What is Liquid Penetrant Testing

What is Liquid Penetrant Testing


The principle of liquid penetrant testing (PT) is based on capillary action of liquids whereby the penetrant applied on the surface enters the discontinuities and shows them visibly on the surface.


Equipment includes a cleaner, penetrant and developer. Penetrants will either include a visible dye or a fluorescent dye. A developer  is a medium that is applied to pull the penetrant out of the discontinuities and also provide a white background. Ultraviolet light source, light meter. TAM panel for aerospace work.


Liquid penetrant testing is widely used in aerospace, power and manufacturing industries for surface inspections. The method is applicable to non-porous material such as metals. Field inspections are done using spray cans. In-house assembly line inspection are done using tanks with spray and dusting stations.  Steps for penetrant testing include:

  1. Clean the surface
  2. Apply penetrant – visible or fluorescent
  3. Dwell time – wait for the penetrant to soak in. About 5 to 10 minutes
  4. Remove penetrant using solvent, water or emulsifiers
  5. Apply developer and observe any discontinuities that appear
  6. Inspect and report


Level II – NDT-103
Duration – 16 hours

NAS410 Level II Course No – NDT-109
Duration – 32 hours