ASNT Level II
Study Guide
Liquid Penetrant
Testing Method
Published by
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IBN-13: 978-1-57117-092-7
ISBN-10: 1-57117-092-8
Published by the American Society for Nondestructive Testing, Inc.
PRINTED IN THE UNITED STATES OF AMERICA.
first printing 1998
second printing with revisions 10/02
third printing 08/07
Contents
Contents.....................................................................................................................................................iii
Introduction.............................................................................................................................................vii
Chapter 1, Overview of Liquid Penetrant Testing....................................................................................1
History of Liquid Penetrant Testing .....................................................................................................1
Principles of Liquid Penetrant Testing ...................................................................................................1
Advantages of the Penetrant Process ...............................................................................................I
Disadvantages of the Penetrant Process...............................................................................................1
Basics of the Penetrant Process ..............................................................................................................2
Preparation of Parts for Penetrant Testing ........................................................................................2
Surface Condition .......................................................................................................................2
Penetrant System.................................................................................................................................3
System Sensitivity ........................................................................................................................3
Type of Penetrant............................................................................................................................3
Advantages of Fluorescent Liquid Penetrants ...........................................................................4
Advantages of Visible Dye Penetrants .....................................................................................4
Selection of Liquid Penetrant Material and Process .....................................................................5
Fluorescent Liquid Penetrant ...................................................................................................5
Visible Dye Liquid Penetrant ...................................................................................................5
Penetrant Application...........................................................................................................................5
Penetrant Dwell ............................................................................................................................5
Temperature ..................................................................................................................................6
Penetrant Removal Method .............................................................................................................6
Water Washable (Method A) .......................................................................................................6
Lipophilic Emulsifier (Method B) ...............................................................................................7
Solvent Removable (Method C) .................................................................................................8
Hydrophilic Emulsifier (Method D) ...........................................................................................8
Drying ................................................................................................................................................ .8
Develop the Indication ......................................................................................................................8
Inspection............................................................................................................................................8
Importance of the Inspector's Evaluation .....................................................................................9
Penetrant Inspection Documents .................................................................................................9
Visual Requirements.......................................................................................................................9
Classification of Discontinuities by Origin ..................................................................................9
Identifying Indications ...............................................................................................................10
Postcleaning ....................................................................................................................................11
Chapter 2, Penetrants, Developer and Equipment ..............................................................................13
Penetrants ............................................................................................................................................13
Characteristics of Penetrants ...........................................................................................................13
Surface Tension ..........................................................................................................................13
Wetting Ability..............................................................................................................................13
Capillary Action ..........................................................................................................................13
Physical Properties of Penetrants ...................................................................................................14
Viscosity ....................................................................................................................................14
Volatility ....................................................................................................................................14
Specific Gravity .........................................................................................................................14
Flash Point ..................................................................................................................................14
Thermal Stability ........................................................................................................................14
Chemical Properties of Penetrants................................................................................................... .14
Inertness ....................................................................................................................................14
Removability ..............................................................................................................................15
Water Tolerance............................................................................................................................15
Developer ............................................................................................................................................15
Dry Powder ....................................................................................................................................16
Water Soluble ..................................................................................................................................16
Water Suspended ............................................................................................................................16
Nonaqueous ....................................................................................................................................17
Specific Application .......................................................................................................................17
Material and Process Control Tests .....................................................................................................17
Ultraviolet Light Intensity .............................................................................................................19
Emulsifier Concentration...................................................................................................................19
Ambient White Light Intensity..........................................................................................................19
Penetrant Inspection Area Cleanliness ...........................................................................................19
Penetrant Materials Testing...............................................................................................................19
Water Content...............................................................................................................................19
Separation of Constituents and Loss of Fluorescence ................................................................19
Washability ...............................................................................................................................19
Sensitivity Comparison .............................................................................................................19
Penetrant System Monitor......................................................................................................................19
Equipment ..........................................................................................................................................20
Ultraviolet Lighting .......................................................................................................................20
Stationary Processing Equipment ...................................................................................................21
Portable Processing Equipment.........................................................................................................21
Automated Equipment ....................................................................................................................22
Chapter 3, Testing in Primary Metals Production.................................................................................23
Producing Metals and Alloys .............................................................................................................23
Processing Discontinuities ..................................................................................................................23
Discontinuities Related to Metal Solidification.................................................................................23
Discontinuities in Metal Ingots ........................................................................................................23
Discontinuities in Metal Castings ...................................................................................................23
Discontinuities in Blooms and Billets .............................................................................................23
Discontinuities in Hot Rolled Bars, Shapes, Plate or Strip .............................................................24
Discontinuities in Forgings .............................................................................................................24
Discontinuities in Rolled and Pierced Products ..............................................................................24
Discontinuities in Extrusions .........................................................................................................24
Discontinuities in Cold Worked Metal Products .............................................................................24
Discontinuities in Fusion Welds .....................................................................................................25
Discontinuities in Heat Treating Processes .....................................................................................25
Discontinuities in Machined and Ground Surfaces .........................................................................25
Cracks During Plating or Chemical Treatment ..............................................................................25
Service Discontinuities..........................................................................................................................25
Fatigue Cracks ................................................................................................................................25
Significance of Surface Discontinuities under Repeated Loading or Vibration ........................25
Prevention of Fatigue Failure on Service ...................................................................................25
Stress Corrosion Cracking
................ ..............................................................................26
Other Causes of Service Damage.......................
..................................................................26
Continuous Line Indication..........................
..................................................................27
Intermittent Line Indications ...................
.............................................................................27
Rounded Areas of Indications ...........
.................................................................................27
Small Dot Indications........................................................................................................................27
Diffuse Indications ........................ . . . .......................................................................................27
Edges of Indications .......................... ........................................................................................27
Chapter 4, Appearance of Liquid Pentrant Indications . . . . . ............................................................27
Brilliance and Extent of Indications
.....................................................................................28
Persistence of Indications......................................................................................................................28
Other Variables Affecting Indication Appearance................................................................……...:... .28
Surface Conditions............................................................................................................................28
Temperature ...................................................................................................................................28
Dwell Time and Washing ...............
.....................................................................................28
Developer..........................................................................................................................................29
Previous Testing..............................................................................
.......................................29
Common Causes of Nonrelevant and False Indications ......................................................................29
Poor Process Control.........................................................................................................................29
Part Geometry and Surface Condition...............................................................................................30
Evaluation of Nonrelevant Indications...............................................
