A Quantitative Detection Approach for Microcrack in High Steel Pipeline By Motion Induced Eddy Current Technique

Oil and gas pipelines were widely applied in petrochemical, construction, metallurgy and other fields. The microcracks are appeared on the pipeline wall due to the harsh working conditions, which can trigger the oil or gas leakage incidents. However, the geometric parameters of the microcarcks are tiny and the signals are weak. It is a challenge for the existing nondestructive testing techniques. To quantitatively detect the microcracks in the internal surface of the pipeline online, a motion induced eddy current (MIEC) technique based on permanent magnet is proposed in this paper. Firstly, the mechanism of MIEC technique based on permanent magnet is analyzed; Then, the finite element model of MIEC technique for pipeline detection is established; Followed that the relationship between the characteristic signal and microcrack depth/width are investigated and the probe parameters of the MIEC technique based on permanent magnet are optimized; Then, a quantitative and online detection approach for the microcracks in the internal surface of the pipeline is proposed, which is based on MIEC The investigation indicated that the width of the crack is dependent of the peak value arrival time of $\Delta B_{\mathrm{x}}$ or $\Delta B_{\mathrm{z}}$, and the depth of the crack is monotonic changing with the $\Delta B_{\mathrm{x}}$ and $\Delta B_{\mathrm{z}}$. The case study indicated that the characterization error is less than 10% when the crack width is larger than 0.1mm when the detection speed is 5m/s. This approach not only can be applied for the microcracks detection for the pipeline but also can be applied in the microcracks in the running component, such as the microcracks in the rail track and running axle.