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

In penetrant testing, ensuring that the surface is clean and dry is critical for the success of the process. This method involves applying a liquid penetrant to the surface of a material to find defects such as cracks, porosity, or other discontinuities. For the penetrant to effectively fill any surface voids and adhere appropriately, contaminants such as oil, dirt, rust, or moisture must be removed from the surface. If the surface is not clean and dry, it can lead to false readings or missed defects, as the penetrant may not be able to infiltrate the flaws properly. Therefore, the emphasis on cleanliness and dryness is essential for accurate inspection results.