.....................................30
Review Questions.....................................................................................................................................31
Answers.....................................................................................................................................................37
Appendix, Standard Terminology for the Liquid Penetrant Examination..........................................39
VI
Introduction
Overview of the Study Guide
Resource Materials
This study guide contains basic information intended
to prepare a candidate for Level II penetrant inspection
examinations. This study guide does not present all of
the knowledge necessary for certification; the candidate
is expected to supplement this guide with the
recommended references that follow.
"Recommended reading" boxes, which list additional
areas of study and which Recommended References
contain the information, appear throughout the text.
ASM Handbook, 9th edition, Volume 17,
Nondestructive Evaluation and Quality
Control, Materials Park, OH, ASM
International, 1989.
Acknowledgments
The authors acknowledge the support of the
AlliedSignal Aerospace NDT Network and the
ASNT Technical Services Department staff for
assisting with the first edition of this book.
This revision was possible thanks to the contributions
of Bill Chedister, William Cook, Vilma Holmgren, Bill
Mooz and Thorn Schafer.
Recommended References
A. Tracy, Noel A., technical editor, Patrick O.
Moore, editor, Nondestructive Testing
Handbook, third edition: Volume 2, Liquid
Penetrant Testing, Columbus, OH, American
Society for Nondestructive Testing, Inc., 1999.
Recommended Practice No. SNT-TC-1A, 2001,
Columbus, OH, American Society for
Nondestructive Testing, Inc., 2001.
ANSI/ASNT CP-189-2001: ASNT Standard for
Qualification and Certification of Nondestructive
Testing Personnel, Columbus, OH, American
Society for Nondestructive Testing, Inc., 2001.
ASTM International, ASTM E 165, Standard Test
Method for Liquid Penetrant Examination, West
Conshohocken, PA, ASTM, 2001.
ASTM International, ASTM E 1208, Standard Test
Method for Fluorescent Liquid Penetrant
Examination Using the Lipophilic PostEmulsification Process, West Conshohocken, PA,
ASTM, 2001.
ASTM International, ASTM E 1209, Standard Test
Method for Fluorescent Liquid Penetrant
Examination Using the Water-Washable Process,
West Conshohocken, PA, ASTM, 2001.
B. Boisvert, Bernie, Principles and Applications
of Liquid Penetrant Testing: A Classroom
Training Text, Columbus, OH, American
Society for Nondestructive Testing, Inc., 1993.
ASTM International, ASTM E 1210, Standard Test
Method for Fluorescent Liquid Penetrant
Examination Using the Hydrophilic PostEmulsification Process, West Conshohocken, PA,
ASTM, 2001.
C. General Dynamics, Liquid Penetrant Testing
Programmed Instruction Handbook, PI-4-2,
Columbus, OH, American Society for
Nondestructive Testing, Inc., 1977.
ASTM International, ASTM E 1219, Standard Test
Method for Fluorescent Liquid Penetrant
Examination Using the Solvent-Removable
Process, West Conshohocken, PA, ASTM, 2001.
viii
ASTM International, ASTM E 1219, Standard Test
Method for Fluorescent Liquid Penetrant
Examination Using the Solvent-Removable
Process, West Conshohocken, PA, ASTM,
2001.
ASTM Internationa], ASTM E 1220, Standard
Test Method for Visible Penetrant
Examination Using Solvent-Removable
Process, West Conshohocken, PA, ASTM,
2001.
ASTM Internationa], ASTM E 1417, Standard
Practice for Liquid Penetrant Examination,
West Conshohocken, PA, ASTM, 2001.
ASTM International, ASTM E 1418, Standard Test
Method for Visible Penetrant Examination
Using the Water-Washable Process, West
Conshohocken, PA, ASTM, 2001.
SAE International, SAE AMS 2644, Inspection
Materials, Penetrant, Warrendale, PA, SAE
(Society of Automotive Engineers)
International, 2002.
Chapter 1
Overview of Liquid Penetrant Testing
History of Liquid Penetrant
Testing
Liquid penetrant testing is one of the oldest
methods of nondestructive testing. Its origin is
generally attributed to the inspection of wheel
axles in the railroad industry in the 1890s. It was
noticed that after oil was wiped off of a part
surface, the oil would reappear where a crack or
other type of discontinuity was located. This
discovery led to the oil-and-whiting test. Parts
were immersed in oil and then wiped with rags
dampened with kerosene. Powdered chalk was
used to dust the surface to increase the visibility of
any oil leaking back onto the part surface. Today's
liquid penetrant testing evolved from the oil-andwhiting test through continual improvements to the
type of oil used, the addition of dyes and the
creation of special removers and developers.
Principles of Liquid Penetrant
Testing
Liquid penetrant testing is based on the ability
of a liquid to seep into cavities that are open to the
surface and remain in the cavity when the excess
liquid is removed. The liquid remaining in the
cavity is then drawn out to form an indication that
is much more visible than the cavity itself. Liquid
penetrant testing is used to detect surface
discontinuities in solid, nonporous materials. It is
used on wrought, cast metal and metal alloys;
weldments, powdered metals, plastics, ceramics
and glass. A variety of materials and application
methods allow for some adjustment of the process
sensitivity to certain types of discontinuities,
surface conditions and material types.
Liquid penetrant testing is one of the most
widely used nondestructive testing methods in
industry. It is able to detect small discontinuities
open to the surface regardless of their orientation
or the shape of the part. With proper sequencing of
the process in manufacturing and the use of
appropriate cleaning methods with trained and
certified operators, liquid penetrant testing is a very
reliable, accurate and effective surface inspection
process.
Advantages of the Penetrant Process
The following are advantages of the liquid
penetrant process:
1. very small surface discontinuities can be
detected,
2. a wide variety(sự đa dạng) of materials can be
tested,
3. complex geometrical shapes can be inspected in
a single operation,
4. various sensitivities and processing methods are
available,
5. it is relatively (tương đối)easy to use,
6. it can be portable(xách tay, di chuyển được),
and
7. when compared to other testing methods, it has
a low cost.
Disadvantages of the Penetrant
Process
The following are disadvantages of the liquid
penetrant process:
1. porous(xốp) materials cannot be tested;
2. surfaces must be clean and free of paint,
coatings, soil, moisture(hơi ẩm) and
contaminants;
3. it cannot be used following metal smearing
operations such as shot peening, sand blasting,
certain machining operations (unless material is
acid etched to remove smeared metal);
4. some materials (rubber and plastics) may be
adversely affected by the penetrant's petroleum
base;
5. it is very dependent on operator skill; and
6. some penetrant products use ingredients that
may cause skin irritation under prolonged
contact if proper protective clothing is not worn.
