PT

Dye Penetrant Testing (PT) is used to find surface breaking defects. PT inspection is suitable for a wide variety of materials, but it is mainly used on non-ferrous metals. This method makes use of the capillary action principle. A liquid dye with low viscosity is applied to the test piece. Due to its low viscosity, it gets sucked into surface-breaking discontinuities. After allowing adequate penetration time, the excess penetrant liquid is rinsed off. After drying, a chalk-like developer is applied. The developer draws the penetrant dye from defects making a visible indication that can be interpreted by the inspector.

High sensitivity to small surface discontinuities
Suitable for large range of materials: metallic and non-metallic, magnetic and non magnetic, and conductive and non-conductive
Large surface areas and large volumes parts can be inspected rapidly and at low cost
Parts with complex geometry can be tested without changing the inspection procedure
Indications are produced directly on the surface of the part
Aerosol spray cans make penetrant materials very portable
Required materials and equipment are relatively inexpensive

Only surface breaking defects can be detected
Only materials with relatively nonporous surface can be inspected
Precleaning is critical
Metal smearing from machining, grinding, and grit or vapor blasting must be removed prior to inspection.
Surface finish and roughness can affect inspection sensitivity
Multiple process operations must be performed with waiting intervals
Post cleaning of acceptable parts or materials is required
Handling and proper disposal of chemicals is required