Classifying internal and external wall defects in ferromagnetic pipelines utilizing an asymmetric "M-shaped" magnetizer

Abstract

Accurate classification of internal and external defects in pipelines is crucial, as defects of the same size can have different impacts based on their location. This study introduces a method for distinguishing between internal and external defects using magnetic permeability perturbation testing (MPPT), which is known for its high sensitivity to micro defects of ferromagnetic components. This method employs an asymmetrical "M-shaped" magnetizer, using pole shoes of different thicknesses to achieve layered magnetization. By analyzing the differences in MPPT signals to classify defects effectively. A magnetic circuit model and a finite element simulation model with varying pole-shoe thicknesses were established, revealing that varying the pole-shoe thickness can change the magnetization level. An experimental platform was constructed to validate the simulation results. Theoretical and experimental analyses demonstrate that the method is user-friendly, highly efficient in detection, and capable of classifying internal and external defects of various sizes on ferromagnetic components with a thickness of 20 mm. Notably, the method shows resilience against variations in defect size and component thickness. Selecting the optimal combination of pole shoe thicknesses can help improve classification accuracy. This straightforward and practical method holds significant potential for the classification of internal and external defects, providing substantial value in non-destructive testing applications.