ASNT Level II Study Guide: Liquid Penetrant Testing
Basics of the Penetrant Process
The basic penetrant process can be divided into
three steps: application of the penetrant, removal of
the excess surface penetrant and development of the
indication. However, the process must be preceded
by appropriate surface preparation and cleaning
methods, parts must be dried after penetrant
removal, indications must be evaluated after
processing and parts must be cleaned after testing.
Preparation of Parts for Penetrant Testing
Final examination by the penetrant process
should be performed following all operations that
may cause or expose discontinuities on the part
surface. Examples of these operations are heat
treating, machining, welding, bending and
straightening.
The penetrant process should be performed
before any treatments that smear the surface of the
part such as: honing, lapping, sanding, deburring,
sand blasting or vapor honing. If these types of
operations have been performed, the parts must be
chemically etched before the penetrant process in
order to obtain any meaningful results.
Penetrant inspection also should be performed
before operations such as peening, plating, painting,
anodizing, or any other surface coating operations.
Surface Condition
The surface condition of a part must be evaluated
before the penetrant process begins. The condition
of the surface plays a critical role in the success or
failure of the liquid penetrant test to form an
indication from a discontinuity.
Coatings such as paint and plating interfere with
the penetrant's ability to enter a discontinuity by
covering or filling the cavity. Indications produced
on coated surfaces are generally from
discontinuities in the paint or plating rather than
those in the base material. Anodized coatings are
very porous. Absorption of the penetrant can mask
discontinuities by making relevant indications
indistinguishable from the anodized surface of the
part.
Operations that deform the surface, such as
grinding, cutting, shot peening, sand blasting and
vapor honing, can cover discontinuities by smearing
a thin layer of metal over the opening, reducing its
size or sealing it completely. Because liquid
penetrant testing cannot detect anything not open to
the surface, this thin coating of metal prevents the
penetrant liquid from entering the cavity and
forming an indication. These operations also can
cause discontinuities in the material and performing
the liquid penetrant test before the metal smearing
operation is not always an option. In such cases, the
material should be chemically etched following the
mechanical operation and before the liquid
penetrant test.
The most common surface condition that
adversely affects the liquid penetrant testing process
is the presence of contaminants such as oils, grease,
dirt, rust, scale, carbon deposits or others. These
materials may prevent the penetrant from entering
the discontinuity, absorb the penetrant and mask
indications, or chemically react with the penetrant
materials reducing the penetrant's effectiveness.
Precleaning of components using the appropriate
method before liquid penetrant testing is critical.
Table 1.1 lists common contaminants that affect the
penetrant process.
Recommended reading
Subject
Reference*
history of liquid penetrant testing
A,B,C
basic principles of liquid penetrant testing
A,B,C
advantages and disadvantages of liquid penetrant testing
A,B,C
*See introduction for explanation of references.
Penetrant System
Liquid penetrant testing is defined by the
materials used to perform the process. The
variations in the testing process produce several
system sensitivities and types of penetrants.
System Sensitivity
The sensitivity of a system is defined as a
measure of the smallest discontinuity that will
produce a discernible indication. The sensitivity of
a system must meet the needs of the
circumstances. If a system is too sensitive, the
results may be misleading and time will be wasted
in the evaluation process. If the system is not
sensitive enough, rejectable defects could remain
undetected. The cost of materials can be directly
related to system sensitivity and the use of a
sensitivity higher than required would increase the
cost unnecessarily.
The appropriate liquid penetrant testing system
is determined by considering the following:
1. governing standard or specification - certain
industries require specific penetrant methods,
or specify restrictions on the materials that
may be used;
2. surface condition and the type of
discontinuities associated with the part - rough
surfaces, threads, keyways, internal cavities,
wide, shallow or tight crack discontinuities are
conditions that can affect the optimum choice
for a penetrant system; and
3
3.
location, size of the part, quantity and
coverage required - field inspections are most
often performed with solvent removable visible
dye and nonaqueous developer because of
portability and no special lighting is needed.
Type of Penetrant
Penetrant can be fluorescent, visible or dual
mode dye that has both visible and fluorescent
properties.
Fluorescent penetrant is further defined by a
sensitivity level category. The sensitivity of a
penetrant is related to the brightness of an
indication when measured with a photometer and
compared to a standard. There are five levels of
sensitivity for fluorescent dyes:
1. Level 1/2: ultralow sensitivity,
2. Level 1: low sensitivity,
3. Level 2: medium sensitivity,
4. Level 3: high sensitivity, and
5. Level 4: ultrahigh sensitivity.
Fluorescent penetrant contains a dye that is
visible under UV-A light. To view the indications,
inspection is performed in a darkened area with an
ultraviolet light source.
Visible penetrant uses a red, orange or purple
dye that is highly visible when contrasted against a
white developer coating the part surface. Inspection
must be performed under white light.
Table 1.1: Precleaning
Contaminant
Carbon, varnish
Heavy oils
Light oils
Oil with solid particles
Paint
Penetrant material residue
Scale, oxide, corrosion
Smeared metal
Effects on the Penetrant Process
Bridge/fill voids, produce residual
background, cause false indications
Fill voids, fluoresce
Fill voids, fluoresce
Fill voids, fluoresce, cause false indications
Bridge voids, produce residual background,
cause false indications
Fill voids, interfere with indication formation
Bridge/fill voids, produce residual
background, cause false indications
Bridge/fill voids
ASNT Level II Study Guide: Liquid Penetrant Testing
Dual mode penetrants contain dyes that are both
colored under white light and fluorescent under
ultraviolet light. However, the intensities are less
than the single mode penetrants.
Tables 1.2 and 1.3 compare the types of
penetrant and sensitivities.
Advantages of Fluorescent Liquid Penetrants
Fluorescent indications viewed in a dark test
booth are more readily seen than indications
produced by visible dye liquid penetrants under
normal light conditions. This is especially true in
the case of liquid penetrant indications of minute
cracks or pinholes. Because fluorescent liquid
penetrant indications are more visible, it is
generally accepted that fluorescent liquid penetrant
testing is more sensitive to small discontinuities
than visible dye. Also, because luminous
discontinuity marks can be located easily, the
fluorescent dye lends itself to faster readout.
