Liquid Penetrant Inspection requires the test object or material to be thoroughly precleaned and free of paint, grease and loose debris.
The test area is then coated with a visible or fluorescent dye solution which is allowed to “soak” into open surface flaws.
After a suitable dwell time, the excess dye is removed from the surface and a developer which draws out the dye solution out of imperfections open to the surface is applied. With visible dyes, the vivid colour contrast between the penetrant and the developer is used to highlight any flaws. With fluorescent dyes, an ultraviolet “black light” lamp is used to contrast the “bleed out” and fluoresce brightly, allowing the imperfection to be seen readily.