LPI_Liquid Penetrant Inspection

MET312 NON-DESTRUCTIVE TESTING / MODULE#2 6/1/2022
Compiled By: SUKESH O P/ AP-ME/JECC 1
MET312 NON-DESTRUCTIVE
TESTING
MODULE-2 – LIQUID PENETRANT INSPECTION
Sukesh O P
Assitant Professor
Department of Mechanical Engineering,
Jyothi Engineering College, Cheruthuruthy
1
ME357 NON-DESTRUCTIVE TESTING
Introduction to NDT- Visual Inspection-
Liquid Penetrant Inspection- Magnetic
Particle Inspection- Ultrasonic Testing-
Radiography Testing- Eddy Current
Testing.
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MODULE-2
 Liquid Penetrant Inspection: principles,
properties required for a good penetrants and
developers - Types of penetrants and developers.
and advantages and limitations of various
methods of LPI - LPI technique/ test procedure-
interpretation and evaluation of penetrant test
indications, false indication and safety precaution
required in LPI, applications, advantages and
limitations.
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MODULE-2
 Liquid Penetrant Inspection: Principles – types and
properties of liquid penetrants – developers –
advantages and limitations of various methods -
Preparation of test materials – Application of
penetrants to parts, removal of excess penetrants, post
cleaning – Control and measurement of penetrant
process variables –selection of penetrant method –
solvent removable, water washable, post emulsifiable –
Units and lighting for penetrant testing – calibration-
Interpretation and evaluation of test results - dye
penetrant process applicable codes and standards.
SOP/ APME/JECC 4

LIQUID PENETRANT INSPECTION (LPI)
 Dye penetrant inspection (DPI), also
called liquid penetrant inspection (LPI)
or penetrant testing (PT), is a widely applied
and low-cost inspection method used to locate
surface-breaking defects in all non-porous
materials (metals, plastics, or ceramics).
 LPI is used to detect casting, forging and welding
surface defects such as hairline cracks, surface
porosity, leaks in new products, and fatigue
cracks on in-service components.
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PRINCIPLE
 DPI is based upon capillary action, where low surface
tension fluid penetrates into clean and dry surface-
breaking discontinuities. Penetrant may be applied to the
test component by dipping, spraying, or brushing.
 After adequate penetration time has been allowed, the
excess penetrant is removed and a developer is applied.
The developer helps to draw penetrant out of the flaw so
that an invisible indication becomes visible to the
inspector.
 Inspection is performed under ultraviolet or white light,
depending on the type of dye used - fluorescent or
nonfluorescent (visible).
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INSPECTION STEPS
1. Pre-cleaning
2. Application of penetrant
3. Removals of excess penetrant
4. Application of Developer
5. Inspection
6. Post cleaning
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PROCESSING STEPS OF LPI
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1. PRE-CLEANING
 The test surface is cleaned to remove any dirt, paint, oil,
grease or any loose scale that could either keep
penetrant out of a defect, or cause irrelevant or false
indications.
 Cleaning methods may include solvents, alkaline
cleaning steps, vapor degreasing, or media blasting. The
end goal of this step is a clean surface where any defects
present are open to the surface, dry, and free of
contamination.
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CLEANING METHODS
 Mechanical methods:
 Brushing
 Blasting
 Chemical methods:
 Hot solvent degreasing
 Vapor degreasing
 Cold solvent degreasing
 Alkaline degreasing
 Acid pickling
 Steam cleaning
 Paint strippers
Physical Cleaning
•Grinding
•Abrasive Blasting
•Wire brushing
Defect
Peened or Closed
Light Acid Etching
Light Acid applied
Thin layer of the
surface dissolved

Light Acid Etching
After Acid Etching
The defect opened again to the surface CHEMICAL METHODS
Hot Solvent Degreasing
Heating Element
Solvent
Components
Heating
Element
Solvent
Components
Condensor
Drip Tray
vapour
The most effective method for degreasing
Vapour Degreasing
STEAM CLEANING
 For large objects

