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Dye Penetrant Inspection

Dye penetrant inspection is an NDT method that is used to reveal surface breaking flaws by bleedout of a coloured or fluorescent dye from the flaw.

The technique is based on the ability of a liquid to be drawn into a "clean" surface-breaking flaw by capillary action. After a period of time called the "dwell", excess surface penetrant is removed and a developer applied. The developer acts as a "blotter". It draws out the penetrant from the flaw to reveal its presence on the surface. Colour contrast penetrants require good white light while fluorescent penetrants need to be used in controlled darkened conditions with an ultraviolet "black light".

Penetrant inspection can be used on any solid material. It is essential that the material is carefully cleaned first, otherwise the penetrant will not be able to get into the flaw. If surface penetrant is not fully removed, misleading indications will result.