Feature Enhancement Method for Magnetic Particle Testing Based on Isolation Strip

Magnetic particle testing (MT) has the advantages of high sensitivity and adaptability. However, during the formation of magnetic particle indication (MPI) corresponding to surface opening defects, the defects are filled with magnetic particles, resulting in the weakening of the leakage magnetic field (LMF), a phenomenon that has been ignored in existing studies. In order to enhance the visual feature of MPI, this article proposes an isolation strip-based MT method (ISMT), which can avoid the attenuation of LMF. Meanwhile, ISMT can isolate the surface conditions of the specimen to avoid the formation of pseudo-MPI (PMPI). The enhancement principle of ISMT is analyzed by simulation. Comparative experiments between ISMT and traditional MT were conducted to verify the visual enhancement effect of ISMT on defects of multiple depths. The results show that the enhancement effect of ISMT is 1.51 times, 1.36 times, and 1.08 times for the standard test shims of 60/100, 30/100, and 15/100, respectively. In addition, the advantage of ISMT in detecting larger defects is verified by experiments on hole defects of different sizes, and the isolation effect against surface oil stains is discussed.