Which non-destructive examination method uses magnetic fields to detect defects?

• A. Magnetic Particle (MT)
• B. Radiographic (RT)
• C. Ultrasonic (UT)
• D. Visual inspection (VT)

Answer: (A)

Magnetic fields are used to reveal flaws in ferromagnetic materials by making defects stand out where the magnetic flux leaks. When a magnetized part contains a discontinuity that reaches or nears the surface, the magnetic field is distorted at that flaw. If magnetic particles are applied—either as dry iron filings or in a fluorescent suspension under proper lighting—these particles accumulate at the leakage region and form a visible indication that marks the location of the defect. This makes it a quick, portable, and effective way to detect surface-breaking and near-surface flaws, especially in welds and steel components.

Keep in mind this method works best on magnetic materials like steel and iron. It won’t reliably detect deep interior flaws in non-magnetic materials, and proper surface preparation and magnetization in the correct orientation are important to reveal defects that may be oriented in different directions.