Aerospace industry specifications often call for
fluorescent testing of critical parts because very
small discontinuity indications must be detected
reliably.
Advantages of Visible Dye Penetrants
Though its overall performance is considered
lower and production testing of small parts is
slower, the visible dye liquid penetrant process has
some advantages of its own. It does not require a
darkened area or a source of electric power for
illumination. For this reason, it is more often used
as a portable testing tool in the shop or field. Large
test parts, difficult to move to a dark booth, can be
Table 1.2: Comparison of fluorescent penetrant sensitivity levels
Level
Primary Uses and Advantages
1/2 and 1 In process inspection - minimal
background Complex geometry
Porous surfaces
2
3
4
In process inspection
Final inspection
In process and final inspection
Sensitive to small, tight
discontinuities
In process and final inspection
Very sensitive to small, tight
discontinuities
Disadvantages
Least sensitive
May produce moderate background
on rough surfaces
High background on rough surfaces
High background on rough surfaces
Table 1.3: Comparison of penetrant types
Type
Primary Uses and Advantages
1
In process and final inspections
Wide, shallow and tight crack discontinuities
Failure analysis
2 In process inspection of surfaces machined in
further processing. Field inspections with
portable kit Localized area of large parts
Disadvantages
Requires special lighting
Requires electricity
Less sensitive than Type 1
Does not perform well for
wide, shallow
discontinuities
5
inspected where they are located with visible dye
liquid penetrants. The visible dye liquid penetrant
is widely used for inspection of weldments both in
the shop and in the field.
Selection of Liquid Penetrant Material and
Process
The techniques capable of the greatest
sensitivity are often the most costly and many tests
require the ultimate sensitivity. However, high
sensitivity is frequently not required and may even
produce misleading results.
The following factors should be considered
before deciding on the type of liquid penetrant
testing system to install and/or use:
1. composition of parts to be inspected;
1. number of parts or test areas to be inspected per
unit of time;
2. size and weight of parts to be handled;
2. location at which testing is required (that is,
receiving department, in process along a
production line, during assembly, as final
inspection, in the field during erection, at
maintenance facilities or in service);
3. types of discontinuities to be expected, for
example, porosity, cracks, seams or laps;
4. size of discontinuities to be detected (for
example, small, deep, large, shallow, clustered
or scattered);
5. surface condition of parts to be inspected (such
as as-cast, as-forged, machined, ground,
lapped, polished, plated, painted, corroded,
oily, covered with combustion, scratched or
scaled parts); and
6. condition to which parts will be subjected after
testing (for example, medical, nuclear or
oxygen systems; welding, plating or finishing
operations; high temperature, aerospace,
industrial or transportation uses; inaccessible
locations; or consumer products).
The selection may be influenced by specification
requirements, education and experience of
personnel and the quality level of test required. The
quality of the test parts to be inspected should never
be allowed to influence the quality level of testing.
The test quality is determined by the nature of test
parts and the service conditions for which they are
intended.
Fluorescent Liquid Penetrant
The regular performance water washable,
fluorescent liquid penetrant is generally more
practical for rough surface parts such as sand
castings. The higher performance liquid penetrants
are favored for inspecting forgings, machined
surfaces and more critical load carrying parts.
Visible Dye Liquid Penetrant
The selection of a visible dye liquid penetrant is
relatively uncomplicated when compared to
selecting fluorescent liquid penetrants. If the test is
to take place in the field, a portable system using a
solvent remover wipe-off technique is usually the
first choice. Selection of a visible dye liquid
penetrant is largely dependent on economic factors
and the facilities available. The visible dye liquid
penetrant class is not divided into performance
grades as is fluorescent liquid penetrants.
The visibility of the indications with respect to
the white developer background is a key factor in
successfully revealing tight discontinuities. The
visibility of colored contrast liquid penetrants
depends on the color dye concentration. Because
visible dye liquid penetrants are not categorized
with respect to visibility or performance, these dyes
are selected based on need.
Penetrant Application
Penetrant may be applied by various methods as
listed in Table 1.4. Care should be taken to ensure
complete coverage of the areas of interest,
regardless of how the penetrant is applied.
Brushing and spraying can fail to cover areas
completely and immersion can trap air and prevent
penetrant (or emulsifier when rinsing) from
contacting the part surface.
Penetrant Dwell
The total time the penetrant remains on the part
surface is the penetrant dwell. The time required for
a penetrant to enter a discontinuity is dependent on
temperature, the type of discontinuity and the
possibility of contaminants entrapped within
discontinuities. Large, shallow discontinuities
require less dwell time than small, tight cracks.
Discontinuities free from contaminants require less
dwell time than discontinuities with entrapped soil
because it is easier for the penetrant to enter them.
The standard minimum dwell is 5 min unless
testing in service parts. If service fatigue cracks are
ASNT Level II Study Guide: Liquid Penetrant Testing
suspected, the minimum dwell time required is
often 2 h, but for stress corrosion up to 4 h may be
required. When the dwell exceeds 1 h, applying
fresh penetrant every hour improves the rate of
penetration.
It is important to allow sufficient time for the
appearance of minute indications from fine
discontinuities, such as tight fatigue cracks. To use
the time required for an indication to develop as a
measure of the extent of the discontinuity, other
variables such as type of liquid penetrant,
sensitivity of technique, temperature of part, dwell
time and condition of examination must be
controlled.
Fine liquid penetrant indications usually denote
fine discontinuities, however, fine indications may
also be caused by insufficient dwell time.
Temperature
The temperature of the penetrant materials and
the part must be within an acceptable range for
processing. ASTM E 1417 specifies a temperature
range of 4 to 52 °C (40 to 125 °F).
The viscosity of most liquids, including
penetrants, increases at low temperatures. If a part
is quite cold, under 16 °C (60 °F) for example, the
liquid penetrant may become chilled and thickened
when applied, making the dwell time for very fine
discontinuities longer than for parts at higher
temperatures. If a part or liquid penetrant is too hot,
the volatile components of the liquid penetrant may
evaporate, changing the ability for revealing small
discontinuities. Material temperatures from 10 to 52
°C (50 to 125 °F) produce optimum results with
conventional liquid penetrants, however, special
penetrants developed for
aerospace and nuclear power programs can be used
in extremely cold or relatively high temperatures.
Penetrant Removal Method
Excess penetrant is removed by water wash,
hydrophilic emulsification, lipophilic
emulsification, or solvent wipe.
