What does 'permeability' refer to in relation to penetrants?

Permeability in relation to penetrants refers to the ability of the penetrant to pass through the surface of a material, which is essential for detecting surface-breaking defects. High permeability allows the penetrant to effectively seep into cracks or other discontinuities, which is crucial for ensuring accurate and reliable inspection results. This characteristic is vital for the efficacy of liquid penetrant testing, as it directly influences how well the penetrant can highlight defects that might compromise the integrity of the material being inspected. By allowing the penetrant to enter these flaws, inspectors can effectively determine the presence of defects by later applying a developer, which draws the penetrant out and creates a visible indication of any flaws present.