【作者】 任海燕；

【导师】 丁克勤； 梁丽红；

【作者基本信息】 中北大学 ， 信号与信息处理， 2009， 硕士

【摘要】 水冷壁管是电站锅炉内部的主要构件,对其腐蚀缺陷的在线检测具有巨大的经济价值。低频涡流检测技术对管道内表面的缺陷具有较高的灵敏度,有着很好的应用前景。为了进一步了解该技术,使之更有效的应用于水冷壁管内壁腐蚀缺陷的检测,本文利用有限元分析软件ANSYS对低频涡流检测进行仿真研究,得出的结论将为实际的探头设计及检测提供理论依据。文章首先根据电磁感应原理对低频涡流检测的工作原理进行介绍,接着通过麦克斯韦方程组了解感应磁场和涡流在被测试件中传播的规律,得出检测试件的内表面缺陷时需要选择适当激励频率的结论,并提出利用相位差大小判断缺陷存在与否的方法。其次,对一套单通道低频涡流检测设备的电磁场问题进行合理的假设和定义后,建立其三维优化仿真模型,经求解分别得到有、无缺陷时试件表面涡流和感应磁场的矢量分布图,比较其感应电压曲线得出相位差;接着,分别对激励频率、信号幅度及检测线圈放置方式进行仿真计算,分析得出适合水冷壁管检测的各参数范围;并研究了不同缺陷形态下相位差的变化规律,验证了利用相位差大小判断缺陷方法的正确性。最后,通过增加检测线圈的个数增大探头扫差面积,探头在移动过程中方便的记录位置坐标和感应电压值,有效地提高了检测效率,从计算得到的相位差图形可以判断出缺陷的大致位置,并经实验验证了该方法具有一定的可行性和实用性。通过上述研究工作,为水冷壁管腐蚀多通道低频涡流检测装置提供有效的设计方案,在一定程度上提高了工作效率。更多还原

【Abstract】 The water wall tube is the main structure inside the utility boiler, so its online detection of corrosion defects has an important economic value. The low-frequency eddy current testing technology has more sensitivity on detecting the defects inside pipeline wall, so it has a very good prospect. To learn more about it how to apply the water wall effectively, the paper adopts the finite element analysis software ANSYS to carry out low-frequency eddy current testing simulation , which conclusion will provide the theoretical basis for the actual design and testing of the probe.Firstly, the article briefly introduces the principles of low-frequency eddy current testing according to the principle of electromagnetic induction, and finds out the formulas about how eddy current and electromagnetic field spread along the pipeline result from Maxwell’s equations in low-frequency eddy current testing. It reaches conclusion that detection of the inner surface defects which is obtained with different specimens needs to select the appropriate frequency, and proposes the method of according to the size of phase to judge whether defect exists or not.Secondly, it makes a reasonable assumptions and definition of issues for an one-channel device of low frequency eddy current electromagnetic field, and gets the three-dimensional simulation optimized model. After solving the model, receives the vector distribution of eddy current and magnetic field when there has or not has defect, and compares the two curves of the induced voltage. Then analyze the suit factors for water-wall tube by analyzing the frequency and signal amplitude of excitation and the pattern of detection coil place respectively,and studies the regular pattern of phase difference under different patterns of defects,which illustrates the correctness of the methods of determining whether defect exists or not based on the size of phase difference.Finally,increases the sweep area of the probe by increasing the numbers of the detection coil,records the location coordinates and the induced voltage value when it moves facilitate,the graphics of the phases can effectively determine the approximate location of defects.Through those researches, provides an effective program by designing multi-channel low-frequency eddy current testing device for the water-wall corrosion, to a certain extent, improves the work efficiency.更多还原