The simulation and experimental analysis of the MFL for cracks inspection in pipelines under mechanics-magnetic coupling

摘要

Since the magnetic flux leakage (MFL) for cracks inspection in pipelines can be influenced by stress concentration, it is very difficult to characterize and size the crack or crack-like defects. Thus, the theory model of magnetization and permeability under mechanics-magnetic coupling was derived by thermodynamic equation firstly, and the effects of the applied stress on magnetization and permeability were analyzed theoretically. The finite element method (FEM) under mechanics-magnetic coupling was studied, and the relationship of the crack's MFL and loaded stresses were simulated and studied using the 3D FEM. And the simulation results were verified by experiments with the help of material testing system (MTS). The simulation and experimental results demonstrate that the experimental results are basically consistent with simulation results, and the MFL density caused by cracks decreases with the applied stress increasing gradually. Therefore, the higher sensitivity sensors should be employed in the MFL measurement for pipeline cracks and the testing data should be compensated while quantitative interpretation.