Dye Penetrant Testing

We provide single and serial testing of your components for surface defects with dye penetrant testing

Non destructive testing with dye penetrant testing (PT)

What is dye penetrant testing?

Dye penetrant testing (PT), also called red-white testing, is a surface crack detection method. It is suitable for testing surfaces for defects in almost all materials and is widely used in industry.

How does dye penetrant testing work?

Surface inspection by means of dye penetrant testing makes use of the capillary effect. The capillary effect describes the behavior of liquids in contact with capillaries, e.g. in contact with tubes, cracks, cavities, notches and scratches. Due to an interaction of the surface tension of liquids and materials, a liquid is also drawn into such capillaries by gravity. An everyday example of the capillary effect would be, for example, the absorption of water by a sponge or the rising of water in a straw.

Step 01

Prepare material

The first step is to carefully clean and degrease the surface of the component to be tested so that the flaws are open to the surface without interruption.

Step 02

Spray on dye penetrant:

Then spray the surface with the intensely red colored or fluorescent dye penetrant. Due to the capillary effect, the dye penetrates into the defective areas of the component.

Step 03

Removing the dye penetrant

After a certain exposure time, the dye penetrant is carefully removed from the surface, for example with water or a system cleaner, and the component is dried.

Step 04

Spray on developer

In the next step, a white developer is sprayed on. The red penetrant “bleeds” from the defects, making them visible. If fluorescent dye penetrant is used, defects are made visible by irradiation with UV light.

When is dye penetrant testing used? 

Dye penetrant inspection is used to detect defects on the surface of the material.

Detectable defects are:

  • Cracks
  • Notches
  • Surface shrinkage cavities

Special requirements:

  • The defect must be open to the surface
  • The material to be tested should not be porous
  • The surface of the material must be clean and free of grease
  • Smallest detectable flaw:
    From 0.01 mm

Detectable defect location:

Surface defect


* The specifications depend on the geometry and physical properties of the material to be tested and are therefore only intended as a guideline.

Dye penetrant testing with VOGT Ultrasonics

We test your components either single or in series in our VOGT test center in Burgwedel (Hanover) or directly at your site.

(Bild) Zerstörungsfreie Prüfung mittels der Farbeindringprüfung (PT) an Kugeln

Application examples

(Bild) Zerstörungsfreie Prüfung mittels der Farbeindringprüfung (PT) an Bauteilaufnahmen einer Maschine

Non destructive testing by dye penetrant testing (PT) of component fixtures of a machine

(Bild) Zerstörungsfreie Prüfung mittels der Farbeindringprüfung (PT) an einer Vorderradaufhängung eines Passagierflugzeuges

PT Testing the front suspension of a passenger aircraft

(Bild) PT-Prüfung am Windflügel eines großen Windkanals. Es zeigen sich ausblutende Anzeigen der Oberflächenporigkeit, jedoch keine Belastungsrisse.

PT on the wind vane of a large wind tunnel. There are bleeding indications of surface porosity, but no stress cracks.