What is magnetic particle testing (MT) used for in welding inspection?

• A. Detects surface and near-surface discontinuities in ferromagnetic materials.
• B. Detects color of weld.
• C. Measures electrical resistance.
• D. Detects porosity in all metals.

Answer: (A)

Magnetic particle testing uses a magnetic field and iron particles to reveal flaws that disturb the magnetic flow in ferromagnetic materials. In welding inspection, this method is used to locate surface and near-surface discontinuities, such as cracks or seam defects, that could affect weld strength. When the part is magnetized, any flaw creates leakage fields where the magnetic flux bulges, and the iron particles cluster at those areas, making the defect visible on the surface.

This technique only works on ferromagnetic materials (like steel and certain iron alloys), so it wouldn’t be effective on non-magnetic metals. It’s specifically about finding cracks and other surface-breaking or near-surface flaws, not about assessing color, measuring electrical resistance, or detecting internal porosity in all metals—those require different nondestructive tests such as visual inspection, electrical tests, radiography, or ultrasonic testing.