Which type of crack can be detected by magnetic particle inspection using either circular or longitudinal magnetization?

• A. 45-Degree Crack
• B. Longitudinal Crack
• C. Transverse Crack
• D. Surface-Breaking Crack

Answer: (A)

Magnetic particle inspection reveals flaws by creating a magnetic field in the part and watching for flux leakage at cracks. A defect shows up where the magnetic flux is disrupted and leaks out, attracting particles to the defect location. The crack’s orientation relative to the applied field matters: if part of the crack lies across the magnetic flux, leakage occurs and the flaw is visible.

A crack oriented at about 45 degrees to the surface has a component that is perpendicular to the magnetic field whether you use circular (around the part) or longitudinal (along the length) magnetization. That means flux leakage will occur and be detectable in either magnetizing mode, making the 45-degree crack the best answer.