DYE PENETRANT TEST
1. Advantages
High sensitivity to small surface discontinuities
Easy inspection of parts with complex shapes
Quick and inexpensive inspection of large areas and large volumes of parts/materials
Few material limitations (metallic and nonmetallic, magnetic and nonmagnetic, and conductive
and non-conductive can all be inspected)
A visual representation of the flaw are indicated directly on the part surface
Aerosol spray cans make the process portable, convenient, and inexpensive
Indications can reveal relative size, shape, and depth of the flaw
It is easy and requires minimal amount of training
2. Disadvantages
Detects flaws only open to the surface
Materials with porous surfaces cannot be examined using this process
Only clean, smooth surfaces can be inspected. (Rust, dirt, paint, oil and grease must be
removed.)
Metal smearing from power wire brushing, shot blasting, or grit blasting must be removed prior
to liquid penetrant examination
Examiner must have direct access to surface being examined
Surface finish and roughness can affect examination sensitivity. (It may be necessary to grind
surfaces before PT.)
Multiple process steps must be performed and controlled
Post cleaning of parts and material is required, especially if welding is to be performed
Proper handling and disposal of chemicals is required
Fumes can be hazardous and flammable without proper ventilation
It is important to remember penetration is a very thin liquid designed to seep into the smallest crack.
Consequently, if an assembly has stitch welds or material not sealed by a weld, the penetration will
travel behind the welds and between layers of unused material. Penetration can be nearly impossible to
remove from these areas. Trapped penetration will cause defects in welds if further welding is done or
will bleed out over time and contaminate paint and process fluids.
For PT to be used on ASME Code construction or NBIC repair or alterations, a written procedure must be
followed. This must comply with ASME Boiler and Pressure Vessel Code, Section V, Article 6, and address
all essential and nonessential variables. Many liquid penetration examinations are done for
informational purposes only, and do not follow a written procedure. For instance, a written procedure
does not need to be followed if a welder grinding out a weld crack for repair is using PT to ensure
removal of the entire crack. However, if the PT is being done to comply with Code, the written
procedure needs to be followed by qualified NDE personnel.
There are six basic steps to follow when using the dye penetration solvent removable method.
DYE PENETRANT TEST
3. Pr-clean part.
This can range from grinding and wire brushing to merely wiping the part with a rag moistened
with the cleaner/ remover. The surface needs to be free of dirt, rust, scale, paint, oil, and
grease, and be smooth enough to wipe off the penetration without leaving residue.
4. Apply penetrant.
This is generally done by spraying penetrant from the aerosol can or applying it with a brush. A
dwell (soak) time needs to be observed to allow for the penetrant to permeate into cracks and
voids. This is typically 5 to 30 minutes but should never be long enough for the penetrant to
dry. The penetrant manufacturer’s recommendations and written procedure should be
followed.
DYE PENETRANT TEST
5. Remove penetrant
All penetrant should be removed with clean, dry, lint-free rags until thoroughly clean. The part
or material should be rubbed vigorously until the penetrant is not visible on the dry rags.
Next, cleaner/ remover should be sprayed on another clean, dry, lint-free rag and used to
vigorously rub the part again until there is no penetrant visible on the rag.
6. Apply developer
A thin, light coating of developer should be sprayed on the part being examined. A dwell time
needs to be observed to allow time for the dye to exit the flaws and create an indication (flaw)
in the developer. The dwell time for developer is typically 10 to 60 minutes. The developer
manufacturer’s recommendations and written procedure should be followed closely.
7. Evaluate indications
DYE PENETRANT TEST
It is critical to examine the part within the time frame designated in the written procedure.
Length of an indication can grow over time as penetrant bleeds out, causing an acceptable
indication to be a rejectable defect. Length of indication is measured for evaluation, not length
of the flaw. Here, the two linear indications are rejectable defects. The round indication
is nonrelevant.
8. Post-clean part
The part needs to be cleaned to remove all developer after it has been evaluated.
