A Method Using Magnetic Eddy Current Testing for Distinguishing ID and OD Defects of Pipelines under Saturation Magnetization

Abstract

Distinguishing the inside (ID) and outside (OD) defect is an essential problem for the oil and gas pipeline nondestructive testing in engineering. The most widely used solution is to combine a magnetic flux leakage (MFL) section and a second section. For the strong magnetic field environment of the MFL, the second section and the MFL section are usually located at different mechanical positions, which leads to an increase in the length of the pipeline inspection gauge (PIG) and a decrease in the reliability. In this paper, a new impedance measurement method and the concept of the defect impedance angle are proposed to distinguish the ID and OD defects of pipelines under saturation magnetization, which based on the magnetic eddy current testing (MECT). The proposed ID & OD detection method can work with the MFL in the same mechanical position. Meanwhile, the proposed method also has the advantage that the discrimination criteria of the ID and OD defect keeps consistent with the classic eddy current testing (ECT). Furthermore, the robustness and sensitivity of the proposed method are discussed and verified by physical experiments.