NDT - Non-Destructive Testing Liquid Penetrant Testing Process Questions and Answers — Questions and Answers
Question 1: An NDT technician applies a visible dye penetrant to a non-porous component. After the appropriate dwell time, the excess penetrant is removed, and a non-aqueous wet developer is applied. Which of the following is the PRIMARY function of the developer in this process?
- To chemically react with the penetrant and change its color for better visibility.
- To provide a protective coating over the test surface to prevent contamination.
- To act as a solvent that dissolves the penetrant trapped in discontinuities.
- To act as a blotter, drawing the penetrant out of discontinuities to form a visible indication. (Correct answer)
Correct answer: To act as a blotter, drawing the penetrant out of discontinuities to form a visible indication.
The primary function of the developer is to act like a blotter. It has a high absorbency that draws the penetrant trapped within surface-breaking discontinuities back to the surface through capillary action. This allows the small amount of trapped penetrant to spread out, creating a visible indication that is much larger and easier to see than the actual discontinuity.
Question 2: A liquid penetrant inspection is being performed on an aluminum casting. Which of the following pre-cleaning methods would be considered detrimental to the inspection's sensitivity because it might close or smear over the very discontinuities the test is designed to find?
- Vapor degreasing
- Wiping with a solvent-moistened lint-free cloth
- Grit blasting (Correct answer)
- Alkaline cleaning
Correct answer: Grit blasting
Aggressive mechanical methods like grit blasting, shot peening, or power wire brushing can smear the metal surface, closing the openings of small discontinuities. This prevents the penetrant from entering the flaws, rendering the test ineffective for detecting them. The other methods listed are generally acceptable for removing organic and other contaminants without damaging the surface.
Question 3: When comparing Type I (Fluorescent) and Type II (Visible) liquid penetrant systems, which statement is generally correct regarding their sensitivity?
- Type II is more sensitive because the red dye has higher contrast under normal light.
- Type I is more sensitive because the human eye is more readily drawn to a glowing indication against a dark background. (Correct answer)
- Both types have equivalent sensitivity, and the choice is based only on lighting availability.
- Sensitivity is determined by the removal method (e.g., water-washable vs. solvent-removable), not the dye type.
Correct answer: Type I is more sensitive because the human eye is more readily drawn to a glowing indication against a dark background.
Type I (Fluorescent) penetrant systems are generally considered more sensitive than Type II (Visible) systems. The reason is that under proper UV-A (black light) conditions in a darkened area, the glowing fluorescent indication provides a much higher contrast against the dark background, making it easier for the human eye to detect very fine and small indications that might be missed with a visible dye.
Question 4: A technician is performing a solvent-removable visible dye penetrant test. During the excess penetrant removal step, the technician sprays the solvent remover directly onto the test surface before wiping. What is the most likely negative consequence of this action?
- It will be impossible to apply the developer afterward.
- It can flush the penetrant out of shallow discontinuities, leading to missed flaws. (Correct answer)
- It will cause the penetrant to dry too quickly, preventing it from entering flaws.
- It will create a chemical reaction that makes the developer non-absorbent.
Correct answer: It can flush the penetrant out of shallow discontinuities, leading to missed flaws.
For the solvent-removable method, the correct procedure is to apply the solvent to a lint-free cloth and then wipe the surface. Spraying the solvent directly onto the part is too aggressive and can wash the penetrant out of the discontinuities it is intended to find, especially shallow ones. This results in a high probability of failing to detect existing flaws.
Question 5: After completing a liquid penetrant inspection and evaluating the results, what is the critical final step in the process before returning the component to service?
- Applying a second coat of developer to confirm the indications.
- Post-cleaning the component to remove all inspection materials. (Correct answer)
- Heating the component to bake the developer into a permanent record.
- Documenting the results, as no further action is needed for the component itself.
Correct answer: Post-cleaning the component to remove all inspection materials.
Post-cleaning is a critical final step to thoroughly remove all residual penetrant and developer materials. If left on the surface, these chemicals can sometimes interfere with subsequent manufacturing processes (like welding or painting) or could potentially cause corrosion or other adverse effects on the component during service.
Question 6: During a liquid penetrant inspection, an inspector notes a large, fuzzy red indication on the developer. The indication does not have sharp, clear edges. Which of the following is a plausible cause for this type of indication?
- Insufficient penetrant dwell time was allowed.
- A very fine, tight crack is present.
- The developer was applied too thinly.
- Excessive penetrant was left on the surface before developer application. (Correct answer)
Correct answer: Excessive penetrant was left on the surface before developer application.
If excess penetrant is not properly removed from the surface, it will be absorbed by the developer along with the penetrant that bleeds out from a flaw. This leads to a large, fuzzy, and poorly defined indication with high background color, which can mask relevant discontinuities or be misinterpreted. Insufficient dwell time or a very tight crack would likely result in a very small or non-existent indication.
NDT - Non-Destructive Testing Liquid Penetrant Testing Process Questions and Answers
An NDT technician applies a visible dye penetrant to a non-porous component.
After the appropriate dwell time, the excess penetrant is removed, and a non-aqueous wet developer is applied.
Which of the following is the PRIMARY function of the developer in this process?