【作者】 张勇；

【导师】 叶中付；

【作者基本信息】 中国科学技术大学 ， 信号与信息处理， 2007， 博士

【摘要】 无损检测是利用材料的某些物理量由于有缺陷而发生变化，测量其变化量，从而判断材料内部是否存在缺陷。无损检测是工业生产中实现质量控制、节约原材料、改进工艺和提高劳动生产率的重要手段，也是设备安全运行的重要监测手段。漏磁检测能对铁磁性材料提供快捷而相对廉价的检测。漏磁法因其对管材表面状态要求不高，检出深度也较大，而且可以发现材料内的多种不连续性，因而在许多工业领域中得到应用，是应用最广泛的无损检测技术之一。本文的主要研究工作有：首先，针对无缝钢管端部检测用的是磁粉检测方法，检测过程非自动化、检测结果很大程度上依赖于人的主观判断，以及检测效率低下这一现状，并结合无损检测朝着提高检测效率的发展趋势，提出了利用漏磁检测对无缝管端部进行检测的新方法。这个方法的特点是：设备结构上，对被检测钢管的端部增加一个引导钢管，这样增加了被检测钢管的长度，为漏磁检测提供了可能性；在漏磁信号处理上，引导管与被检测钢管不是一个整体，在两者接合处存在缝隙，这样由此缝隙产生的漏磁信号将严重干扰被检测钢管端部真正缺陷的漏磁信号，本文利用信号干扰抵消的方法来恢复缺陷漏磁信号。实验结果表明用漏磁法检测钢管端部是可行的，并能极大提高钢管端部检测的效率。其次，在漏磁检测中，受到传感器提离值、各传感器物理特性的差异、电子元器件差异等诸多因素影响，在相同检测条件下各通道输出的信号有较大的差异，这严重影响了检测设备的性能，并影响缺陷的评估。为消除这种影响，通常的方法是根据各通道的输出信号，人工手动的方式进行调整，这样造成操作效率不高、精度较低等缺点。本文提出了一种漏磁信道的均衡方法，选取一个信道的传输函数作为参考信道传输函数，用FIR滤波器来补偿其它信道的传输函数与参考信道传输函数的差异。实验结果表明这种方法具有良好的均衡效果和广泛的实际应用意义。然后，本文总结了磁偶极子应用在漏磁场分析中的研究成果，提出了一种利用漏磁信号分步重构缺陷形状的方法，并对半圆形、三角形、矩形这三种常见的缺陷形状举例进行说明。以上三个例子可以说明，本文提出的逐次逼近法重构缺陷的形状取得了较好的效果，与其它方法相比，有计算量小，重构方法简单的优点。在本文最后针对目前漏磁检测的研究现状，提出了进一步的研究方向。更多还原

【Abstract】 Based on the fact that some physic quantum would be changed because of existing defects, nondestructive testing (NDT) could detect the defects. NDT plays a important role of quality controlling and saving raw materials and improve productivity in industry manufacture. NDT is also a important inspection means for the equipment.As one of the most important, fastest and cheapest nondestructive testing methods, Magnetic flux leakage technology could be applied in inspection ferromagnetic materials. MFL is also the most commonly used in nondestructive testing and it could find the majority of discontinuities.The main research contents in this paper include:First, the undetectable area in seamless pipeline (pipeline heads) is usually inspected by magnetic particles, but magnetic particles merely inspect the defect near pipelines’ outer surface. The particle indication of defects is usually observed by eye, and so the testing reliability has a high human factor influence depending on the operator. For the reason of equipment itself, MFL inspection equipment couldn’t inspect the pipeline heads, which are regarded as an undetectable area in MFL examination. In this paper we attempt to use a new method based on MFL to inspect pipeline heads. We introduce the idea of leading pipeline, and expatiate the method of separating the MFL signal of defect near pipeline heads. The difference between reference signal and artificial flaw signal can be extracted properly by using correlation canceling. The experiments show that it is possible for MFL technology to inspect the tube head, and improve the inspection efficiency.Then, influenced by the lift-off value between the pipeline and coil sensors, the various properties of electronic component and the different location of coil sensor, the output signal’s amplitude and phase of each channel are different despite the same flaw in MFL inspection. The channel-to-channel mismatch may severely degrade the performance of testing equipment and disturb the evaluation of the level of flaw unless some form of compensation is employed. In this paper an adaptive method for channel equalization in MFL inspection is presented, we selected a channel as reference channel and used finite impulse response (FIR) filters to compensate the difference between the reference channel and other channels. Both theoretical analysis and experimental results have shown the effectiveness of the proposed method.And then, we summarized the development of the magnetic dipole, and proposed a method which be used to reconstruct the defect’s shape. We reconstructed the delta shape, semicircle and rectangle shape defects to illustrate the proposed method. Compared with the other methods, the reconstructed results have shown the merits of the proposed method.Finally, aiming at the research status quo in MFL inspection, we brought forward the new research directions.更多还原