Liquid Penetrant Testing Level 1 (PT-1) Practice Exam

Which of the following characteristics is NOT required of a good penetrant?

1. Having high viscosity

2. Evaporating very rapidly

3. Providing good contrast

4. Permanently penetrating into defects

The correct answer is: Evaporating very rapidly

A good penetrant should ideally have characteristics that enhance its ability to detect surface-breaking flaws in materials. Rapid evaporation is not desirable because the penetrant needs adequate time to flow into any defects before the excess is removed. If a penetrant evaporates too quickly, it may not fully penetrate into the flaws, leading to false negatives in the inspection process. On the other hand, high viscosity is beneficial as it allows the penetrant to remain on the surface longer, minimizing the likelihood of running off and ensuring maximum penetration into any defects. Providing good contrast is essential for visibility; a penetrant that contrasts well against the substrate makes it easier to identify indications. Lastly, the penetrant needs to permanently fill defects to ensure that any flaws can be accurately detected and diagnosed during the inspection process. Therefore, while effective penetrants should exhibit low viscosity for better flow characteristics and provide the necessary properties for quality inspections, rapid evaporation is not a requirement for a good penetrant.