Penetrant Testing · Theory
Why does penetrant need dwell time?
Nothing pushes penetrant into a crack. The liquid wets the crack walls and pulls itself in — that's capillary action, and it takes time.
- Spray the penetrant across the part, then watch it wick into the two cracks.
- The shallow crack fills quickly. The deep, tight one keeps drawing penetrant for minutes.
- You decide when to wipe off the excess. The procedure calls for a 10-minute dwell — see what happens if you cut it short.
- Then spray the developer and watch what's trapped in each crack bleed back out.