What is Dye Penetrant Testing (PT)?
Dye penetrant testing (PT) is a surface inspection method that shows cracks open to the surface of a nonporous part.
How it works
Inspectors use the method on nonporous metal and nonmetal parts. It finds flaws that are open to the surface and may not show in normal visual inspection. The part must be clean first.
- The inspector applies a liquid with high penetrating power. It enters the surface opening of a flaw.
- The inspector removes the excess penetrant.
- The inspector applies a developer. It draws the liquid out of the flaw.
- The flaw shows as a color contrast in white light, or as fluorescence under ultraviolet light.
Types
FAA AC 43.13-1B classifies penetrant materials by dye type, by removal method and by sensitivity level.
- Type: Type I is fluorescent dye, Type II is visible dye, and Type III is both (dual mode).
- Removal method: water washable, post-emulsifiable (two kinds) or solvent removable.
- Sensitivity level: five levels, from ultralow to ultrahigh.
Limits
- The method finds only flaws that are open to the surface.
- Surface roughness or porosity can cause excessive background indications.
- The FAA says the method is better than visual inspection, but not as sensitive as other advanced tests for in-service surface cracks.
Standards
AC 43.13-1B names MIL-I-25135E for penetrant materials, MIL-STD-6866 for the minimum process requirements and ASTM E1417. Its Table 5-6 also lists ASTM E165.
Airfield use
None of the airfield documents that we checked describe this test for lights or pavement. TarmacView does not offer it.
Frequently Asked Questions
- What does dye penetrant testing find?
- It finds flaws that are open to the surface of a nonporous metal or nonmetal part and are hard to see in normal visual inspection. It cannot find flaws below the surface. Another method must find those.
- Does dye penetrant testing work on rough or porous surfaces?
- Not well. Surface roughness or porosity can cause excessive background indications that interfere with the inspection. The method is meant for nonporous parts.
- Is fluorescent penetrant better than visible dye?
- For small surface cracks on propeller blades, yes. FAA AC 20-37E says fluorescent penetrant is far superior to visible dye and does not recommend visible dye for propellers.
- How is dye penetrant testing different from magnetic particle inspection?
- Penetrant testing does not need a ferromagnetic part. It works on nonmagnetic metals and on many nonmetals. Magnetic particle inspection works only on iron and steel, and it can also find slightly subsurface flaws.
References
This is a reference entry. TarmacView provides drone inspection services and doesn't sell the equipment or materials described in this glossary.