The penetrant must be removed from the part
surface without removing it from within a
discontinuity. An optimum amount of removal must
be obtained. Too little removal will cause an
excessive penetrant background and indications will
be indistinguishable from the part surface. If too
much is removed from the discontinuity, a weak
indication or no indication will be formed. The
methods for removing surface penetrant and the
SAE AMS 2644 designation are:
1. Method A - Water Washable
2. Method B - Lipophilic Emulsifier
3. Method C - Solvent Removable
4. Method D - Hydrophilic Emulsifier
Fluorescent penetrant should be removed in a
darkened area equipped with ultraviolet lighting
regardless of the removal method.
Table 1.5 lists the advantages and disadvantages
of the various removal methods.
Water Washable (Method A)
Water washable penetrants contain emulsifying
agents that make the oil miscible (mixable) with
water. The penetrant may be removed with a manual
or automatic coarse water spray, by immersion in an
air agitated water wash or by manually wiping.
Table 1.4: Penetrant application
Type of
Penetrant
AMS-2644
Designation
Fluorescent
1
Visible
2
Dual mode
Method of
Application*
Spray, dip,
brush,
Spray, dip,
brush
Spray, dip,
brush
Dwell Time
Min./Max.
Lighting
Required
10min/2h
Ultraviolet
10min/2h
Visible
10 min/2 h
Visible/
Ultraviolet
* Spray may be manual, pressurized or electrostatic.
7
The size of the droplets, pressure, temperature
and angle of a water spray rinse can affect removal
of the penetrant. Most industry and military
specifications limit acceptable water temperature to
10 to 38 °C (50 to 100 °F) at a pressure not to
exceed 276 kPa (40 psi). The spray nozzle should
be a minimum of 30 cm (12 in.) from the part at an
angle between 45 and 70 degrees.
An air agitated immersion rinse is a removal
method that must maintain adequate water
circulation and air agitation. Experiments to
determine the amount of rinsing required for
specific processes should be performed before the
actual inspection. The water temperature
requirements are the same as for the water spray
method.
The rinsing operation must be monitored
closely to avoid overwashing. Washing should be
stopped as soon as an acceptable background level
is observed.
Lipophilic Emulsifier (Method B)
Removal is performed by introducing an
oilbased emulsifier as a separate process step.
Lipophilic emulsifier diffuses in to the surface
penetrant. It is usually applied by immersion;
brushing or wiping may cause streaking due to
uneven emulsification and are not recommended.
This system offers more control and has fewer
problems with over and under washing compared
to the water washable method. The emulsifier
dwell may be anywhere between 5 s up to 5 min.
Table 1.5: Method of removal
Remover
Material
Water
AMS-2644
Designation
A
Lipophilic
Emulsifier
B
Solvent
C
Hydrophilic
Emulsifier
D
Advantages and
Primary Uses
Fewer processing steps
Reduced processing time
Lower cost
Elimination of the
emulsifier station
Wide, shallow
discontinuities
Supplied ready for use
Portable
Localized areas, field
applications
Wash station not required
Small, tight discontinuities
Wide, shallow
discontinuities
Post rinse time less critical
Reduced background on
rough surfaces
Emulsifier touchup during
final rinse
Disadvantages
No control of emulsifier
Critical rinse time
Effects of water
contamination
Extra processing steps
Critical rinse time
Poor results on rough surfaces
Water and penetrant
contamination
Over-removal of penetrant
Time consuming for large
parts or high volume
May be flammable
Extra processing steps
Must maintain concentration
levels
Contamination from penetrant
8
ASTM E 1417 limits lipophilic emulsifiers to a 3
min maximum dwell time. Finding the optimum
time for specific conditions is generally
accomplished through experimentation. Experience
under similar circumstances related to the type and
size of suspected defects, surface roughness of the
part, temperature of materials, water contamination
levels of the penetrant and emulsifier can be used
for a guideline. If the emulsification time is either
too short or too long, the part must be entirely
cleaned and reprocessed with an adjusted emulsifier
dwell.
Following the appropriate dwell, the part should
be quickly sprayed with water wash to stop the
diffusion process. Once the diffusion process is
halted, the emulsified penetrant is rinsed using the
same methods as the water washable method.
Solvent Removable (Method C)
Solvent remover is usually supplied in aerosol
spray cans. The solvent works by diluting the
surface penetrant. The part is first wiped with clean,
dry, lintfree cloths or towels. After the major
portion of penetrant has been wiped from the
surface, the surface should be wiped with a clean
cloth, lightly sprayed with solvent, until just a trace
of penetrant is observed on the cloth. Extreme
caution must be used to avoid excessive removal.
Hydrophilic Emulsifier (Method D)
This process is similar to method B except that
the emulsifier is waterbased and uses detergent
action rather than diffusion to remove the surface
penetrant. Emulsification of the penetrant within a
discontinuity is less likely to occur with hydrophilic
emulsifier than with lipophilic emulsifier. This
allows complete removal of surface penetrant and
improves contrast for inspection. Prerinsing the part
following the penetrant dwell is recommended for
hydrophilic emulsification processing. The prerinse
is performed using the water spray techniques
described for water washable penetrant. Prerinsing
should be held to the minimum time required to
remove the bulk of surface penetrant. Immediately
following the prerinse, the hydrophilic emulsifier
should be applied by spraying or immersing.
Agitation of the emulsifier is required to produce
the detergent (scrubbing) action that removes the
penetrant. The optimum emulsification time must be
determined through experimentation for the
particular application. The emulsifier concentration
for spray methods is limited to 5%. Immersion
method concentration levels can vary from 5% to
35% depending on the manufacturer. Do not exceed
the concentration levels suggested by the
manufacturer. The emulsifier dwell time should not
exceed 2 min.
Drying
The need to dry parts after penetrant removal
depends on the removal method used and the type
of developer that will be applied. When dry or
nonaqueous developer is used, parts are dried before
the developer is applied. When aqueous developer
is used (water soluble and water suspended), parts
are dried after the developer is applied.
For water washable and emulsified applications,
parts are dried at room temperature or in a
recirculating forced air oven. Parts should be rotated
during drying and pools of water should be
removed. Oven drying time should not be any
longer than the minimum time necessary to dry the
part. Oven temperature should never exceed that
specified in the written procedure or in ASTM E
1417(71 °C or 160 °F).
Develop the Indication
An indication may be selfdeveloped, where the
penetrant seeps to the surface after the excess is
removed. Development is normally enhanced with a
developing agent. Developer is available in dry,
water soluble, water suspended or solvent
suspended forms. Developers are described in more
detail starting on page 15.
