Liquid Penetrant Testing is widely used to find leaks in materials, such as metals, plastic and ceramics. This technique uses a liquid to be drawn into a clean surface breaking flaw by capillary action. After a period of time called the “dwell” excess surface penetrant is removed and a developer applied. This acts as a blotter.  It draws the penetrant from the flaw to reveal its presence.


  • Highly sensitive to small surface crack and flaws.
  • Very little equipment is needed
  • Large areas can be inspected quickly and at low cost.
  • Parts with complex shapes are inspected routinely.
  • Aerosol spray cans make penetrant materials very portable.
  • Low cost method


  • Only surface breaking defects can be detected.
  • Only areas with nonporous surfaces can be inspected.
  • Pre-cleaning is necessary as contaminants can mask defects.
  • The inspector must have direct access to the surface being inspected.
  • Surface roughness can affect inspection sensitivity.
  • Proper disposal is required.