Penetrant
Dye penetrants are creep-capable liquids applied to the cleaned surface during penetrant testing. They penetrate into the finest cracks by capillary forces and allow visual inspection of surface integrity.
Physical-Chemical Mechanism of Action
Dye penetrants are liquids that can penetrate fine cracks due to their creeping properties. This happens through capillary forces, where the liquid element expands on the surfaces of solids and moves into the cracks.
Metallurgical Relevance & Risks in Welding
Penetrant testing with dye penetrants is an important tool for checking surface integrity. It can reveal fine cracks or contaminants that are not visible by optical methods. Insufficient surface cleaning can lead to false positive results, as the penetrant also enters fine contaminants.
Workshop Practice & Instructions
Before penetrant testing, the surface must be thoroughly cleaned. This can be done with chemical cleaners or mechanical methods like grinding or polishing machines. The dye penetrant is then applied to the cleaned surface and wiped off after a certain time (usually 5-10 minutes). The surface is then examined under light to detect fine cracks or contaminants. It is important that the penetrant does not enter broad cracks, as this can make the test inaccurate.