Dye or liquid penetrant testing (PT or LPI) is used to inspect parts and weldments for open to surface discontinuities.

A penetrant solution is applied to a clean, bare surface and allowed to dwell for a certain amount of time. This allows the penetrant to be drawn into tiny cracks and other discontinuities that are of interest to the inspector.

This method is done in accordance with the following standards:

  • ASTM E165
  • CSA W59
  • ASME Section 5, Article 6

PT can be performed using visible or fluorescent dyes, and is available in a wide variety of sensitivity levels.

This method is often used to detect flaws that break to the surface, some of which can include:

  • Fatigue cracks
  • Quench cracks
  • Grinding cracks
  • Porosity
  • Laps
  • Seams
  • Pin holes in welds

Liquid dye penetrant testing (LPI) is an excellent method for finding surface breaking discontinuities in non-ferrous welds and materials.


Visible dye method.



Wet fluorescent method.

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