Liquid Penetration Inspection

This method is used to detect large cracks or openings, cold shuts, fatigue cracks and pits. There are two types of liquid penetration inspections.

• Dye penetration inspection.
• Fluorescent liquid penetration inspection.

Dye penetration inspection

The liquid Dye penetrant is sprayed on to the clean surface of test piece. Excess amount of Dye is removed; surface is washed with water and thoroughly dried. Then a developer is sprayed on surface, which brings out the colour in the dye penetrant that has penetrated into cracks or pinholes.

Fluorescent liquid penetration inspection

Fluorescent liquid is applied to the surface to be inspected. After removing the excess liquid, surface is washed and dried. Then the test surface is viewed under black light whose wavelength lies between the visible and ultra violet regions of the spectrum, which causes penetrant to glow clearly in the dark. Some solids used in the cleaners and developers contain a high percentage of chlorine to make the liquid non-inflammable, but requires a great care in view of health hazards associated with chlorine. Penetrant testing has the benefit that it might be used for all types of materials.