Influence of excitation parameters on the magnetization of MFL ILI tools for small-diameter pipelines

Magnetic flux leakage (MFL) method has been widely applied for the detection and localization of defects in pipes with nominal diameters greater than 6-inch, due to its high detection efficiency. In small-diameter pipelines, where space is constrained, achieving a high magnetic flux is vital for enhancing the sensitivity and reliability of defect detection. A well-designed excitation unit significantly improves the coupling between permanent magnets and the pipeline material, thereby maximizing the induced magnetization within the pipe wall. This aspect is particularly crucial for applications involving small-diameter pipelines ILI. The primary objective of this study is to identify the optimal dimensional parameters of the excitation unit for 4-inch MFL tools. The finite element method (FEM) was employed to analyze the evolution patterns of the magnetic field at defect sites across various operational parameters. Key factors influencing magnetization capability were examined, including magnetic core diameter, permanent magnet dimensions, lift-off height, pipe wall thickness, and operational speed. Additionally, the relationships between these influencing factors within the magnetic circuit and the induced magnetic field in the pipe wall were established. A fitting analysis of the characteristic signals was also conducted. The findings provide valuable insights into maximizing information utilization within limited space and establishing a balance between detection quality and signal precision. It is of great significance to promote the development of safety detection technology for small-diameter pipelines.