A penetrant inspection cannot detect which of the following?

A penetrant inspection cannot detect which of the following?

• A. An internal cavity
• B. Open to the surface discontinuities
• C. Surface cracks
• D. Through-holes open to surface

Answer: (A)

Liquid penetrant inspection works by letting penetrant enter flaws that have a path to the surface and then reveal those openings after removing excess penetrant and applying developer. Because the flaw must connect to the surface to allow entry and escape of the penetrant, a completely enclosed internal cavity with no surface opening cannot be detected—the penetrant cannot get in, nor can it be drawn out to create a surface indication. Surface cracks and discontinuities that are open to the surface provide that entry and exit path, so they produce visible or fluorescent indications after the developer step. Through-holes that are open to the surface are also detectable for the same reason—the penetrant can enter the hole and then show up on the surface as an indication.

Liquid penetrant inspection works by letting penetrant enter flaws that have a path to the surface and then reveal those openings after removing excess penetrant and applying developer. Because the flaw must connect to the surface to allow entry and escape of the penetrant, a completely enclosed internal cavity with no surface opening cannot be detected—the penetrant cannot get in, nor can it be drawn out to create a surface indication.

Surface cracks and discontinuities that are open to the surface provide that entry and exit path, so they produce visible or fluorescent indications after the developer step. Through-holes that are open to the surface are also detectable for the same reason—the penetrant can enter the hole and then show up on the surface as an indication.