Design and Manufacturing of the Magnetic Flux Leakage Inspection System for Detection of Pitting Corrosion in Gas Pipelines

The magnetic flux leakage technique (MFL) is a widely used method for corrosion detection in the gas pipelines. The inspection of pipelines is typically performed using intelligent PIGs. The MFL intelligent PIG is equipped with an array of magnetizers responsible for inducing a magnetic field in the pipeline wall. The magnetic field leaks out of the pipeline wall at the locations where defects are present. The magnitude of the leakage magnetic field is measured by Hall-effect sensors and used for analysis of defects. In recent studies, the design of the appropriate magnetizer, as a technique to improve the probability of detection of the MFL, has been of great interest to the researchers. In this study, the simulation of the MFL technique was carried out based on Maxwell equations and in 3D using COMSOL software. The specimen under test was a carbon steel plate with a thickness of 10mm, which contained two pitting defects with various depths of 4mm and 6mm. Then, the MFL signals obtained from the defects were analyzed. Following the finite element modeling and obtaining the magnetizer dimensions, MFL system was designed and manufactured. First, the FEM results were experimentally validated. The results of the comparison indicated that there was a good agreement between experiments and FEM. The mean error was below 9%. Finally, MFL experiments were carried out and C-scans from the defects of different depths were obtained. The C-scans can be used for characterization of the defects.