When employing penetrant testing, what must be ensured about the surface preparation?

In penetrant testing, ensuring that the surface is clean and dry is crucial for accurate results. This testing method relies on the ability of a penetrant to seep into surface-breaking defects. If the surface is contaminated with dirt, grease, or moisture, these substances can obstruct the penetrant's ability to enter the flaws, leading to false negative results where defects go undetected.

A clean surface allows the penetrant to interact directly with the material, while dryness ensures that there is no dilution or interference with the penetrant's performance. Maintaining a thorough cleaning process before applying the penetrant is essential to achieving reliable testing outcomes. Thus, surface preparation is fundamentally about eliminating any barriers that would prevent the penetrant from doing its job effectively.