Penetrant

Dye penetrant testing examines the surface of an item for surface-breaking flaws, such as cracks or porosity by bleed out of a colored or fluorescent dye from the flaw. Penetrant is applied to the surface and left to dwell (seep) where the liquid is drawn into any cracks by capillary action. After the dwell time has expired, the excess penetrant is removed and a developer is applied by method of spraying, dusting, or dipping. The developer acts as a blotter and draws the penetrant from the flaw to the surface by reverse capillary action, resulting in a colored indication on the surface that is broader than the actual flaw, and therefore, much more visible. This technique can be used to detect surface flaws on almost any material provided that it is not rough or porous. Typical flaws detected are:

 

Grinding cracks

Heat zone cracks

Poor weld penetrations

Heat Treatment cracks

Fatigue cracks

Laminations

Micro shrinkage

Hot tears

Cold shuts

Stress corrosion cracks

Intergranular corrosion