Liquid penetrate inspection is a non-destructive testing method used to identify surface-breaking defects. It works by applying a liquid penetrate that is drawn into defects via capillary action. Excess penetrate is removed and a developer is applied to pull trapped penetrate back to the surface, making defects visible. The process involves cleaning, applying penetrate, removing excess, applying developer, inspecting visually, and post-cleaning. Penetrate selection depends on the material and desired sensitivity level. Proper surface preparation, dwell time, and each step is important to obtain reliable results.

1. Liquid penetrate inspection
Unit-1
K.KRISHNA KISHORE
kakarlakishore11@gmail.com

2. • Liquid penetrate inspection:
• Principles of penetrate inspection,
• characteristics of a penetrate,
• water washable system,
• post emulsification system ,
• solvent removable system,
• surface preparation and cleaning,
• penetrate application,
• development,
• advantages limitations,
• and applications.

4. Principle
• The principle of the technique is that a liquid is
drawn by capillary attraction into the defect and,
after subsequent development, any surface-breaking
defects may be rendered visible to the human eye.

5. Introduction
• A liquid with high surface wetting characteristics is applied
to the surface of a component under test.
• The penetrant “penetrates” into surface breaking
discontinuities via capillary action and other mechanisms.
• Excess penetrant is removed from the surface and a
developer is applied to pull trapped penetrant back the
surface.
• With good inspection technique, visual indications of any
discontinuities present become apparent.

6. Basic Process
• 1) Clean & Dry Component
• 2) Apply Penetrant

7. 3) Remove Excess 4) Apply Developer
5) Visual Inspection
6) Post Clean Component

8. What Can Be Inspected
• Almost any material that has a relatively smooth, non-porous surface on
which discontinuities or defects are suspected.

9. What Can NOT be Inspected
• Components with rough surfaces, such as sand castings, that
trap and hold penetrant
• Porous ceramics
• Wood and other fibrous materials
• Plastic parts that absorb or react with the penetrant
materials
• Components with coatings that prevent penetrants from
entering defects

10. Choices of Penetrant Materials
• Penetrant Type
I Fluorescent
II Visible
Method
• Water Washable
• Post emulsifiable
• Solvent Removable

11. Visible Vs Fluorescent
• Visible Penetrate test is
performed under white light
• level 1 sensitivity range
Photo Courtesy of Contesco
•while fluorescent Penetrate test
must be performed using an
ultraviolet light in a darkened area
•Sensitivity ranges from 1 to 4
Fluorescent Penetrate test is more sensitive than visible Penetrate test
because the eye is more sensitive to a bright indication on a dark
background.

12. Characteristics Of A Penetrate
• Penetration
– The penetrant must have the ability to enter extremely fine surface defects or
other openings in the component under test.
• Body
– The penetrant must have a good surface wetting ability
• Fluidity
– the penetrant should have the ability to drain away from the
component well
• Solution ability
– If necessary, the penetrant should be capable of dissolving a path into
contaminated defects, through a wide range of contaminants.

13. • Stability
– The liquid penetrant should be stable over a wide range of
temperature and humidity
– should not form a *scum or lose its **volatile constituents while it is
kept in open tanks or when stored in drums.
– * Scum- a layer of dirt or froth on the surface of a liquid
– ** Volatile -easily evaporated at normal temperatures
• Washability
– It must be possible to remove excess penetrants from component surfaces
easily without affecting the penetrant within any defects.

14. • Drying characteristics
– A penetrant must resist drying out, and complete bleed out, during hot-air
drying of the component after the wash operation has been completed.
• Visibility
– a good, deep colour can be given to the penetrant by a comparatively
small amount of dye.
– If a large amount of dye is used in the formulation, the penetrating
abilities of the fluid could be reduced.
– Red is the most commonly used colour in dye penetrants as this
colour is the most readily seen by the human eye

15. Sensitivity Levels
• The higher the sensitivity level, the smaller the defect that
the penetrant system is capable of detecting
– Level 4 - Ultra-High Sensitivity
– Level 3 - High Sensitivity
– Level 2 - Medium Sensitivity
– Level 1 - Low Sensitivity

16. Developer
• Form
 Dry Powder
 Wet, Water Soluble
 Wet, Water Suspendable
 Wet, Non-Aqueous

17. Principles (6 Steps) of Liquid
Penetrant Inspection
1. Pre-Clean(Surface preparation)
2. Application of Penetrant
3. Removal of excess penetrant.
4. Development (Developer Application)
5. Observation and inspection.
6. Post-clean

18. Step 1-Pre-cleaning(surface
preparation)
• Parts must be free of dirt, rust, scale, oil, grease, etc.
to perform a reliable inspection.
• The cleaning process must remove contaminants
from the surfaces of the part and defects, and must
not plug any of the defects.

19. • Some machining, surface finishing and cleaning operations
can cause a thin layer of metal to smear on the surface and
prevent penetrant from entering any flaws that may be present.
• Etching of the surface prior to inspection is sometimes
required

20. Before Sanding
After Sanding
After Etching

21. Step 2- Application of Penetrant
• Many methods of application are possible such as:
– Brushing
– Spraying
– Dipping/
Immersing
– Flow-on
– And more

23. What is Dwell Time
• The penetrant solution must be
allowed to “dwell” on the surface of
the part to allow the penetrant time
to fill any defects present.
• The dwell time vary according to
penetrant type, temperature,
material type and surface finish.

