Liquid Penetrant Inspection (LPI) Level 1 Practice Test

Which surface condition is explicitly mentioned as potentially detrimental to liquid penetrant testing?

A perfectly dry surface A polished surface A painted surface A wet surface

Correct Answer:

A wet surface

Explanation:

Moisture on the surface disrupts the penetrant process. Liquid penetrant testing relies on the penetrant entering surface-breaking defects by capillary action, which works best when the surface is clean and dry. A wet surface introduces a water film that can prevent proper wetting of the defect, dilute or wash away penetrant, and interfere with the subsequent development and inspection steps. This reduces the test’s sensitivity and can mask defects or produce unreliable indications. A perfectly dry surface is what you want for good penetration; a polished or painted surface isn’t inherently described as detrimental in this context, whereas a wet surface is, which is why the correct choice points to moisture being harmful.

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