Which nondestructive testing method uses magnetic fields to detect surface or near-surface flaws?

Which nondestructive testing method uses magnetic fields to detect surface or near-surface flaws?

• A. Magnetic particle testing
• B. Ultrasonic testing
• C. Radiography
• D. Dye penetrant testing

Answer: (A)

Magnetic particle testing relies on magnetic fields to reveal flaws that interrupt the metal’s normal magnetic flux. When a ferromagnetic part is magnetized, any crack or near-surface discontinuity distorts the magnetic field and creates leakage flux at the defect. Applying iron particles (dry or in liquid) makes this leakage visible: the particles are drawn to the leakage area and form a visible indication that outlines the flaw’s location and orientation. This method is especially effective for surface-breaking and near-surface defects in ferromagnetic materials like steel and cast iron. It does require proper surface cleaning and is limited to magnetic materials. Other listed methods use different principles—ultrasonic testing uses sound waves, radiography uses penetrating radiation, and dye penetrant relies on surface wetting to reveal flaws—so they don’t rely on magnetic fields to detect flaws.

Magnetic particle testing relies on magnetic fields to reveal flaws that interrupt the metal’s normal magnetic flux. When a ferromagnetic part is magnetized, any crack or near-surface discontinuity distorts the magnetic field and creates leakage flux at the defect. Applying iron particles (dry or in liquid) makes this leakage visible: the particles are drawn to the leakage area and form a visible indication that outlines the flaw’s location and orientation. This method is especially effective for surface-breaking and near-surface defects in ferromagnetic materials like steel and cast iron. It does require proper surface cleaning and is limited to magnetic materials. Other listed methods use different principles—ultrasonic testing uses sound waves, radiography uses penetrating radiation, and dye penetrant relies on surface wetting to reveal flaws—so they don’t rely on magnetic fields to detect flaws.