Dye Penetrant Testing

This test is named for the liquid, called penetrant that is applied to the sample during testing in order to make any surface flaws more visible.

A variety of penetrant materials are available and selection is often based on the required sensitivity level of the test, equipment available at the test site to conduct the test and other factors:

  The penetrant comes in two types of liquids-visible dye (colored red) and fluorescent dye (colored green-yellow).
  Fluorescent penetrants are also classified by sensitivity levels ranging from one through four, with four being the most sensitive for detecting the finest flaws.
  Penetrants can be washable with water, removable with a solvent or require treatment with an emulsifier that is lipophilic (oil-based) or hydrophilic (water-based).
  The liquid penetrant contains either a colored dye easily seen in white light, or a fluorescent dye visible under black (ultraviolet) light. The penetrant is applied by dipping, spraying, brushing, or flowing. After penetrant application, a sufficient time (dwell time) is provided to permit the penetrant to permeate the flaw.

The liquid penetrant can be examined by PT or FPT method, for the highest sensitivity a fluorescent Penetrant in combination with a black light is available. PT can only find surface breaking defects, needs a very thorough surface preparation and has a high sensitivity.