Study on the Influence of Spacing of the Nearby Corrosion Defects on MFL Signals

Magnetic flux leakage (MFL) technique is a widely used and effective approach for detecting and sizing of the corrosion defects in ferromagnetic pipelines. In general, corrosion defects occur in dense clusters and affect each other. However due to the interaction between the MFL signals, these defects can-not be accurately characterized using the traditional MFL method. In order to discriminate the individual defects and improve sizing performance, tri-axial MFL technique is used. The study is performed using the extensive finite element modeling (FEM) focusing on the spatial distribution of tri-axial MFL components produced by the nearby corrosion defects. This type of defect geometry comprises two pits that are sufficiently close to influence flux distributions in the area between them. Various degrees of closeness are considered by varying the spacing of the two pits. Following the simulations, experimental MFL tests are performed on the steel plates containing nearby pits. The experimental and FEM results indicate that combining the axial, radial and circumferential MFL data can discriminate and characterize the nearby pits. Finally, the experimental and FEM results are compared.