Dye Penetrant Inspection (DPI) also called as Liquid Penetrant Inspection (LPI) or Penetrant Test (PT) is fast, economical and widely used nondestructive test method to detect surface-breaking discontinuities in all non-porous materials (metals, plastics, or ceramics).
Penetrant test is based upon the principles of capillary action where liquid penetrates into a cavity.
Penetrant test is performed by cleaning the test surface thoroughly, applying colored or fluorescent penetrant, and allowing penetration time, removal of excess penetrant followed by application of developer (dry or liquid form).
The developer assists to draw penetrant out from the surface breaking discontinuities.
After developer dwelling the test surface is examined for bleed out under natural light or black (UV) light (depending on the type of penetrant).
Fluorescent Dye Penetrant Inspection (FDPI) is the most sensitive test method.
Dye penetrant Inspection (DPI) is predominantly used on non-ferrous materials in aerospace industries, shipping and offshore, petrochemical industries and stainless industry.
Some of the common parts tested are stainless steel welded joints, aluminum alloys joints, turbine blades, stainless steel fittings, castings and forgings, weld overlays (satellite), aerospace engine parts, etc.