Dye penetrant testing (LPI) is a widely used method for detecting surface discontinuities by applying a liquid dye that seeps into flaws, followed by a developer that extracts the dye for visibility. The process involves several stages, including pre-cleaning, penetrant application, dwell time, removal of excess dye, applying a developer, and interpretation of results, which can be performed under normal or UV light. While effective for surface defects, this method has limitations in detecting subsurface flaws and is heavily dependent on thorough pre-cleaning.

1. DYE PENETRANT
TESTING
Presented by : Kalilahamed.J ,
Date : 10.07.2020

2. Introduction
• Penetrant examination is generally considered to be one of the easiest methods to locate discontinuities that
are open to the surface
• Penetrant testing is also commonly called as Liquid penetrant inspection (LPI), Liquid
• Penetrant testing, (LPT), Dye Testing (DT) or Dye Penetrant testing (DPT).
Principle
• A liquid Penetrant or dye is applied on the test surface and it is allowed to seep through the openings at the
surface such as a crack or surface pore.
• After sufficient time is given for the dye to seep through even minute opening, the dye on the surface is
removed.
• The dye that has seeped through the openings comes out and is seen. To assist in the drawing out of the dye
form the opening a developed is applied which acts as a blotting agent for drawing the dye out and acting as
a contrast for seeing the colored dye.

3. Stages of Penetrant Testing
1) Pre-cleaning
2) Application of the penetrant.
3) Allow time for penetration-Dwell time
4) Removal of excess penetrant from the surface
5) Application of developer.
6) Allow for developing of indication - Developing time
7) Interpretation and Evaluation.
8) Final cleaning.

4. Normal Light
OR
Dark (UV) Light

5. Requirements:
1. Cleaner - Basically acetone and other solvents
2. Penetrant
3. Developer
4. UV (Black) light source (If applicable)
Wave length of UV light = 10 – 380 nm
Wave length of dark light = 320 – 380 nm
• Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular
interactions when the two are brought together. The degree of wetting is known as Wettability or Body.
• Wetting is important and responsible for the effect Capillary action.
• Capillary action, or capillarity, is the ability of a liquid to flow in narrow spaces without the assistance of, and in
opposition to external forces like gravity.

6. STEPS
1. Pre-Cleaning:
• Is done to make the surface opening flaws to act like excellent capillars.
• The surface must be free of oil, grease, water, or other contaminants that may prevent penetrant from entering
flaws.
• Chemical mode of cleaning is more preferred than mechanical mode.
2. Application of Penetrant
• The Penetrant is a red or pink colored liquid and is available in spray cans or bottles. The Penetrant can be sprayed
from aerosol cans, brushed using a paint brush, swabbing, pouring or dipping. The method of application depends
upon the size of the component and the type of component.
• The dye is applied uniformly to the surface of the part and allowed time to seep into surface breaking defects by
capillary action.
Component
Dye

7. Penetrant (Dye):
A penetrant must possess some important characteristics as follows
• Spread easily over the surface of the material being inspected to provide complete and even coverage.
• Be drawn into surface breaking defects by capillary action.
• Remain in the defect but remove easily from the surface of the part.
• Remain fluid so it can be drawn back to the surface of the part through the drying and developing steps.
• Be highly visible or fluoresce brightly to produce easy to see indications.
• Not be harmful to the material being tested or the inspector.
• Penetrant materials come in two basic types.
Type 1 - Fluorescent Penetrants
Type 2 - Visible Penetrants

8. 3) Dwell Time.
• Dwell time is the total time that the dye is in contact with the surface.
• The dwell time is important because it allows the penetrant the time necessary to seep or be drawn into a defect
• It is decided by
The surface tension of the penetrant.
The contact angle of the penetrant.
The dynamic shear viscosity of the penetrant
The atmospheric pressure at the flaw opening.
The capillary pressure at the flaw opening.
The pressure of the gas trapped in the flaw by the penetrant.
The radius of the flaw or the distance between the flaw walls.
The density or specific gravity of the penetrant.
• Usual dwell time is = 5 – 60 mins
• The temperature of the specimen is an important factor . Usually at 10 to 45 deg C ,the usual liquid penetrants work
normally well.

9. 4) Removal of Excess Penetrant:
• Excess Dye = Dye that present on the flaw free regions of the surface.
• After sufficient dwell time, the excess penetrant on the specimen surface is
to be removed. This has to be done without disturbing the penetrant, which has
entered into the discontinuity.
• Complete removal of surface penetrant is effected to ensure against formation
of irrelevant indications.
• The excess penetrant is first removed by a clean lint -free dry cloth.
• The cloth is then moistened with the solvent recommended by the penetrant manufacturer and the penetrant is
gently wiped off from specimen surface. In any case, the solvent should not be flooded on the specimen surface or
otherwise it might wash out or dilute the penetrant in the discontinuity.
• Depending on the dye system used, the excess dye may be removed by
(i) Cleaning with solvents
(ii) Direct rinsing with water
(iii) First treating the part with an emulsifier and then rinsing with water.
Component
Excess
Dye
Required
Dye

