Magnetic Barkhausen Noise Testing for Subsurface Discontinuities under DC Magnetization

Subsurface discontinuities are inevitably formed during the long-term operations of pipelines, oil tanks, ship hulls, and the like. However, it is still a big challenge to detect deeply buried subsurface discontinuities using existing nondestructive testing methods. In this paper, based on the high sensitivity of magnetic Barkhausen noise (MBN) to the movement of the domain walls, an MBN test under direct current (DC) magnetization is proposed for subsurface discontinuity detection. Under DC magnetization, subsurface discontinuities will distort the magnetic field distribution in the near-surface layer of the specimen and then affect the movement of the domain walls in this region. Meanwhile, through alternating current (AC) excitation, MBN testing is conducted to detect the movement of the domain walls to evaluate subsurface discontinuities. To validate the proposed technique, MBN experiments under DC magnetization are conducted to quantify subsurface discontinuities with different buried depths. Experimental results indicate that the proposed technique can detect subsurface discontinuities with buried depths of up to 5 mm, and the extracted MBN energy feature has an approximately linear relationship with the buried depth.