The term used to define the tendency of certain liquids to penetrate into small openings such as cracks or fissures is

The term used to define the tendency of certain liquids to penetrate into small openings such as cracks or fissures is

• A. Viscosity
• B. Capillary action
• C. Surface tension
• D. Diffusion

Answer: (B)

Capillary action describes how liquids are drawn into small spaces because the liquid clings to the walls (adhesion) and the molecules hold together (cohesion). In liquid penetrant testing, the penetrant must wet the crack walls, so adhesion between the penetrant and the material pulls the liquid into narrow cracks, often against gravity. The smaller the opening, the stronger the capillary rise, which helps the penetrant fill flaws that are difficult to see. Viscosity is about how easily a liquid flows, but it doesn’t define the tendency to enter tiny openings. Surface tension affects wetting at the surface, and diffusion is about how substances spread, but neither describes the mechanism that causes penetration into narrow cracks as capillary action does.

Capillary action describes how liquids are drawn into small spaces because the liquid clings to the walls (adhesion) and the molecules hold together (cohesion). In liquid penetrant testing, the penetrant must wet the crack walls, so adhesion between the penetrant and the material pulls the liquid into narrow cracks, often against gravity. The smaller the opening, the stronger the capillary rise, which helps the penetrant fill flaws that are difficult to see. Viscosity is about how easily a liquid flows, but it doesn’t define the tendency to enter tiny openings. Surface tension affects wetting at the surface, and diffusion is about how substances spread, but neither describes the mechanism that causes penetration into narrow cracks as capillary action does.