Which nondestructive testing method uses a liquid penetrant to reveal surface defects?

Which nondestructive testing method uses a liquid penetrant to reveal surface defects?

• A. Magnetic particle testing
• B. Ultrasonic testing
• C. Liquid penetrant testing
• D. Radiographic testing

Answer: (C)

This method reveals surface-breaking defects by using a liquid that is drawn into tiny cracks and then made visible. The surface is cleaned and prepared, the penetrant is applied so it can seep into any openings, and after a dwell time the excess penetrant is removed. A developer is then applied, which draws the penetrant out of the flaw, creating a visible indication under suitable lighting (visible dye or fluorescent under UV). Because it relies on penetrant entering surface cracks, it’s especially good at detecting very small surface flaws, porosity on the surface, laps, and other defects that are open to the surface, and it’s relatively fast and inexpensive for many shapes and materials. However, it only shows flaws that reach the surface, so subsurface defects can be missed, and it requires clean, compatible surfaces and careful handling to avoid false indications. Other nondestructive methods work differently: magnetic particle testing uses magnetic fields to reveal surface and near-surface flaws in ferromagnetic materials; ultrasonic testing uses high-frequency sound to detect internal features; radiographic testing uses X-rays or gamma rays to image internal structures.

This method reveals surface-breaking defects by using a liquid that is drawn into tiny cracks and then made visible. The surface is cleaned and prepared, the penetrant is applied so it can seep into any openings, and after a dwell time the excess penetrant is removed. A developer is then applied, which draws the penetrant out of the flaw, creating a visible indication under suitable lighting (visible dye or fluorescent under UV). Because it relies on penetrant entering surface cracks, it’s especially good at detecting very small surface flaws, porosity on the surface, laps, and other defects that are open to the surface, and it’s relatively fast and inexpensive for many shapes and materials. However, it only shows flaws that reach the surface, so subsurface defects can be missed, and it requires clean, compatible surfaces and careful handling to avoid false indications. Other nondestructive methods work differently: magnetic particle testing uses magnetic fields to reveal surface and near-surface flaws in ferromagnetic materials; ultrasonic testing uses high-frequency sound to detect internal features; radiographic testing uses X-rays or gamma rays to image internal structures.