2. APPLICATION OF PENETRANT
 After cleaning the surface from any type of foreign
contaminants, penetrants are applied may be by
immersing the job into penetrant dilution or by
brushing or by spraying.
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2. APPLICATION OF PENETRANT
 DWELL: It is a certain period of time for which
penetrant is left to be in contact with surface of
job till it dries. This dwell period varies according
to type of penetrant used, material on which
penetrant is applied, type of defect for which it is
applied, etc.
 Generally minimum dwell period varies up to 60
minutes.
 The specimens size, composition, temperature,
nature of discontinuity, all affect the penetration
time, which is also called as dwell time.
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3. REMOVALS OF EXCESS PENETRANT
 This is a very complicated step, where precise level
of care is required to remove the excess penetrant
from the surface while leaving penetrants for
defects also.
 It may be done by direct rinsing with water, by
cleaning with a solvent, or first treating it with
emulsifier, then rinsing with water.
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4. APPLICATION OF DEVELOPER
 For clear visualization of defect , a thin layer of developer
is applied on the surface of job, which draws out the
penetrant trapped in flaws back to the upper surface.
 Developer may be used in dry (dusting) or wet
form(dipping and brushing).
 Several developer types are available, including: non-
aqueous wet developer (NAWD), dry powder, water-
suspendable , and water-soluble. Choice of developer is
governed by penetrant compatibility and by inspection
conditions.
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5. INSPECTION
 Inspection of the test surface should take place
after 10-to-30 minute development time, depends of
product kind. This time delay allows the blotting
action to occur. The inspector may observe the
sample for indication formation when using visible
dye.
 The inspector will use visible light with adequate
intensity (100 foot-candles or 1100 lux is typical)
for visible dye penetrant. Ultraviolet (UV-A)
radiation of adequate intensity (1,000 micro-watts
per centimeter squared is common), along with
low ambient light levels (less than 2 foot-candles)
for fluorescent penetrant examinations.
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RESULTS -LPI
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6. POST CLEANING
 The test surface is often cleaned after inspection
and recording of defects, especially if post-
inspection coating processes are scheduled.
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CHARACTERISTICS/PROPERTIES REQUIRED
FOR A GOOD PENETRANTS
 Chemical stability & uniform physical
consistency
 High degree of wettability
 Quick & complete penetrability
 Low viscosity
 Sufficient brightness & permanence of
colour
 Chemical inertness
 Low toxicity
 Slow drying
 Ease of removal
 Low cost
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PENETRANT PROPERTIES
 Wetting ability
 Specific gravity
 Volatility
 Chemical activity
 Solubility
 Solvent ability
 Health hazard
 Tolerance to
contaminants
 Flammability / flash
point
 Electrical
conductivity
 Availability and
cost
 Wetting ability:
 Affect penetrability and bleed-back characteristics
 Contact angle and surface tension of penetrant
control wetting ability
 Specific gravity:
 Ratio of density of penetrant with density of distilled
water at 40C
 Not a problem with oil base penetrant
 Penetrant used in tank system must have specific
gravity less than 1
 to ensure water will not float on top of penetrant
 prevent penetrant from covering the test object
 Flash point:
 Temperature at which enough vapor is given
off to form combustible mixture
 Typical min 93C
 Should not be flammable
 Volatility:
 Characterize by vapor pressure or boiling point
 Good penetrant usually evaporate too quickly
 Low volatility is desirable  so the penetrant
dry from the surface, leave stained and from
any discontinuity, leave precipitated dye
 Chemically inert:
 Must be inert, non-corrosive as possible  chemically
compatible with the material being tested
 Penetrant is contaminant (contain sulphur, sodium,
halogen)  potential reactions must be considered
 To avoid possibility of embrittlement or cracking over
years
 Viscosity:
 Affect thickness of penetration due to molecular/internal
friction
 Low viscosity penetrant
 Solubility:
 Penetrant contain dye in liquid solution
 Must hold sufficient dye at ambient or high temperature
 Must not come out from solution if temperature drop

