Investigation of the Lift-off Effect on the Corrosion Detection Sensitivity of Three-axis MFL Technique

Lift-off is considered as one of the most critical parameters that poses a major challenge in the appropriate application of magnetic flux leakage inspection technique. Sediments and welds are presented in the internal of all pipelines and cause lift-off. This paper investigates the influence of lift-off distances on the components of the three-axis MFL technique and, therefore, the lift-off effect on the corrosion detection sensitivity. COMSOL software is used to set up the 3D FEM modeling of three-axis MFL technique. In order to simulate internal pitting corrosion of oil and gas pipelines, two adjacent pits of different depths are modeled on the surface of a carbon steel plate. At a range of lift-off values, MFL responses from this defect geometry are computed and the relationships between the lift-off distances and obtained MFL signals are analyzed in detail. Finally, the validity of the simulation results is verified by experimental tests.