Penetrant Testing (PT)

Dye Penetrant Testing (PT) is used to find surface breaking defects. PT inspection is suitable for a wide variety of materials, but it is mainly used on non-ferrous metals. This method makes use of the capillary action principle. A liquid dye with low viscosity is applied to the test piece. Due to its low viscosity, it gets sucked into surface-breaking discontinuities. After allowing adequate penetration time, the excess penetrant liquid is rinsed off. After drying, a chalk-like developer is applied. The developer draws the penetrant dye from defects making a visible indication that can be interpreted by the inspector.

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PT advantages:

  • High sensitivity to small surface discontinuities
  • Suitable for large range of materials: metallic and non-metallic, magnetic and non-magnetic, and conductive and non-conductive
  • Large surface areas and large volumes parts can be inspected rapidly and at low cost
  • Parts with complex geometry can be tested without changing the inspection procedure
  • Indications are produced directly on the surface of the part
  • Aerosol spray cans make penetrant materials very portable
  • Required materials and equipment are relatively inexpensive

PT limitations:

  • Only surface breaking defects can be detected
  • Only materials with relatively nonporous surface can be inspected
  • Precleaning is critical
  • Metal smearing from machining, grinding, and grit or vapor blasting must be removed prior to inspection.
  • Surface finish and roughness can affect inspection sensitivity
  • Multiple process operations must be performed with waiting intervals
  • Post cleaning of acceptable parts or materials is required
  • Handling and proper disposal of chemicals is required
Case Schelde Exotech

Unique NDT methods on riser forgings

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Henk Schroots

Area Sales Manager NDT & Laboratory
+31 (0) 6 49 35 78 02

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