 Solvent ability:
 Solvent must be able to remove surplus
penetrant from test specimen
 To ensure clean, clear background
 Must not dissolve the penetrant in defect
 Tolerance to contaminants:
 Penetrant will be contaminated after a period
of time, even if a great care is taken
 Must be periodically check to ensure all is well,
no residue left
 Health hazard:
 Must comply with or exceed the most stringent HSE
requirements
 Toxicity, odour, skin contact
 To prevent allergies or contaminants
 Availability and cost:
 Dye materials are easily obtained
 Low cost
 Electrical conductivity:
 Electrostatic spraying becomes popular
uniform coverage with complicated shapes
Reduces over spraying
Requires less penetrant over all
 Spray gun applies –ve charge to penetrant
 Test object ground potential
 Electrostatic attraction cause penetrant be
strongly attracted to the part
 low viscosity and easily attracted to the part
Must readily accept and hold the electrical charge
DEVELOPER PROPERTIES
 Good developer:
 Material must be absorptive to perform blotting
action
 Must have fine texture
 Must mask out background contours and colors
 Must be easily and evenly applicable
 Must form light and even coat
 Must be no fluorescing of developer when
fluorescent penetrant is used
 Penetrant bleeding must easily wet the material
 Must be high color contrast, white is the best
 Must be readily removable after test
 Must be in-toxic and non-irritant

TYPE OF PENETRANTS
 For different materials inspection penetrant
manufactures have developed different penetrant
for proper inspection.
 For small defect and smooth surface penetrants
required are some different kind. Similarly for
large defects.
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TYPE OF
PENETRANTS/DEVELOPERS
Penetrant Type
I Fluorescent
II Visible
Method
A Water Washable
B Postemulsifiable - Lipophilic
C Solvent Removable
D Postemulsifiable - Hydrophilic
Developer Form
Dry Powder
Wet, Water Soluble
Wet, Water Suspendable
Wet, Non-Aqueous
TYPE OF PENETRANTS
 in which a fluorescent dye is applied to the
surface of a non-porous material in order to
detect defects that may compromise the integrity
or quality of the part in question. Noted for its
low cost and simple process, FPI is used widely in
a variety of industries.
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APME/JECC FLUORESCENT PENETRANTS
V/S VISIBLE PENETRANTS
Fluorescent penetrants Visible penetrants
It consist of dyes that flouresce, when
ultraviolet radiations are exposed on
them.
It consists of red dye, which produces
a fine range of contrast against the
white developer background.
They are more sensitive. They are less sensitive.
It requires darkened area and
ultraviolet radiations for inspection.
It doesn't require any dark area and
ultraviolet radiations for inspection.
They are more vulnerable to
contamination
They are less vulnerable to
contamination
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WHY IS VISIBLE PENETRANT RED AND
FLUORESCENT PENETRANT GREEN?
•Visible penetrant is
usually red because red
stands out and
provides a high level of
contrast against a light
background
•Fluorescent penetrant
is green because the
eye is most sensitive to
the color green due to
the number and
arrangement of the
cones (the color
receptors) in the eye.
PENETRANT METHODS
 Method A- Water washable
 Method B- Post-emulsifiable, Lipophilic(oil base)
 Method C- Solvent removable
 Method D- post-emulsifiable, Hydrophilic(water
base)
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PENETRANT METHODS
METHOD A- WATER WASHABLE
 Water washable penetrants are also referred to
as self-emulsifying penetrants. This penetrants
consists of an emulsifying agent namely
detergents, which helps it get removed from the
part by rinsing with water only.
 ADV:-
 Sensitivity is high
 Cost involved is less
 Large surface discontinuities can be visualized
 Removal of penetrant is very easy
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PENETRANT METHODS
METHOD A- WATER WASHABLE
DIS ADV:-
 Dark environment is required for evaluation
 Insensitive to shallow discontinuities
 Method is not portable
 Quality of penetrant is degraded by contamination.
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PENETRANT METHODS
METHOD B&D- POST-EMULSIFIABLE , LIPOPHILIC &
HYDROPHILIC
 Post emulsifiable penetrants come in two
categories:
Lipophilic and hydrophilic.
Where lipophilic are oil soluble, it interacts with oil-
based emulsifier to make removal possible and
hydrophilic are water soluble. It interacts with
detergent based emulsifier to remove the excess
penetrant with water wash only.
ADV:-
 Sensitivity is high for small discontinuities
 Sensitive to shallow discontinuities
 Not affected by acids.
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PENETRANT METHODS
METHOD B&D- POST-EMULSIFIABLE , LIPOPHILIC &
HYDROPHILIC
Limitation :-
 Method is not portable
 It requires an emulsifier
 Takes more time
 In effective for complex and rough surfaces.
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PENETRANT METHODS
METHOD C SOLVENT REMOVABLE
Solvent removable penetrants uses solvents for
penetrant removal from surface.
ADV:-
 Sensitive to discontinuities of spot size.
 When water removal fails, it provides feasible technique.
LIMITATION:-
 Limited to small areas
 Black light and dark environment is required.
 Back ground indications are also generated, which affects
the contrast ratio
 Sensitivity reduces if excess remover is used.
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DEVELOPER TYPES
The primary methods for the following main
developer types :
– Dry
– Wet (water- suspended and water- soluble)
– Nonaqueous Wet

