Magnetic Hysteresis Analysis of a Pipeline Re-Inspection by Using Preisach Model

The magnetic-flux leakage (MFL)-type pipeline inspection is a method of inspecting the pipe by detecting the leaked magnetic flux due to defects after applying a large magnetic field, and there is an advantage that even a small defect can be found regardless of the inner and outer walls of the pipe. In addition, since the MFL pipeline inspection gauge, called MFL pipeline inspection gauge (PIG), can be moved by the gas pressure in pipes, it is widely used for pipeline inspection including buried pipelines. However, after performing the MFL-type pipeline inspection, the remanent magnetization remains on the pipes due to the large applied magnetic field and magnetic hysteresis of pipe, which affects the subsequent inspection signal. However, since the direction of the MFL-type pipeline inspection depends on the direction in which the gas flows, it cannot always be inspected in the same direction. Moreover, since the remanent magnetization has different effects on the inspection signal depending on the subsequent inspection direction, it is necessary to analyze the effects of the remanent magnetization on the inspection signal considering the inspection direction. In this article, the remanent magnetization due to MFL PIG is analyzed using the Preisach model, and the effect of the remanent magnetization on the subsequent inspection considering the inspection directions is analyzed using the finite-element analysis. The results of the analysis are verified through experiments.