Research on the magnetic flux leakage field distribution characteristics of defect in low-frequency electromagnetic detection technique

Abstract

This work aimed to investigate the distribution characteristics of the low-frequency magnetic flux leakage (LF-MFL) field of defect on oil and gas pipelines in low-frequency electromagnetic detection technique (LFET). Taking four types of crack defects (rectangular, semicircular, trapezoidal, and V-shaped grooves) with equal lengths, widths and different bottom shapes into consideration, the specific mathematical model of the LF-MFL field was inferred and established on the basis of magnetic dipole theory. Experimental results demonstrated that the variation values of the tangential and normal component upper-lower envelope difference curves were linearly positively correlated with the defect cross-sectional area along the detection direction, which was strictly independent of bottom shape and excitation conditions (amplitude, frequency and lift-off).