Identification and Sizing of Neighboring Pits Using Three-Axis Magnetic Flux Leakage Technique

Abstract

Abstract Neighboring corrosion pits are one of the most frequently found defects in gas pipelines. Because of the interaction with each other, these defects accelerate the corrosion growth rates in the wall of the pipelines. Hence, it is meaningful to discriminate multiple neighboring pits from single isolated pits by analyzing their characteristics. This article presents the results of a study on the use of a three-axis magnetic flux leakage (MFL) technique for the identification and sizing of neighboring corrosion pits. Various patterns of two neighboring pits are considered by modifying the separation distances between them. Finite element modeling as well as experimental measurements is used to investigate the spatial distributions of the three MFL components (axial, radial, and circumferential) generated by the neighboring pits. The results indicate that the axial as well as the radial MFL components of the neighboring pits merge to one signature the closer the two defects are, and thus, no width sizing of the individual pits is possible anymore. In contrast, both pits are still discernible in the circumferential MFL signatures. The described method can help to identify neighboring corrosion pits and thus improve the sizing accuracy of MFL measurements.