Factors affecting magnetic flux leakage inspection of drill pipes

Abstract

Abstract The magnetic flux leakage (MFL) method is a highly effective non-destructive testing technique, widely used for inspecting drill pipes in oil and gas fields. This paper demonstrates, through numerical simulations, the influence of essential parameters such as the magnetization system, defect size and orientation, lift-off distance, pipe wall thickness and scanning speed on the inspection sensitivity. The analysis of the magnetization system confirms the ability of Helmholtz coils to create a strong and uniform magnetic field following the scanning direction; making this method more suitable for detecting transverse defects. To improve inspection sensitivity, the study highlights the necessity of adding a ferrite core to provide a Lift-Off-Tolerant magnetic flux inspection. Additionally, the optimal scanning speed depends on pipe wall thickness, its magnetic saturation and whether the inspection concerns the top or bottom surface.