Glossary

Dye Penetrant Testing (PT) is a non-destructive testing (NDT) method used to reveal surface-breaking flaws such as cracks, seams, laps, porosity, and leaks in both metallic and non-metallic materials. It works on any non-porous material—including metals, plastics, ceramics, and composites—making it more versatile than magnetic particle testing. The process begins with careful surface preparation to remove dirt, grease, paint, or other contaminants that could block the penetrant. A liquid dye, usually either visible red or fluorescent under ultraviolet light, is applied to the cleaned surface and allowed to dwell long enough to seep into any open defects by capillary action.

After the dwell time, excess penetrant is carefully cleaned from the surface while ensuring the dye remains inside the cracks or pores. A white developer is then applied, which acts like a blotter by drawing the trapped dye back out of the flaws, creating a strong contrast between the flaw indication and the background. Under proper lighting—white light for visible dyes or UV light for fluorescent penetrants—inspectors can see the indications clearly and evaluate the location, size, and nature of the discontinuities. PT is widely used across aerospace, automotive, energy, and manufacturing industries for inspecting welds, castings, forgings, and machined parts. While it is sensitive, inexpensive, and easy to apply, PT is limited to detecting only surface-breaking flaws, requires thorough cleaning before and after testing, and depends heavily on inspector skill for accurate interpretation.