Dye Penetrant Inspection

Liquid penetration inspection is a 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. This acts as a "blotter". It draws the penetrant from the flaw to reveal it's presence. Coloured (contrast) penetrants require good white light while fluorescent penetrants need to be used in darkened conditions with an ultraviolet "black light".

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