In magnetic particle inspection, a flaw that is perpendicular to the magnetic field flux lines generally causes

• A. No effect
• B. A bright visualization
• C. A small color change on the surface
• D. A large disruption in the magnetic field

Answer: (D)

Magnetic particle inspection relies on how magnetic flux travels through a material and how surface particles reveal changes when flux leaks out near flaws. When a flaw sits across the direction of the magnetic field, it presents a high-reluctance path and interrupts the smooth flow of flux. The field lines must bend and concentrate around the flaw, creating a leakage field at the surface. This leakage attracts magnetic particles and produces a strong, visible indication. So, the perpendicular orientation causes the most disruption to the magnetic field, making the defect easy to detect with a bright, clear indication.