What is Penetrant Testing? (PT)

What is Penetrant Testing?

Penetrant, or Capillary Liquid Testing, is a non-destructive testing method used to detect flaws that extend to the surface of non-porous materials. Such flaws could be cracks, porosities, gaps, and leaks in steel, cast iron, plastic, ceramic, etc.
A penetrant fluid, which is either colored or fluorescent, is applied to the cleaned surface of the test piece. This fluid penetrates even very small surface flaws through capillary action. Excess penetrant is removed from the surface, and after applying a developer fluid, the flaw can either be seen directly or under ultraviolet light.

See Penetrant Products

The History of Penetrant Testing:

Historically, a slurry of chalk mixed with alcohol was used, or—in cases with hot surfaces—mixed with water.

The surface to be inspected for cracks, etc., was first smeared with kerosene and then cleaned again, followed by applying the chalk/alcohol solution.

When the medium in suspension evaporated, the dried layer of chalk remained, and any cracks were visible as dark petroleum streaks on the white chalk surface.

This method has evolved into today’s Penetrant Testing (Capillary Liquid Testing), in which kerosene is replaced with a capillary dye, and the chalk/alcohol solution is replaced by a developer. Both are available, for example, in aerosol cans.

Additionally, special cleaning fluids have been developed, also available in aerosol cans. A Penetrant Set of this kind is, of course, available in our shop.

The advantage of storing the fluids in aerosol cans is that one has reasonably good assurance of always having clean and uncontaminated fluids available.

The method does not require a large investment, and the cans are easy to transport and take up little space during testing. However, the operator must be quite careful to carry out all steps correctly.

The capillary method is relatively slow when examining larger areas, whereas it can be very fast for serial production of smaller items. In that situation, the method can be automated by using baths of fluids and transporting items on a conveyor through the various baths, which can be further optimized by using ultrasonic baths. Only the final inspection for flaws is done manually, and even this can be automated with optical pattern recognition.