. Through finite element simulation and experiments, it reveals a new signal phenomenon in the radial MFL signal at small pole spacings, the double peak-valley (DPV) phenomenon, characterized by outer and inner peaks and valleys. Theoretical analysis based on the simulation results elucidates the mechanisms for this DPV phenomenon. Based on this, the impact of defect size, pipe wall thickness, and magnetic pole and rigid brush height on MFL signals under small magnetic pole spacings is examined. It is demonstrated that, under a smaller magnetic pole spacing, a potent background magnetic field manifests in the air above the defect. This DPV phenomenon is generated by the magnetic diffusion and compression interactions between the background and defect leakage magnetic fields. Notably, the intensity of the background magnetic field can be mitigated by reducing the height of the rigid brush. In contrast, the pipe wall thickness and magnetic pole height exhibit a negligible influence on the DPV phenomenon. The emergence of the DPV precipitates a reduction in the peak-to-valley difference within the MFL signal, constricting the depth range of detectable defects. However, the presence of DPV increases the identification of defects with smaller opening sizes. These findings reveal the characterization of the MFL signal under small pole spacing, offering a preliminary study on identifying specific defects using unconventional signals. This study provides valuable guidance for MFL detection.
漏磁检测（MFL）利用漏磁场来有效地检测和定位管道缺陷。磁极间距会显著影响漏磁场强度。虽然大多数探测器在常规检测时通常选择适中的磁极间距，但本研究调查了在小磁极间距（在试样过饱和磁化情况下）时MFL信号的传播特性及其对MFL检测的影响。通过有限元模拟和实验，揭示了在小磁极间距下径向MFL信号中的一种新信号现象，即双峰谷（DPV）现象，其特征为外部和内部的峰与谷。基于模拟结果的理论分析阐明了这种DPV现象的机制。在此基础上，研究了在小磁极间距下缺陷尺寸、管壁厚度以及磁极和刚性刷高度对MFL信号的影响。结果表明，在较小的磁极间距下，缺陷上方空气中会出现强大的背景磁场。这种DPV现象是由背景磁场和缺陷漏磁场之间的磁扩散和压缩相互作用产生的。值得注意的是，通过降低刚性刷的高度可以减弱背景磁场的强度。相比之下，管壁厚度和磁极高度对DPV现象的影响可忽略不计。DPV的出现导致MFL信号内的峰谷差减小，限制了可检测缺陷的深度范围。然而，DPV的存在增加了对较小开口尺寸缺陷的识别能力。这些发现揭示了小磁极间距下MFL信号特征，为利用非常规信号识别特定缺陷提供了初步研究。本研究为MFL检测提供了有价值的指导。
