Finite Element Modeling of Magnetic Flux Leakage from Metal Loss Defects in Steel Pipeline

Abstract

Magnetic flux leakage is a nondestructive method for inspection of steel pipelines carrying petroleum products, and is most widely used technique. The inspection tool used for this purpose is called instrumented pipeline inspection gauge (IPIG) which moves with the pressure of fluid inside the pipeline. In this paper, a three-dimensional finite element modeling and static simulation of the magnetic circuit of a magnetic flux leakage-based IPIG has been carried out. A FEM-based MagNet software has been used. Rectangular defects of different dimensions on a plate have been modeled, and the magnetic flux leakage response from each of these defects has been studied. Appropriate properties and boundary conditions have been imposed in the simulation. The dependency of some of the characteristic defect dimensions and the leakage flux signal has been studied. In addition, the effect of sensor liftoff on the leakage flux values for specific defect geometry has been studied and understood. Furthermore, the effect of defect orientation on the internal or external surface as against the sensor positioning has also been studied. A comparison of the FEM-simulated flux values with that of experimental leakage flux values has been made.