DEVELOPER TYPES
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.
DEVELOPER TYPES
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.
DEVELOPER TYPES
NONAQUEOUS DEVELOPER (SOLVENT-
SUSPENDED)
•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.
INTERPRETATION AND EVALUATION
OF PENETRANT TEST INDICATIONS
 LPI indications depend on the type of penetrant
used.
 If fluorescent penetrant is used, defect show-up
as glowing yellow-green dots or lines against a
dark background.
 In the case of die penetrant ; defects are
indicated as red dots or lines against a white
background.
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INTERPRETATION AND EVALUATION OF
PENETRANT TEST INDICATIONS
 The interpretation of the characteristic patterns
indicating the types of flaws is of great significance.
For example, a crack of a small opening is indicated
by a line of penetrant.dots of penetrant indicate pits or
porosities on the surface of object under inspection.
Such dots appear over an area or isolated spots and
generally do not from a line pattern. A series of dots
forming a line pattern indicates a tight track, cold
shut or partially welded lap. Fatigue cracks also
generally appear in the form of a series of very fine
dots.
 May obtain a rough estimate of the surface opening
by measuring the width of the indication( the amount
of spreading of the penetrant on the developer). There
doesn’t exist a definite relationship between the
surface opening and spreading of the penetrant.
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SAFETY PRECAUTIONS
 Proper cleaning is necessary to assure that
surface contaminants have been removed and
any defects present are clean and dry. Some
cleaning methods have been shown to be
decrimental to test sensitivity, so acid etching to
remove metal smearing and re-open the defect
may be necessary. Penetrant dyes stain cloth,
skin and other porous surfaces brought into
contact.
 One should verify compatibility on the test
material, especially when considering the testing
of plastic components.
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SAFETY PRECAUTIONS
HEALTH AND SAFETY PRECAUTIONS
 Chemical Safety : Before working with a
chemical of any kind, it is highly recommended
that the material safety data sheets (MSDS) be
reviewed so that proper chemical safety and
hygiene practices can be followed.
 Some of the penetrant materials are flammable
and, therefore, should be used and stored in
small quantities. They should only be used in a
well ventilated area and ignition sources avoided.
 Eye protection should always be worn to prevent
contact of the chemicals with the eyes. Gloves
and other protective clothing should be worn to
limit contact with the chemicals.
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SAFETY PRECAUTIONS
HEALTH AND SAFETY PRECAUTIONS
 Ultraviolet Light Safety: Ultraviolet (UV) light
has wavelengths ranging from 180 to 400
nanometers. These wavelengths place UV light in the
invisible part of the electromagnetic spectrum
between visible light and X-rays.
 Skin and eye damage occurs at wavelengths around
320 nm and shorter which is well below the 365 nm
wavelength, where penetrants are designed to
fluoresce. Therefore, UV lamps sold for use in
penetrant testing are almost always filtered to
remove the harmful UV wavelengths. The lamps
produce radiation at the harmful wavelengths so it is
essential that they be used with the proper filter in
place and in good condition.
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APPLICATIONS
 Turbine rotor discs & blades
 Aircraft wheels, castings, forged components,
welded assemblies
 Automotive parts – pistons, cylinders, etc.
 Bogie frames of railway locomotives & rolling
stock
 Electrical ceramic parts – spark plug insulators,
glass-to-metal seals, etc.
 Moulded plastic parts
ADVANTAGES & LIMITATIONS OF
LIQUID PENETRANT METHOD
ADVANTAGES
 Simple & inexpensive
 Versatile & portable
 Applicable to ferrous,
non-ferrous, non-
magnetic & complex
shaped materials
which are non-porous
& of any dimension
 Detects cracks, seams,
lack of bonding, etc.
LIMITATIONS
 Detect surface flaws
 Non-porous surface
for material
 Surface cleaning
before & after
inspection
 Deformed surfaces &
surface coatings
prevent detection
In general, penetrant testing is more effective at
finding:
 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.
 Flaws with rough fracture surfaces than smooth
fracture surfaces.
 Flaws under tensile or no loading than flaws
under compression loading.
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MODULE-2(SUMMARY)
•Penetrant testing (PT) is one of the most
widely used nondestructive testing
methods.
•Its popularity can be attributed to two
main factors, which are its relative ease of
use and its flexibility.
•However, PT involves a number of
processing steps that must be closely
control to achieve optimal sensitivity.

