铁磁性套管脉冲涡流检测的时域解析解

Time-domain analytical solutions of pulsed eddy current testing on ferromagnetic casing

脉冲涡流检测因具有低功耗、响应频谱宽、对不同深度缺陷具有较高灵敏度等特点而愈发受到重视。然而当前多数套管检测研究均使用电流源作为激励,由于激发线圈存在自感,其在电流脉冲激励信号的上升和下降沿将产生一个极大的反向瞬时感应电压。因此在这类研究中,对电流源激励的功率和稳定性提出了极高的要求。为解决电流型脉冲激励的上述问题,给出一种电压型脉冲激励套管涡流检测方法并推导了其时域解析解。首先,分析了激发线圈自感及套管涡流对激励电流的影响。然后,使用了更为准确的脉冲激励函数进行解析计算,并通过磁场叠加推导了激励、涡流磁场在接收线圈中的时域感应电压解析解。实验表明,得出的解析计算结果与实验电流、感应电压的相对误差分别为2.9%和9.6%,提升了理论数据的准确性。

The pulsed eddy current testing(PECT) attracts increasing attention because it is sensitive to different depth defects and has advantages of low power dissipation and abundant frequency spectrum. Recent studies apply current excitation based pulsed eddy current for metal material testing. Due to the inductance to the coil, it leads to a large reverse induced electromotive force in a driver coil at the rising and falling edges of pulse excitation. The phenomenon means that high performance of power and stability should be utilized for testing. To solve the aforementioned problems of the excitation circuit, a voltage excitation based ferromagnetic casing PECT method is proposed. The time-domain analytical solution of the testing is formulated. The influences of the self-inductance of the driver coil and the casing eddy current on the excitation current have been analyzed. Then, a more precise pulse excitation function is used for the calculation of the analytical solution. And the analytical solutions of the induced electromotive force to pick-up coils are formulated based on the superposition of the excited and induced magnetic field. Finally, experimental results indicate that better accuracy is achieved based on the proposed analytical solutions. The relative errors of excitation current and induced electromotive force between the theoretical and experimental results are 2.9% and 9.6%, respectively.