Dye-penetrant test

The penetrant test or fluorescent penetrant inspection is a non-destructive method used to detect surface cracks (see Crack) and pores in metal and non-metal workpieces according to EN 571-1 (penetrant testing and execution), EN 3452-2 (penetrant testing; testing of penetrant materials) and 3 (reference test blocks and their use for determining and classifying the sensitivity of testing agent systems).

The non-porous cleaned surface is wetted with a dyed or fluorescent contrast medium penetrating into the finest cracks due to capillary action. Afterwards, the workpiece surface is cleaned. Fluorescent penetrant remaining in recesses formed by cracks or pores becomes visible under UV light.

Fig. 1 shows a schematic representation of the penetrant test method. When using dye-based penetrants, a so-called developer is applied which has a high color contrast to the penetrant, making the contrast medium remaining in the recesses visible. The entire test procedure includes cleaning of the workpiece, wetting with penetrant, applying the developer, if required, and visually inspecting the workpiece.

The dye-penetrant test is a method used for the full inspection of function- and safety-critical components which are made of metal materials, such as steel or aluminum, or non-metal materials having a porous surface, such as ceramic. The method is particularly suitable for workpieces with a complex and irregular geometry. For unmachined surfaces, surface roughness should not exceed a value of 30% of the crack depth. The method provides about the same accuracy as the magnetic particle inspection, but is also suitable for non-magnetic materials.

Additional references:
Crack detection
Magnet particle inspection
Capillary crack, Hardening crack, Hot crack, Cold crack, Warm crack

  • Fig. 1: Dye-penetrant test (source: Wikipedia)1. Cleaning2. Applying dye and waiting for it to penetrate into the specimen3. Cleaning the surface4. Applying developer
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