Which statement is not a basic principle of penetrant inspection?

Which statement is not a basic principle of penetrant inspection?

• A. Indications glow when illuminated with a black light
• B. Penetrant indications are visible only after proper developer is applied
• C. The technique requires surface cleanliness prior to penetrant application
• D. Indications appear on the surface in the vicinity of discontinuities

Answer: (A)

Penetrant inspection rests on how the surface is prepared, how the penetrant is allowed to enter defects, and how indications are revealed and observed under the proper lighting. The indented areas where defects exist become visible because the penetrant stain is drawn out by the developer and then seen under the appropriate illumination, not because of any inherent “glow” in every case. The statement about indications glowing when illuminated with a black light isn’t a universal principle because visibility depends on the type of penetrant used and the lighting condition. You can use either visible penetrants viewed under white light or fluorescent penetrants viewed under ultraviolet light; the crucial idea is that indications are observable with the correct illumination for the chosen penetrant, not that they must glow under a black light in all situations. In contrast, the other points describe essential steps: you must have a clean surface, you must allow dwell time for the penetrant to enter flaws, a developer must be applied to reveal the indications, and the indications appear at or near the discontinuities.

Penetrant inspection rests on how the surface is prepared, how the penetrant is allowed to enter defects, and how indications are revealed and observed under the proper lighting. The indented areas where defects exist become visible because the penetrant stain is drawn out by the developer and then seen under the appropriate illumination, not because of any inherent “glow” in every case.

The statement about indications glowing when illuminated with a black light isn’t a universal principle because visibility depends on the type of penetrant used and the lighting condition. You can use either visible penetrants viewed under white light or fluorescent penetrants viewed under ultraviolet light; the crucial idea is that indications are observable with the correct illumination for the chosen penetrant, not that they must glow under a black light in all situations. In contrast, the other points describe essential steps: you must have a clean surface, you must allow dwell time for the penetrant to enter flaws, a developer must be applied to reveal the indications, and the indications appear at or near the discontinuities.