FAA Aviation Mechanic General (AMG)Materials, Hardware and ProcessesHard
A technician performs a liquid penetrant inspection on a suspect crankshaft. After removing excess penetrant from the surface, the technician skips directly to inspection under white light without applying the next required step. What is the most likely consequence?
- AFine surface cracks may not become visible because the developer is needed to draw penetrant out of the flaw
- BThe part will show false positive indications everywhere
- CThe penetrant will not adhere properly to the surface
- DThe dwell time will be extended unnecessarily
Show answer & explanationAnswer & explanation
Correct answer: A. Fine surface cracks may not become visible because the developer is needed to draw penetrant out of the flaw
After excess penetrant is removed, a developer must be applied to blot penetrant trapped in surface discontinuities back up to the surface, creating a visible indication. Skipping this step can cause fine cracks to go undetected since the small amount of penetrant remaining in the flaw may not be visible without the developer's wicking action.
Why the other options are wrong
- B. Omitting developer causes missed indications, not false positives.
- C. Penetrant adhesion occurs before excess removal, unrelated to this step.
- D. Dwell time refers to penetrant soak time, which occurs earlier in the process.
Liquid Penetrant Inspection (LPI)
A nondestructive testing method that reveals surface-breaking defects by applying penetrant, removing excess, then applying developer to draw the penetrant back out for visibility.
- Works on nonporous ferrous and nonferrous materials
- Steps: clean, apply penetrant, dwell, remove excess, apply developer, inspect
- Developer is critical to reveal fine surface cracks
Memory trick: 'Clean, Color, Wait, Wipe, Powder, Peek'