What is DPI?
What is DPI?
Dye Penetrant Inspection (DPI), sometimes called Liquid Penetrant Inspection (LPI) or Penetrant Testing (PT), is a simple low-cost NDT method used to locate surface-breaking defects in all non-porous materials. DPI can be used on both ferrous and non-ferrous materials - Although for ferrous components MPI normally used instead for its subsurface detection capability.
Why use DPI?
- Suitable for non-ferrous components - Not limited to metals
- Easy Inspection of components with complex shape
- High sensitivity - Indications can reveal relative size, shape, and depth of the flaw
- Ideal for crack testing - Especially weld testing
- Aerosol spray cans make the process portable and convenient
- Easy to understand and requires minimal training
- Well-established method of NDT
- Quick and inexpensive - Inspect large areas and large volumes of components
DPI works by capillary action, where low surface tension fluid ‘penetrates’ into clean and dry surface-breaking discontinuities. Penetrant is typically applied to a test component by dipping, spraying, or brushing.
After adequate penetration time (dwell time) has been allowed, the excess penetrant is removed and a developer is applied. The developer helps to draw penetrant out of the flaw so that an invisible indication becomes visible to the inspector.