油气长输管道裂纹漏磁检测的瞬态仿真分析

为了提高油气管道漏磁检测的准确度,应充分考虑检测器行进速度对漏磁信号的影响。根据三维有限元分析原理,建立了漏磁检测系统的瞬态数学模型,并对油气长输管道裂纹检测过程进行了仿真研究。由麦克斯韦方程组推导出管道裂纹静态漏磁场的分布模型,对由漏磁检测器运动产生感应的管壁环向涡流进行了定量分析,计算其形成的"逆磁场"及其对外加磁场的影响,推导出动态磁化条件下的裂纹漏磁场有限元仿真模型。由实际物理实验得到与仿真分析相一致的漏磁信号,这表明所建瞬态仿真模型的有效性。利用该模型,获得了不同裂纹所产生的漏磁信号检测结果。根据检测结果,分析了裂纹几何特征,如深度、宽度等与漏磁信号峰谷值之间的对应关系,并给出了关系曲面图。为实际利用漏磁信号检测油气长输管道裂纹提供了重要的依据。

Transient simulation analysis on magnetic flux leakage detection of cracks in long-distance oil and gas pipeline

In order to improve the accuracy of magnetic flux leakage (MFL) detection for the long-distance oil and gas pipeline, the impact of the moving velocity of detector on MFL signals should be carefully considered. According to the principle of 3D finite element analysis, a transient mathematic model for the MFL testing system was established and used to stimulate and analyze the crack detection process of oil and gas pipeline. A model for the static MFL distribution of pipeline crack was derived from the Maxwell’s equations.Based on the model, the circumferential eddy current of pipeline generated from the movement of the detector was quantitatively analyzed, furthermore, the characteristics of inverse magnetic field formed by the eddy current and its effect on the external magnetic field were evaluated. Finally, a finite element simulation model for the magnetic flux leakage of crack was derived under the condition of dynamic magnetization. The model can acquire the tested results of MFL signals corresponding to different cracks. The consistency between the actual physical experiments and simulation analysis of the MFL signals proved the effectiveness and correctness of the transient simulation model. The relations of the crack geometric parameters, such as depth, width and the peak-valley value of MFL signals were discussed, and their relative curved surface plots were also drawn. The results of simulation analysis may be as a reference for practical MFL detection of cracks in long-distance oil and gas pipelines.