Dye Penetrant testing (PT) is a Non-Destructive Testing technique in which the examiner uses a penetrating fluid to locate any defects which have an open connection to the surface. This can be done in daylight conditions with red penetrant or in a darkened room under ultraviolet light with fluorescent penetrant for a higher sensitivity.
With this type of inspection, it is very important that the surface is thoroughly cleaned before commencement; paint, grease and dirt must be removed, after which the penetrant liquid can be applied. Due to the capillary action between the liquid and the tested material the penetrant will be draw slowly into any defect. After the removal of the remaining penetrant, and the application of a developer, the defect will bleed out into the applied white developing powder causing an observable indication on the surface. The obtained indication can now be evaluated in accordance with the required standard.