DPI - how does it work?

The Dye Penetrant Testing process is based on the ability of a liquid to be drawn into a surface-breaking flaw by capillary action. The first step is to clean the component that is being tested before applying the penetrant. Then a visible or fluorescent dye that is either water or solvent-based is then applied to the surface of the component by a variety of applications including spraying, brushing, dipping or full immersion of the component into the penetrant dye. During the penetration time, or dwell time, the coloured dye penetrates any surface breaking flaws that might exist in the component through capillary action. The length of the penetration time depends on the dye or penetrant that is being used. Any excess penetrant is then removed from the surface of the tested component before it is dried. A developing agent is then applied. The developing agent draws the penetrant out of any surface breaking flaws and onto the surface in a reverse process of capillary action. This forms a visible indication that reveals any flaws in the component ready for a visual inspection and reporting. Our inspectors then perform a visual inspection using either white light or ultraviolet light depending on the type of penetrant that was used.

For more information on DPI - how does it work? talk to Capital NDT Limited