Penetrant wash parameters

Removal is the step that decides whether a penetrant examination works. The object is to strip the penetrant from the surface while leaving it undisturbed in the discontinuity, and the only thing separating those two outcomes is how much mechanical and thermal energy the rinse delivers.

Pressure supplies the mechanical energy. A coarse spray at low pressure lifts the surface film by wetting and flow; a jet at high pressure drives water into the discontinuity and flushes the penetrant straight out of it, particularly from shallow, wide, service-induced defects. The limit is 275 kPa (40 psi), applied as a coarse spray from a distance, never as a focused jet held close to the surface.

Temperature supplies the thermal energy and changes the penetrant's own properties. Hot water thins the penetrant and increases its solubility in the remover, so removal accelerates in the flaw as well as on the surface; cold water leaves a stubborn film that the operator then over-rinses to clear, which produces the same damage by a different route. The working band is 10 to 40 °C (50 to 100 °F).

Not every technique may be water washed. Solvent removable penetrant (Method C) is removed by wiping with a clean, dry lint-free cloth and then with a cloth lightly dampened with solvent - never by flooding or spraying solvent onto the part, which will strip the discontinuities exactly as an over-pressure rinse would. Post-emulsifiable penetrants may only be rinsed after the emulsifier has done its work, and the rinse is what stops the emulsification clock.

Maximum rinse water pressure: 275 kPa (40 psi)
Rinse water temperature: 10 to 40 °C (50 to 100 °F)
Pressure margin = 275 kPa - measured pressure
Solvent removable (Method C): no water wash - wipe with a lightly dampened lint-free cloth