Magnetic Anomaly Detection of Defects in Underground Ferromagnetic Pipeline Using Variational Mode Decomposition and Scale-space Segmentation

The study aimed to investigate the use of Magnetic Anomaly Detection (MAD) to locate defects in underground ferromagnetic pipelines without exposing them, which presented a large advantage over current methods. MAD has received much attention in recent years because it has many possible applications in detecting and locating ferromagnetic targets, especially for ferromagnetic pipelines. However, the accuracy of MAD is limited due to disturbs from the geomagnetic field and other sources around. The current investigation involved Variational Mode Decomposition and Scale-Space Segmentation (VMD-SSS) to improve the performance of MAD for pipeline defects. Variational Mode Decomposition (VMD) is the algorithm decomposes signals into different modes, which is a revised version of the Empirical Mode Decomposition (EMD) for analyzing non-linear and non-stationary signals. Since the geomagnetic signal is also a non-linear and non-stationary signal, and pipeline defects will affect the geomagnetic signal, it is crucial to study the bandwidth estimation of instantaneous frequency (IF) and instantaneous amplitude (IA) spectrum based on the mode. In the present work, VMD was employed to reconstruct the magnetic anomaly signals to create an effective detector, which can be used to decompose the magnetic anomaly signal into different modes accurately. The input parameters of VMD were optimized using Scale Space Segmentation (SSS), and the anti-noise performance was compared. It was noticed that VMD-SSS served as an effective tool in both extracting the time-frequency characteristics of magnetic anomaly signals and the coupling analysis of magnetic field signals between different frequency bands. The results of applying VMD-SSS in experiments showed that the peak of the coupling strength appeared when the frequency band was less than 1 Hz, and pipeline defects could be located by using the specified frequency band signal with an error of no more than 5%. The VMD-SSS method presented in the paper can be used to describe the energy coupling characteristics of the magnetic anomaly signals at different time-frequency scales and provides support for studying the mechanism and characteristics of MAD in ferromagnetic pipeline defect.