基于多频交流场指纹法的金属管道腐蚀监测研究

中文摘要: 在油气管道腐蚀检测领域，场指纹法（field signature method，FSM）管道腐蚀在线监测技术是一种运用较为普遍的技术。然而传统的场指纹技术还存在诸多不足，例如极易受到系统漂移的干扰而导致监测结果出现较大偏差；需要数十安培的激励电流，电源模块易损坏，只能测量相对壁厚减薄，参考板与被测管道之间的温度差会引入很大的测量误差等。作者在有限元仿真的基础上，提出了一种多频交流场指纹技术（multi-frequency alternative current field signature method，MACFSM）。在仿真计算中，依次向被测金属管道注入频率从高到低的交流激励电流，根据趋肤效应，趋肤深度随着频率的降低而增大，使得测量电极间的电压逐渐减小，当趋肤深度增大到管壁壁厚之后，随着频率的进一步降低，测量电极间的电压将保持稳定。将测量得到的电压序列进行求导，得到了导数极值，利用导数极值即可求解出缺陷的深度。最后利用实验对仿真进行了验证，向缺陷深度为3.5 mm的被测金属管道注入了0.1 A的多频激励电流，准确地利用导数极值求解出了缺陷深度。仿真和实验表明，MACFSM将不再需要参考电压，也不需要原始电压，更不需要对原始壁厚进行精确测量，而且可以有效克服系统漂移的影响，降低激励电流幅值，提高了作为长期在线监测技术的可靠性。
Abstract:Field signature method (FSM) is a common monitoring technology for metal pipeline corrosion. However, there are a lot of shortcomings in FSM Technology such as the measurement results are easily disturbed by the drift and the temperature difference between the reference plate and the measured pipe will lead to a large measurement errors. Multi-frequency alternative current field signature method (MACFSM) is introduced to assess the wall thickness of metal pipeline based on finite element simulation. Multi-excitation current with a series of frequency from high to low is injected into the measured metal pipe, and penetration depth will increase with decreasing frequency while voltage between electrodes will decrease. When penetration depth reach to the inner wall of measured pipe, voltage between electrodes will remain the same. Therefore, all of the recorded voltages can be fitted into a function, then take the derivative of this function, while the penetration depth of the first zero of derivative is equal to the wall thickness of the measured pipe. Then, the experiment was applied to verify the simulation. 0.1 A multi frequency exciting current was injected into the metal pipeline with a defect depth of 3.5 mm, and the defect depth was solved accurately by the derivative extreme value. The simulation and experiment showed that multi-frequency alternative current Field signature method (MACFSM) does not need reference voltage, and the measured voltage also does not need to be compared with original voltage; especially this method can overcome the adverse effect caused by baseline drift of electric circuit system and change in temperature, therefore the reliability of long term on-line monitoring technology can be greatly improved.