10. • Penetrants classified by the method used to remove the excess penetrant from the part.
Method A - Water Washable
Method B - Post-Emulsifiable, Lipophilic
Method C - Solvent Removable
Method D - Post-Emulsifiable, Hydrophilic
• Method A - Water Washable
• Water washable penetrants can be removed from the part by rinsing with water alone
• These penetrants contain an inbuilt emulsifying agent (detergent)
• It makes possible to wash the penetrant from the part surface with water alone
• Water washable penetrants are sometimes referred to as self-emulsifying systems
• Easy and complete removal of excess dye is possible in a cheap manner
• However, there is a possibility of removing the dye from the flaws also, leading to missing of minute data
EASY WASHING BUT POOR SENSITIVITY

11. Method B – Post Emulsifiable (Lipophilic)
• Lipophilic systems make use of oil-based emulsifiers that interacts with the excess penetrant and remove them.
• They work with both a chemical and mechanical action.
• After the emulsifier has coated the surface of the object, mechanical action starts to remove some of the excess
penetrant as the mixture drains from the part.
• During the emulsification time, the emulsifier diffuses into the remaining penetrant and the resulting mixture is easily
removed with a water spray.
Method C - Solvent Washable
Solvent removable penetrants require the use of a solvent to
remove the penetrant from the part. The same cleaner is used as
penetrant remover
• Difficult and incomplete removal of excess dye is possible
• Incomplete removal of excess dye may lead to wrong indications which may confuse the inspector
TOUGH WASHING BUT GOOD SENSITIVITY

12. Method C : Solvent Washable:
• Solvent removable penetrants require the use of a solvent to remove the penetrant from the part.
• The same cleaner is used as penetrant remover
• Difficult and incomplete removal of excess dye is possible
• Incomplete removal of excess dye may lead to wrong indications which may confuse the inspector
TOUGH WASHING BUT GOOD SENSITIVITY
Post Emulsification:
• It is having the advantages of both water washable and solvent washable systems
• There is no over washing as well as under washing
• Better sensitivity and easy washing
• A separate emulsifier is added externally over the excess dye and the emulsifier converts the solvent washable excess
dye into water washable excess dye
Emulsifier
Dye

13. Method D : Post Emulsifiable (Hydrophilic)
• They use an emulsifier that is a water soluble detergent which lifts the excess penetrant from the surface of the part
with a water wash.
• They also remove the excess penetrant with mechanical and chemical action
• But the action is different because no diffusion takes place.
• They are basically detergents that contain solvents and surfactants.
• They break up the penetrant into small quantities and prevents these pieces from recombining or reattaching to the
surface of the part.
• The mechanical action of the rinse water removes the displaced penetrant from the part and causes fresh remover to
contact and lift newly exposed penetrant
from the surface.

14. 5. Developing:
• A developer (chalk powder) is applied to pull the trapped penetrant out the defect and spread it on the surface
• They are applied by dusting (dry powdered), dipping, or spraying (wet developers).
• The purpose of developer application is two-fold; on one hand by reverse capillary action, it draws out penetrant from
the discontinuities and spread it out on a greater area. On the other hand, it also serves as a colour contrast background
for dye-material.
• Parts should be allowed to develop for a minimum of 5 minutes and no more than 2 hours before inspecting.
Red indication on a white background. Incase of fluorescent dyes, Dark light is used to view the indications
DEVELOPER
PART
INDICATION

15. DEVELOPER
• The role of the developer is to pull the trapped penetrant material out of defects and spread it out on the surface of the
part so it can be seen by an inspector.Simply chalk powder either in dry from or dissolved in a volatile solvent
Form A - Dry Powder
Form B - Water Soluble
Form C - Water Suspendable
Form D - Nonaqueous Type 1 Fluorescent (Solvent Based)
Form E - Nonaqueous Type 2 Visible Dye (Solvent Based)
Form F - Special Applications
• Developer
1) Highly absorptive
2) Fine grain size & particle shape for easy dispersion
3) Provision of contrast background
4) Easy application
5) Formation of thin uniform coating over surface
6) Easily wettable
7) Low toxicity

16. 5. Interpretation
Visual inspection is the final step in the process.
Visible Penetrants = Normal light
Fluorescent Penetrants = UV light
As soon as flaws bleed out, the indications may run to larger spots, depending on size and depth, and it is difficult to
derive quantitative information on the flaw from the indication.
Approximate data about the type, size and depth of defect obtained
Applicability w.r.t Flaws.
• LPT is best for detecting
• Small round defects than small linear defects
• Deeper flaws than shallow flaws
• Flaws with a narrow opening at the surface than wide open flaws
• Flaws on smooth surfaces than on rough surfaces

17. Advantage:
1) Can detect surface defects
2) Can inspect parts with irregular shapes easily.
3) Fast method of inspection and indications are visible directly on the specimen surface.
4) Considered low cost compared to many other NDT methods.
5) Is a very portable inspection method.
Disadvantage:
1) Can not detect subsurface and internal flaws
2) Can not be used on extremely porous materials.
3) Precleaning of components is a critical step for better flaw detectability.
4) Results are qualitative

18. THANKYOU