24. Step 3- Removal of excess
penetrant
The removal technique depends upon the type
of penetrant used, as stated earlier…
– Solvent Removable
– Water Washable
– Post Emulsifiable

25. Solvent Removable
•The part is wiped with a clean dry cloth to remove the bulk of the excess
penetrant.
•Then, a cloth lightly dampened with solvent is used to remove any
remaining penetrant on the surface.
•Any time a solvent is used in the penetrant inspection process, a
suitable flash time is required to allow excess solvent to evaporate.
•They are supplied in aerosol cans for portability and are primarily used
for spot checks.

27. • It is often necessary, to inspect only a small area of a component, or to
inspect a component in situ rather than at a regular inspection station.
• There are two basic solvent types:
– flammable and non-flammable
• this system is extremely sensitive
• the costs are relatively high
• high material expense
• more labour-intensive process

28. Water Washable
• A coarse water spray is used to remove the excess penetrant.
• The procedure used as a guideline for the inspection will specify water
temperature (typically 50-100°F) and pressure (typically not more than
40 psi), etc.
• They are the easiest to employ and most cost effective when inspecting
large areas.

29. • Processing conditions
– water pressure and temperature
– duration of rinse cycle
– surface condition of the workpiece
– inherent removal characteristies of the penetrant

30. Post Emulsifiable
•When it is necessary to detect minute defects, high-sensitivity penetrants
that are not water washable, a post emulsifiable system is used.
•This involves an additional step in which an emulsifier is applied to the
surface of the part after the penetrant dwell time.
•The emulsifier is given just enough time to react with the penetrant on
the surface to render it water washable but not enough time to diffuse
into the penetrant trapped in the defects.
*Emulsifiable-- concentrate formulations are a
blend of active ingredient, organic solvent, and
surfactants. When the solution is diluted into
water, a spontaneous milky emulsion forms with
dispersed phase droplets in the size range of 1
to 25 μm.
*surfactants --a substance which tends to
reduce the surface tension of a liquid in which it
is dissolved

31. • An emulsifier is applied after the penetrant has had sufficient time to be
absorbed into defects.
• Small flaws that are often missed because of the penetrant being washed
out are more likely to be identified by the use of this system.
• Disadvantages
– more expensive
– emulsifier costs & additional time
– additional handling equipment and space

32. Step 4- Development (Developer
Application)
• In order to attain optimum inspection conditions, developers are
designed to work with specific penetrants
• The role of the developer is to pull trapped penetrant out of defects and
to spread it out on the surface so that it can be seen.
• Also provides a light background to increase contrast when visible
penetrant is used.
*Non-Aqueous -made from, with, or by means of a liquid other than water.

33. • Absorption.
• Application
• Background masking
• Physical characteristics
• Chemical characteristics

34. • Developer materials
– Dry Powder
– Wet, Water Suspendable
– Wet, Water Soluble
– Wet, Non-Aqueous

35. Dry Powder Developer
• Prior to applying a dry powder developer, the component
must be thoroughly dried. Drying is usually accomplished in
a hot air circulating oven.
• The developer is then applied by immersing the part in the
powder or by dusting of the part with the powder.
• The part can also be placed in a developer dust cloud
chamber

36. Wet Developer (water- suspended and water- soluble)
• Wet developers are applied by
immersing or spraying the part while it
is still wet from the penetrant removal
process.
• The part is completely coated and the
excess liquid allowed to drain to
prevent pooling
• The part is then dried in a hot air
circulating oven

37. Nonaqueous Developer
• Nonaqueous developer is applied by a aerosol spray to a thoroughly
dried and cooled part.
• A thin even coating should be applied.
• The coating should be white but still slightly transparent when
performing a visible dye penetrant inspection, and even thinner when
performing a fluorescent penetrant inspection.

38. Step 5- Observation and
inspection
• In this step the inspector evaluates the penetrant indications against
specified accept/reject criteria and attempts to determine the origin of
the indication.
• The indications are judged to be either relevant, non-relevant or false.
Non-relevant weld geometry indications
Relevant crack indications from an
abusive drilling process

39. Step 6- Post Clean
• The final step in the penetrant inspection process is to thoroughly clean
the part that has been tested to remove all penetrant processing
materials.
• The residual materials could possibly affect the performance of the part
or affect its visual appeal

40. Advantages of Penetrant Testing
• Relative ease of use.
• Can be used on a wide range of material types.
• Large areas or large volumes of parts/materials can be
inspected rapidly and at low cost.
• Parts with complex geometries are routinely inspected.
• Indications are produced directly on surface of the part
providing a visual image of the discontinuity.
• Initial equipment investment is low.
• Aerosol spray cans can make equipment very portable.

41. Limitations of Penetrant Testing
• Only detects surface breaking defects.
• Requires relatively smooth nonporous material.
• Precleaning is critical. Contaminants can mask
defects.
• Requires multiple operations under controlled
conditions.
• Chemical handling precautions necessary (toxicity,
fire, waste).
• Metal smearing from machining, grinding and other
operations inhibits detection. Materials may need to
be etched prior to inspection.
• Post cleaning is necessary to remove chemicals.

42. Applications of Penetrant Testing
• All defects that are open to the surface
– Rolled products-- cracks, seams, laminations
– Castings--cold shuts, hot tears, porosity, blow
holes, shrinkage
– Forgings– cracks, laps, external bursts
– Welds– cracks, porosity, undercut, overlap, lack
of fusion, lack of penetration

43. Rolled products-Seams

46. FORGING