There
are various non-destructive testing techniques, but very few are
favourable for all types of applications. For example, for most composite
substances, applying electromagnetic testing methods will not work at all.
Still, if you go on with computed tomography & X-rays, they will be a perfect
choice!
- Porosity
- Seams
- Laps
- Fatigue Cracks
- Pin holes in welds
- Grinding cracks
- Quench cracks
- Absence of fusion/braising along the edge of the bond border
- Overload & consequence fractures
The Process Of Liquid Penetrant
Testing — Explained In 8 Simple Steps
1) Preparation Of The Surface
The first step in liquid penetrant testing is surface preparation. The material's surface must be free
of dirt, grease, oil, water, or additional contaminants that might restrict the
penetrant from seeping into the flawed material.
The
given testing material might also need etching if mechanical operations like
sanding, machining, or grit blasting have been conducted previously. These and
many other mechanical operations can actually coat or mark material over the
opening of the flaw and prevent the liquid from penetrating. The fluid is
applied to the surface of the material and penetrates into the crack of the
surface.
2) Application of the penetrant
After cleaning and drying the
material's surface, the penetrant must be applied by brushing, spraying, or immersing the part completely into the penetrant.
3) Letting The Penetrant Enter Into
The Material
After the second step, the penetrant is left on the material's surface
for a specific time to allow it to penetrate into the material. The penetrant
dwell time is the complete time given to the penetrant to seep into the surface
of the material.
The
penetrant manufacturers or the required specification decides the dwell time.
Here, the time might vary depending on the application, penetrant used, the sample
material, the form of the substance being examined, and the type of substance
being assessed for!
But
the maximum dwell time generally ranges from 30-60 minutes. Typically, there is
no disadvantage in utilizing a penetrant with a longer dwell time as long as
the penetrant is not permitted to dry up. However, the perfect & ideal
dwell time is actually specified by experiment and might be very specific to a
respective application. The surplus penetrant that is on the surface of the
piece must be rubbed out.
4) Removal Of Excess Penetrant
This is considered to be the
most delicate & important part of the entire examination process. This Is
so because the extra penetrant must be eliminated from the material's surface.
Depending on the penetrant utilized, this particular step might include
cleaning it by using a solvent, direct water rinsing, or treating the material
with an emulsifier & then rinsing it with water. The developer helps draw
out the penetrant trapped in the cracks so that it can be clearly visible to an
examiner.
5) Application Of The Developer
A layer of developer is
applied to the sample material. Various forms of developer might
be applied by spraying, dusting, or dipping.
6) Developer Time
In the sixth step, the
developer is made to sit on the material's surface for a specific time to allow
the extraction of penetrant out of any surface defects. The development time is
generally a minimum of 10 to 15 minutes.
7) Assessment
Next, a thorough examination
is conducted under proper lighting to identify the indications coming
from any defects which might be present in the substance.
8) Surface Cleaning
So the last step in this
whole process is to precisely clean the material's surface to eliminate the
developer from the parts of the material that were found to be admissible.
Advantages Of Liquid Penetrant
Testing
There
are a lot of advantages to using liquid penetrant testing. Some of them are mentioned below:
- Delivers clear, real-world
outcomes.
- Operates on complex geometric
structures.
- The liquid penetrant testing
materials are solely very cost-effective in nature.
- It is quite sensitive to
minor surface interruptions.
- The materials are compact.
Only a few material
limitations are there, such as works on metallic/non-metallic,
magnetic/non-magnetic, and conductive/non-conductive materials.
Disadvantages Of Liquid Penetrant
Testing
With
so many benefits, liquid penetrant testing has a few disadvantages also! Let's
check them out:
- The user is reliable.
- It is sensitive to
surface-breaking deformities.
- The testing procedure is
multi-purpose.
- Zero depth sizing.
- It's a time taking procedure
where post-cleaning of the material is very important.
- A direct connection to the
surface of the material under examination is significant.
- For progress in the
monitoring process, no recordable data can be attained.
- It only works on fairly
non-porous surface substances.
Therefore,
in absoluteness, despite the quick captivation of this cost-effective testing
method, it holds many downsides that must be looked into even before dismissing
more advanced and additional costly examination solutions, whether you accord
assessments or conduct them on yourself!

Key takeaways
Liquid penetrant testing is one of the most commonly utilized non-destructive testing techniques. The material
& procedures that are utilized in the liquid penetrant testing are
developed to create the outcomes of this capillary activity and the ability of
interpretation. Liquid penetrant testing is an adequate way of uncovering and
specifying the stringency of surface flaws in the materials, including those
that are not visible to the eye.
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