Which statement about viscosity and penetrant performance is true?

• A. Affects the speed of penetration but not the penetration ability
• B. Viscosity changes the color of the penetrant
• C. Viscosity has no effect on penetration speed
• D. Viscosity makes penetrant magnetic

Answer: (A)

Viscosity primarily governs how quickly penetrant can flow into flaws, not whether it can enter them at all. In liquid penetrant inspection, capillary action and surface wetting drive penetration. A lower-viscosity penetrant flows into narrow, deep defects faster, increasing the speed of penetration. But given proper surface preparation, compatible chemistry, and adequate contact time, the penetrant can enter flaws even if its viscosity is higher—the key difference is how fast it happens, not whether it happens. The other statements misstate viscosity’s role: viscosity doesn’t change the color of the penetrant (that’s the dye/developer), it does affect penetration speed, and it has nothing to do with magnetism.