Oil downhole metal pipe wall thickness measurement is of great importance for pipe evaluation and maintenance. Regular pipe inspection can be used to prevent pipe failure, which could otherwise lead to major failure and financial loss. In this paper, a low-frequency remote field eddy current (RFEC) based internal testing approach is presented, and the analytical solutions of the RFEC electromagnetic equation are obtained based on Dodd and Cheng’s method. Meanwhile, induced voltage under different low frequencies is analyzed, and proper frequencies are chosen for follow-up calculations. For reducing the inspection time of pipe thickness measurement, quasi-Newton’s method (QNM) is implemented based on the deduced solutions. Experimental results indicate that the RFEC and QNM based method is feasible for metal pipe thickness measurement. Pipe thickness is obtained accurately, and the lift-off effect, which has a considerable influence on eddy current testing results, is effectively overcome. The proposed method achieves pipe thickness measurement with proper accuracy and reduction in inspection time.

石油井下金属管道壁厚的测量对于管道的评估和维护非常重要。定期检查管道可用于防止管道故障，否则可能导致重大故障和财务损失。本文提出了一种基于低频远场涡流（RFEC）的内部测试方法，并基于Dodd和Cheng方法获得了RFEC电磁方程的解析解。同时，分析了不同低频下的感应电压，并选择合适的频率进行后续计算。为了减少管道厚度测量的检查时间，在推导的解决方案的基础上，采用了拟牛顿法（QNM）。实验结果表明，基于RFEC和QNM的方法对于金属管厚度测量是可行的。准确地获得了管的厚度，有效克服了对涡流测试结果有很大影响的剥离效果。所提出的方法以适当的精度实现了管道厚度的测量并减少了检查时间。