Inspection
A vital part of the liquid penetrant testing process
is the evaluation of the results. Indications must be
reviewed for their relationship to discontinuities in
the material. Consideration must be given to the type
of material, size, shape and processing history of the
part that is being inspected. Processing history
includes information specific to the part and may
include forming, casting, welding, machining, heat
treating or other manufacturing operations.
9
When properly performed, the penetrant process
will provide visible indications at all relevant
surface discontinuities.
Importance of the Inspector's Evaluation
Inspector training and experience are necessary
for determining the relevancy of an indication.
Evaluating indications correctly is a skill learned
by working with experienced inspectors and
observing the interpretation process until sufficient
knowledge is gained. Effective evaluation cannot
be mastered from classroom training alone.
In some mass inspection operations, the person
who operates the test equipment merely segregates
the parts that show indications. Others decide their
disposition. In most cases, however, the inspector
who first sees the indication is also expected to
interpret it.
Skill and proficiency in developing and then
interpreting indications must be acquired by
experience. A skilled and experienced inspector can
add greatly to the effectiveness of liquid penetrant
testing.
The inspector must also know the materials
under test: what they are, how they are made and
how they have been processed. In addition, the
inspector must understand what types of
discontinuities may be introduced during
manufacturing and processing. Inspectors who
know what discontinuities to look for and where
they are likely to occur are able to select the best
techniques available for their detection.
Penetrant Inspection Documents
Penetrant testing is conducted with a specific
technique in accordance with a written procedure.
The technique defines the process variables (dwell,
emulsification, etc.) specifically for the part being
inspected. The technique should reference the
acceptance criteria as per contract, engineering
drawing, specification or standard.
The procedure is a general inspection instruction
that defines the materials, equipment, cleaning and
process methods that may be used. It defines the
minimum and maximum times, temperatures,
pressures, etc., for each step in the penetrant
process. Requirements for personnel qualification
and certification are also defined.
Procedures are based on the requirements of
industry or military specifications, standards or
codes. These specifications define the requirements
for personnel, materials, processing methods and/or
acceptance criteria. Examples include ASTM E
165, ASTM E 1417, MIL-STD-6866, MIL-STD271, MIL-STD-410, NAV-SEA 250-1500 and
ASME Boiler and Pressure Vessel Code, Section
V.
Acceptance criteria generally indicate the
maximum size of allowable indications. They may
define a total number or a total area for acceptable
indications over a specified surface area of a part. A
minimum distance for separation between rounded
indications may also be defined based on the size of
the largest indication. Weldments and castings are
often photographed for use as accept and reject
examples of various types of indications. These
reference standards also assist in determining the
type of discontinuity that caused the indication.
Visual Requirements
Penetrant inspection standards and specifications
have minimum requirements for an inspector's
visual acuity and color perception. Visual acuity
(the ability to resolve details) decreases as light
levels decrease. The ability to distinguish between
colors is necessary to locate indications. An
individual with red-green color blindness may not
be able to distinguish indications at various levels
of brightness because of the penetrant's colors.
Fluorescent penetrant inspection requires an
inspector to allow for visual adjustment to the
darkened area. Eyes become adapted to the dark
after approximately 5 min.
Periodic eye examinations by qualified medical
personnel are recommended for those involved in
the interpretation of penetrant indications.
Classification of Discontinuities by Origin
There are three times during the life of a part
where discontinuities can be introduced. They may
exist in the raw material, they may result from
forming and machining, or they may be caused by
service conditions. Table 1.6 lists common
discontinuities that can be detected with penetrant
inspection. This classification is as follows.
1. Inherent discontinuities are introduced into the
basic materials as the result of its initial
production from ore to raw components up to
the point where it is ready for initial processing.
Inherent discontinuities can form during the
solidification process of molten metals in
10
ASNT Level II Study Guide: Liquid Penetrant Testing
castings and ingots. Welding produces many of
the same discontinuities when the metal
becomes molten and flows during the process.
Discontinuities occur when the material, or a
portion thereof, cools too slowly or too fast, is
subjected to localized moisture or other
material that creates gas pressure buildup, or
develops internal stresses after solidification.
Processing or forming discontinuities fall into
two groups: (a) discontinuities introduced
during primary processes, such as casting,
rolling, forging, drawing, welding, etc. and (b)
discontinuities introduced during finishing
processing, such as machining, heat treating,
grinding, plating, etc. Forming operations that
involve hot and cold working can produce new
discontinuities or alter the appearance of
existing discontinuities. Machining can expose
subsurface discontinuities or contribute to the
formation of new discontinuities during grinding,
lapping, milling, cutting and lathing operations. 3.
Service discontinuities develop as the result of the
material or part being in service. This group
includes fatigue from repetitive cyclic loads,
service loads, corrosion, residual stress and stress
corrosion.
Identifying Indications
Indications as small as 0.4 mm (0.015 in.) may
be considered relevant and may affect the
serviceability of a part. Inspection may result in
multiple indications being observed that must be
Table 1.6: Types of discontinuities
Discontinuity
Product
Burst
Center bead crack
Forge
Weld
Cold shut
Crater crack
Fatigue crack
Fold
Grinding crack
Heat affected zone
(HAZ) crack
Hot tear
Inclusion
Lack of fusion or
penetration
Lamination
Lap
Microshrinkage
Pipe
Porosity
Quench crack
Shrinkage crack
Stress corrosion crack
Cast
Weld
Service related
Cast
Any form machined
Weld (in the base
metal)
Cast
All
Weld
Forge, roll
Forge
Cast
Forge
Cast, weld
Any form heat treated
Cast
Service related
Appearance
Broad starburst
Continuous/intermittent linear,
tight, or open
Half moon to linear, smooth
Starburst
Continuous linear, tight, or open
L/I, L/C, tight
Linear, tight, random multiple
Linear, tight, emanating from weld
Linear, tight or open
Near-rounded
Linear parallel to weld
Linear, tight
Linear, tight
Round, porous
Linear, tight
Round, randomly dispersed
Linear, tight or open
Linear emanating from void
Linear, tight or wide
11
determined to be relevant or nonrelevant and
interpreted as acceptable or rejectable. According
to ASTM 1316, a relevant indication is "an NDT
indication that is caused by a condition or type of
discontinuity that requires evaluation." The
relevancy of an indication is determined by the
inspector's judgment alone. The acceptance or
rejection of relevant indications is determined by
criteria specified on the part drawing, in referenced
inspection specifications or standards, or in a
contractual agreement.
