Dye penetrant inspection (PT) is a widely applied and low-cost inspection method used to locate surface breaking flaws. To be detected, the flaw must reach the surface to be tested. Dye penetrant (PT) can be applied to both ferrous and non-ferrous materials and all non-porous materials.
PT is used to detect cracks, surface porosity, lack of penetration in welds and defects resulting from in-service conditions, such as fatigue cracks of components or welds, in castings, forgings and weldments. The dye penetrant in drawn into the surface-breaking crack by capillary action and excess surface penetrant is then removed. A developer is then applied to the surface to draw out the penetrant in the crack and produce a surface indication. Cracks as narrow as 150 nanometers can be detected.
This method of NDT is useful for testing on-site as it is portable, and when applying certain techniques such as visible colour contrast there is no need for additional resources such as electricity or water.
Penetrants are classified by their sensitivity levels and, when selecting a penetrant, factors such as environment under which the test is to be performed, surface finish and the size of defects are considered.
