Numerical Modeling and Experimental Study of MFL Technique for Detection of Sub-surface Pittings in Pipelines

Numerical Modeling and Experimental Study of MFL Technique for Detection of Sub-surface Pittings in Pipelines

Magnetic flux leakage (MFL) technique is currently the most commonly used method for corrosion monitoring in oil and gas pipelines. The present work employs 3D finite element modeling (FEM) to investigate the performance of MFL technique in detecting sub-surface pittings in pipelines. In order to simulate sub-surface pitting corrosion of oil and gas pipelines, rectangular pittings with different depths are modeled on a 10mm-thick steel plate. Then, the axial and radial components of MFL signals are obtained to investigate the influence of defect depth on detectability of sub-surface pittings by the MFL technique. Also, the influence of lift-off distance on MFL signals has been analyzed for enhancing the reliability of detection of defects. The results indicate that the designed magnetizer assembly renders detectability of pittings located at 9mm below surface in a 10mm-thick steel plate, which can meet the industry demand for in-service inspection. The MFL signals have also been obtained experimentally using an experimental set-up at the laboratory facilities on a steel plate containing sub-surface pittings. A good agreement between FEM and experimental results confirms that 3D FEM is an effective analysis method for MFL technique in the pipeline inspection.

Magnetic flux leakage (MFL) technique is currently the most commonly used method for corrosion monitoring in oil and gas pipelines. The present work employs 3D finite element modeling (FEM) to investigate the performance of MFL technique in detecting sub-surface pittings in pipelines. In order to simulate sub-surface pitting corrosion of oil and gas pipelines, rectangular pittings with different depths are modeled on a 10mm-thick steel plate. Then, the axial and radial components of MFL signals are obtained to investigate the influence of defect depth on detectability of sub-surface pittings by the MFL technique. Also, the influence of lift-off distance on MFL signals has been analyzed for enhancing the reliability of detection of defects. The results indicate that the designed magnetizer assembly renders detectability of pittings located at 9mm below surface in a 10mm-thick steel plate, which can meet the industry demand for in-service inspection. The MFL signals have also been obtained experimentally using an experimental set-up at the laboratory facilities on a steel plate containing sub-surface pittings. A good agreement between FEM and experimental results confirms that 3D FEM is an effective analysis method for MFL technique in the pipeline inspection.