A study on the measurement of axial cracks in the Magnetic Flux Leakage NDT system

Among the nondestructive testing methods, the MFL(Magnetic Flux Leakage) PIG(Pipelines Inspection Gauge) is especially suitable for testing pipelines because the pipeline has high magnetic permeability. MFL PIG showed high performance in detecting the metal loss and corrosions. However, MFL PIG is difficult to detect the crack which occurred by exterior-interior pressure difference in pipelines and the shape of crack is very long and narrow. Therefore, the new PIG is needed to be researched and developed for detecting the cracks. The CMFL(Circumferential MFL) PIG performs magnetic fields circumferentially and can maximize the magnetic flux leakage at the cracks. In this paper, CMFL PIG is designed and the distribution of the magnetic field is analyzed by using finite element method. Also, by simulating and measuring the magnetic leakage field, it is possible to detect of axial cracks in the pipeline.