Relevant indications are the result of penetrant
bleedout from an unintentional change or
discontinuity on the part surface. Relevant
indications must be evaluated for size, location and
type according to the specified acceptance criteria
to determine if the discontinuity is cause for
rejection of the part. No all discontinuities are
necessarily cause for rejection.
According to ASTM 1316, a nonrelevant
indication is "an NDT indication that is caused by a
condition or type of discontinuity that is not
rejectable. False indications are nonrelevant."
Nonrelevant indications can be caused by
intentional changes of the part surface. Sheet metal
fittings, rolled flanges, threads and splines are
examples of features inherent in a part's design that
may form nonrelevant indications.
According to ASTM 1316, a false indication is
"an NDT indication that is interpreted to be caused
by a discontinuity at a location where no
discontinuity exists." False indications are often
caused when penetrant comes into contact with the
part after processing. Penetrant on the inspection
table surface or on the operator's hands can create
false indications. False and nonrelevant indications
may potentially mask relevant indications.
Cleaning and reprocessing a part for inspection is
required when false indications are noted.
Postcleaning
Residue from the penetrant process can be
harmful to the part during further processing or the
service of a part. It can also interfere with future
penetrant inspections. Penetrants remaining on a
part may adversely affect plating, anodizing and
welding operations. Residual oils on liquid oxygen
system components can result in an explosion.
Penetrant remaining in discontinuities can dry or
disrupt the mechanics of penetrant in later
inspections. Developers may act as an abrasive
when left on contact areas of moving parts, they
can absorb moisture and cause corrosion, and they
may absorb penetrant in subsequent processing
masking indications or creating a high residual
background. Developers become harder to remove
with time. Most developers can be removed with
water and wiping or by scrubbing.
Recommended reading
Subject
Reference*
surface condition, cleaning
A, B, C
penetrant application removal
A, B, C
drying__________________________
A, B,C
inspection
________________________________
visual requirements
________________________________
identifying indications
________________________________
formation of discontinuities
________________________________
post cleaning
__________________
A, B,C
*See Introduction for explanation of references.
A, B, C
B,C A,
B,C A, B,
C A, B, C
Chapter 2
Penetrants, Developer and Equipment
Penetrants
Characteristics of Penetrants
To detect discontinuities, the penetrant must coat
the area of interest in a continuous and uniform
manner and must migrate into small cavities that
are open to the surface. These cavities are generally
invisible to the naked eye.
Surface tension, wetting ability and capillary
action are the mechanisms that enable a liquid to
perform well as a penetrant material. Light oils are
generally used for penetrants because of these
characteristics.
Surface Tension
Molecules of a liquid are subjected to the
attraction of surrounding molecules. The attraction
of like molecules is called cohesion. This attraction
has no effect at the interior of the liquid because the
force is equalized by the attraction from all
directions. However, molecules at the surface are
pulled back toward the interior of the liquid by the
molecules below. This contraction of the surface
creates what is called surface tension. As the
cohesive force increases, the surface tension also
increases.
Wetting Ability
The attraction of dissimilar molecules is called
adhesion. If the adhesive force between a liquid
and a surrounding solid is weaker than the
14
cohesive force of the liquid, the liquid will contract
and pull away from the surface, forming a contact
angle greater than 90 degrees. If the adhesive force
is stronger than the cohesive force, the liquid will
flow and adhere to the solid to a point where the
adhesive and cohesive forces are equalized in the
liquid. If the liquid forms an angle of less than 90
degrees to the surface, the individual droplets will
merge into a uniform coating wetting the surface
(Figure 2.1).
Capillary Action
Capillary action is easily illustrated by inserting
a capillary tube into a clear container of liquid.
Inside the tube, a liquid with high surface tension
will rise above the liquid level outside of the tube.
The low contact angle causes the liquid to curve up
the tube wall while the surface tension pulls the
liquid downward at the center of the liquid. These
forces working together create capillary rise (Figure
2.2a). A liquid that does not have sufficient wetting
ability will keep the liquid inside the tube below the
level outside (Figure 2.2b), or at the same level
(Figure 2.2c).
Capillary rise enables the penetrant to enter
discontinuities. A discontinuity acts like a capillary
tube and the ability of a penetrant to climb the walls
of a discontinuity is the mechanism used to enter the
discontinuity. Capillary rise will occur even though
the discontinuity is not open on both ends like the
tube. The penetrant will not completely fill the
cavity due to trapped air, which
ASNT Level II Study Guide: Liquid Penetrant Testing
will exert an outward force on the penetrant
(Figure 2.3).
Specific Gravity
Physical Properties of Penetrants
Physical properties of penetrants include
viscosity, volatility, specific gravity, flash point and
thermal stability.
Viscosity
Viscosity measures the flow rate of a liquid.
Higher viscosity liquids flow more slowly than less
viscous liquids. Increasing the temperature of a
liquid lowers its viscosity. Viscosity does not affect
the ability of the penetrant to enter a discontinuity;
however, the viscosity of a penetrant does affect the
rate of penetration and the penetrant dwell time.
Penetrants with a higher viscosity will require
longer dwell times than less viscous penetrants.
Volatility
Volatility indicates the boiling point of a liquid.
Low volatility means a high boiling point. Highly
volatile liquids are not desirable for penetrants
because of their rapid evaporation, which results in
the drying of the penetrant on a part during the
dwell and the loss of penetrant materials in open
tanks.
The ratio of a liquid's density to that of distilled
water is the liquid's specific gravity. A penetrant's
specific gravity may be less than 1 if it has an oil
base.
Flash Point
The temperature at which a liquid's vapors
become flammable when a source of ignition is
present is called its flash point. The flash point
does not affect the performance of a penetrant but
it is considered for safety reasons.
Thermal Stability
Thermal stability is related to the tendency of
some dyes used in penetrant materials to lose their
brightness or color when exposed to elevated
temperatures for an extended time. This loss of
color is referred to as heat fade. The ability of a
penetrant to resist this loss is its thermal stability.
Chemical Properties of Penetrants
Inertness
Penetrant processing materials must be inert to
the material composition of the part being
processed. Nickel based alloys, titanium and
austenitic stainless steels are susceptible to
hydrogen embrittlement and intergranular
Figure 2.2: Contact angle in a capillary tube
Capillary Tubes
Chapter 2, Penetrant Characteristics
corrosion from small amounts of sulfur and
halogen residues. Nuclear and pressure vessel
codes limit the sulfur or chlorine residual content
to 1 % by weight maximum because of their
extensive use of these metals and the risks
involved with any system failure.
