The penetrant applied to the surface of a test specimen is drawn into discontinuities by:

The penetrant applied to the surface of a test specimen is drawn into discontinuities by:

• A. Gravity
• B. Electrical attraction
• C. Capillary action
• D. Chemical reaction

Answer: (C)

Capillary action is the movement of a liquid into narrow spaces because of adhesive forces between the liquid and the material and cohesive forces within the liquid. In liquid penetrant inspection, the penetrant wets the surface and is drawn into tiny cracks, voids, and other discontinuities by these capillary forces. The small openings act like capillary channels, so the liquid rises and flows into the defects, even when gravity isn’t the primary driver. Gravity, electrical attraction, and chemical reactions don’t cause the penetrant to enter discontinuities—the capillary action does.

Capillary action is the movement of a liquid into narrow spaces because of adhesive forces between the liquid and the material and cohesive forces within the liquid. In liquid penetrant inspection, the penetrant wets the surface and is drawn into tiny cracks, voids, and other discontinuities by these capillary forces. The small openings act like capillary channels, so the liquid rises and flows into the defects, even when gravity isn’t the primary driver. Gravity, electrical attraction, and chemical reactions don’t cause the penetrant to enter discontinuities—the capillary action does.