Fluorescent Penetrant Inspection (FPI)
What Is Fluorescent Penetrant Inspection (FPI)?
Fluorescent Penetrant Inspection (FPI), also known as Dye Penetrant Inspection (DPI) using fluorescent dye, is a non-destructive testing (NDT) method used to detect surface-open discontinuities such as cracks, porosity, laps, seams, and cold shuts.
-
Suitable for non-porous materials such as metals, plastics, ceramics, and glass
-
Provides high sensitivity to fine surface defects
-
Fluorescent dye glows under UV light for clear defect visibility
Principle of FPI
Fluorescent Penetrant Inspection works on the principle of capillary action:
-
Liquid penetrant is applied to the clean test surface.
-
Penetrant enters surface-open defects through capillary action.
-
Excess penetrant is removed after the required dwell time.
-
A developer draws penetrant out of surface flaws.
-
Under ultraviolet (UV) light, the fluorescent dye glows and reveals defects.
This method detects only surface-breaking defects and does not identify subsurface flaws.
Typical Applications
-
Aerospace – turbine blades, landing gear, fasteners
-
Automotive – engine components and gears
-
Manufacturing – welds, castings, and forgings
-
Railway & Shipbuilding – structural components
-
Power generation – shafts, rotors, and valves