Liquid Penetrant Inspection (LPI)- NDT

ME367 NON-DESTRUCTIVE TESTING
MODULE-2
Sukesh O P, AP-ME , JECC10/16/2018
SUKESH O P/ APME/JECC 1

ME357 Non-Destructive Testing
10/16/2018SUKESH O P/ APME/JECC
2
Introduction to NDT- Visual Inspection- Liquid
Penetrant Inspection- Magnetic Particle
Inspection- Ultrasonic Testing- Radiography
Testing- Eddy Current Testing.

MODULE-2
3
 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.

Liquid Penetrant Inspection (LPI)
4
 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.

Principle
5
 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 - flurescent or
nonfluorescent (visible).

Inspection steps
6
1. Pre-cleaning
2. Application of penetrant
3. Removals of excess penetrant
4. Application of Developer
5. Inspection
6. Post cleaning

Processing steps of LPI
7

1. Pre-cleaning
8
 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.

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

16
 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.

17
 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.

3. Removals of excess penetrant
18
 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.

4. Application of Developer
19
 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.

5. Inspection
20
 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.

RESULTS -LPI
21

6. Post Cleaning
22
 The test surface is often cleaned after inspection
and recording of defects, especially if post-
inspection coating processes are scheduled.

Characteristics/Properties required for a good
penetrants
23
 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

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
32
 For different materials inspection penetrant
manufactures have developed different penetrant
for proper inspection.
 For small defect and smooth surface penetrants
required are some dirrerent kind. Similarly for
large defects.

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
34
 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.

Fluorescent penetrants
V/s Visible penetrants
35
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

Penetrant methods
37
 Method A- Water washable
 Method B- Post-emulsifiable, Lipophilic(oil base)
 Method C- Solvent removable
 Method D- post-emulsifiable, Hydrophilic(water
base)

Penetrant methods
Method A- Water washable
38
 Water washable penetrants are slso 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

Penetrant methods
Method A- Water washable
39
DIS ADV:-
 Dark environment is required for evaluation
 Insensitive to shallow discontinuities
 Method is not portable
 Quality of penetrant is degraded by contamination.

Penetrant methods
Method B&D- Post-emulsifiable , Lipophilic & Hydrophilic
40
 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.

Penetrant methods
Method B&D- Post-emulsifiable , Lipophilic & Hydrophilic
41
Limitation :-
 Method is not portable
 It requires an emulsifier
 Takes more time
 In effective for complex and rough surfaces.

Penetrant methods
Method C Solvent removable
42
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.

Developer types
The primary methods for the following main
developer types will be covered in the following
slides.
– 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
47
 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.

INTERPRETATION AND EVALUATION
OF PENETRANT TEST INDICATIONS
48
 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.

SAFETY PRECAUTIONS
49
 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 detrimental 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.

SAFETY PRECAUTIONS
Health and Safety Precautions
50
 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.

SAFETY PRECAUTIONS
Health and Safety Precautions
51
 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.

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

54
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.

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

ME367 NDT
TASK -2 (MODULE-2)
62
 Explain Quality and process control of LPI.
 Explain about the various test stations of LPI.
Submit on or before : 29/8/17 (in class note)

ME367 NDT
63
END OF MODULE -2

10/16/2018
64
SUKESH O P/ APME/JECC

Liquid Penetrant Inspection (LPI)- NDT

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