GLOSSARY OF TERMS
•Capillary Action - the tendency of certain
liquids to travel or climb when exposed to
small openings.
•Contrast - the relative amount of light
emitted or reflected between and indication
and its background.
•Defect - a discontinuity that effects the
usefulness of a part or specimen.
•Developer - a finely divided material
applied over the surface of a part to help
promote reverse capillary action and thus
bring out a penetrant indication.
GLOSSARY OF TERMS
•Discontinuity - any interruption in the
normal physical structure of a part or weld. It
may or may not affect the usefulness of a part.
•Dwell Time - the period of time that a
penetrant or developer must remain in contact
with the surface of a part under test.
•Emulsification Time - the time allowed for
the emulsifier to render the penetrant water
washable and thus allow the part to be washed.
•Emulsifier - a material applied over a film of
penetrant that renders it water washable.
GLOSSARY OF TERMS
•Evaluation - the process of deciding as to the
severity of the condition after an indication has
been interpreted.
•False Indication - an indication caused by
improper processing; not caused by a relevant
or non-relevant condition.
•Flash Time - the time required for the solvent
to evaporate from the surface of a part when
used to preclean or remove excess penetrant.
•Fluorescent Dye - a dye which becomes
fluorescent (gives off light) when exposed to
short wave radiation such as ultraviolet light.
GLOSSARY OF TERMS
•Indication - the visible evidence or
penetrant bleed-out on the surface of the
specimen
•Interpretation - the process of evaluating
an indication in an attempt to determine
the cause and nature of the discontinuity.
•Non-Aqueous Developer - a developer in
which developing powder is applied as a
suspension in a quick drying solvent
•Penetrant - a liquid used in fluorescent or
visible dye penetrant inspection to
penetrate into the surface openings of parts
inspected via these methods

GLOSSARY OF TERMS
•Relevant Indication - an indication that has
been determined not to be false or non-relevant -
and actual discontinuity
•Seeability - the characteristic of an indication
that enables it to be seen against the adverse
conditions of background, outside light, etc.
•Sensitivity - the ability of a penetrant to detect
surface openings. Higher sensitivity indicates
smaller discontinuities can be detected
•Ultraviolet Light (or Black Light) - light energy
just below the visible range of violet light (356
nanometers).
GLOSSARY OF TERMS
•Viscosity - the resistance of a fluid to the
motion of its particles
•Washability - the property of a penetrant
which permits it to be cleaned from the
surface of a part by washing with water
MET312 NDT
ASSIGNMENT 1 (MODULE-1&2)
1. Explain about computer enhanced system used for
visual Inspection.
2. Explain the special lighting system and various light
sources used for Visual inspection.
3. Explain about Control and measurement of penetrant
process variables in LPI
4. Write Shortnotes on dye penetrant process applicable
codes and standards.
Submit on or before: 14-06-2022,11AM
(in class note- submit in the Hardcopy n upload
in google classroom)
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MET312 NDT
END OF MODULE -2
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OPEN TEST -2
1. Write short notes on liquid penetrant inspection.
Discuss the principle of Liquid Penetrant Inspection.
2. Give short notes on Penetrants. Name the basis on
which penetrant is classified.
3. Write short notes on Visual Perception. Name the
optical aids used in visual inspection
4. Explain the fluorescent and visible penetrant. State
the characteristics of good penetrants.
5. Explain the different penetrant properties.
6. Discuss the safety precautions needed to conduct LPI
7. Explain in detail about different penetrant methods.
8. Explain the different factors effecting visual
inspection.
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LPI_Liquid Penetrant Inspection

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