Influences of Magnetization Direction on the Flux Leakage Field of Weld Defects

Abstract

The magnetic flux leakage (MFL) detection technique is applied to the detection of weld defects, such as cracks and pores. As the weld has a distinct structure, there are differences in the magnetization path and leakage field intensity under different magnetization directions. According to surveys, a suitable magnetization direction can significantly enhance detection rates of small-sized defects by stimulating a stronger field signal of the defect leakage. In this study, ANSYS finite element simulation software is used to calculate the weld defect leakage field based on the quantitative analysis. Specifically, the leakage field component strengths of circular hole defects and longitudinal rectangular groove defects are compared when the magnetization direction is perpendicular or parallel to the weld. Furthermore, the characteristic rules of the defect leakage field and its components under any magnetization direction are discussed, and a weld MFL detection platform is set up for validation. According to the experimental results, the amplitude of the magnetic leakage signal during vertical magnetization of circular hole defects is only 18.6% of that during parallel magnetization. Similarly, the amplitude of the magnetic leakage signal during parallel magnetization of longitudinal crack-type defects is only 9.2%~29.3% of that during vertical magnetization.