Removability
Removability is the ease with which excess
surface penetrant is sufficiently removed without
removing it from discontinuities. Good
removability is critical for reducing or eliminating
residual background.
15
4. form d, nonaqueous developer Type I,
5. form e, nonaqueous developer Type II,
6. specific application developer.
Table 2.1 compares the various developers.
Figure 2.3: Penetrant over
discontinuity
Penetrant
Discontinuity
Water Tolerance
Water washable penetrants must be capable of
tolerating a certain amount of water contamination.
Developer
Penetrant remaining in a discontinuity is drawn
out by the same capillary forces that draw it into
the cavity. The adhesive force between the
penetrant liquid and the solid surface will cause the
penetrant to be drawn back out of the discontinuity.
The cohesive force of the liquid will stop its rise
out of the discontinuity at the point where it is
balanced by the adhesive force.
If the discontinuity is large, the penetrant drawn
to the surface is visible without further processing.
Developer is applied to aid the detection of smaller
discontinuities. Developers provide an absorbent
surface containing fine capillary paths that assist in
drawing penetrant out of a discontinuity. This
provides a much larger penetrant indication surface
area (Figure 2.4). Observation of indications is
further enhanced by the contrasting background
that the developer provides.
The following are types of developers:
1. form a, dry powder developer,
2. form b, water soluble developer,
3. form c, water suspendible developer,
Figure 2.4: Developer
enhancement of discontinuity
Penetrant
Developer
Discontinuity
Recommended reading
Subject
Reference*
penetrant properties
B,C
systems
C
"See Introduction for explanation of references.
16
Dry Powder
Water Soluble
Dry developer is a light, fluffy powder that
clings to the part in a fine film. Dry developer is
easy to use and has good development properties for
fluorescent penetrant. Under ultraviolet light, metal
surfaces appear deep violet in color, which contrasts
well with the bright yellow-green fluorescence of
the penetrant. Dry developer does not interfere with
this contrast because it dusts the surface lightly but
does not coat it. It does not work well for visible
penetrant because it does not provide a contrasting
background. If dry developer becomes wet,
clumping may occur. Clumping limits or eliminates
the developer's capillary action. Dry developer in
tanks may become fluorescent if it is recycled
excessively. Fluorescent specks or particles may
cause false indications. Dry developer in a powder
bulb is often kept in the inspection area and applied
to a part surface that has been wiped during
evaluation.
This type of aqueous developer is dissolved in
water and forms a translucent film. Water soluble
developer can be used for fluorescent dyes, but it is
not recommended for use with visible dye or the
water washable removal method. Water in the
developer may remove water washable penetrant
from discontinuities. Water soluble developer can
save time during processing because drying is
included in the developer dwell time. Water soluble
developer is supplied as a dry concentrate that must
be mixed and maintained at the proper ratio of
developer to water. The developer should be
checked at regular intervals for penetrant
contamination and water evaporation.
Water Suspendible
Water suspendible developer is supplied as a dry
concentrate that must be mixed and maintained at
the proper ratio of developer to water. Suspended
aqueous developer does not dissolve in water so it
must be thoroughly agitated just before application
Table 2.1: Developer types
Material Form/
AMS-2644
Designation
Dry powder
Method of
Application
Dust/fog, dip,
Application
Sequence
1/2
Easy to use
Penetrant
dwell to
4h
1/2
Penetrant
dwell to
2h
Easy to remove
Good for Type I
Water soluble
Spray, flow,
dip
Before drying
Water suspendible
Spray, flow,
dip
Before drying
Spray
Advantages and
Primary Uses
After drying
spray
Nonaqueous
Type I and Type 11
Dwell
Time
After drying
1/2.
Penetrant
dwell to 2h
10 min to
1h
Disadvantages
Not for Type II
Parts must dry first
Penetrant
contaminated
Needs no
Acts as detergent
agitation
Not for Method A
Easy to remove
Not for Type II
Applies thin coat
Bacteria/fungus
Evaporation
Visible'coating , Critical immersion
Surface contact
Frequent agitation
Most sensitive
High contrast
Portable
Bacteria/fungus
Difficult to remove
Expensive
Flammable Not for
large areas Frequent
agitation Parts must
dry first
17
to suspend the particles in water. The development
of indications does not begin until the moisture is
completely evaporated from the developer. The
thickness of the coating and its white color work
well with visible dyes. Parts should be checked to
ensure a uniform coating of developer has been
applied. The developer should be checked at
regular intervals for penetrant contamination and
water evaporation.
Nonaqueous
Nonaqueous solvent suspended developer is
supplied in bulk containers and in aerosol spray
cans. It may be used for all penetrant types and
methods. This type of developer is applied after
drying and is considered to be the most sensitive
developer method available. When nonaqueous
developer is supplied in aerosol spray cans, process
controls are not required, but to ensure the proper
coat of developer, it is necessary to shake the can
to be sure the developer particles are resuspended.
When the developer is supplied in bulk, it is
important that the suspension be thoroughly mixed
before use. The developer must be thoroughly
agitated before spraying and should
be applied in a thin, uniform coat. The spray does
not cover larger surfaces quickly and each part
must be separately sprayed while the developer is
constantly agitated. A consistent, even coating of
developer should be maintained.
Special Application
Special application developers are designed for
use with only specified penetrant materials and
must be qualified with a particular penetrant
system. An example would be qualification of a
specific manufacturer's visible dye with a dry
developer.
Material and Process Control
Tests
Successful penetrant processing relies on
properly functioning material and equipment.
Process system variables of time, temperature and
pressure along with material concentration,
contamination, consistency, etc., must be verified
as acceptable at regular intervals. Equipment used
for verification may also require scheduled
Table 2.2: Typical equipment calibration
Equipment
Temperature gage
Pressure gage
Timers
White light meter
Ultraviolet light
meter
Refractometer
Temperature gage
Measuring
equipment
Calibration
Tolerance
Spray water rinse/wash station ±1 °C at 21 °C
(±2 °F at 70 °F)
Spray water rinse/wash station ±2% of scale
Penetrant, emulsifier, rinse,
±1 s at 10 min
dry stations
Type 2 lighting/ambient light
±10% of scale
for Type 1
Ultraviolet light intensity
±10% of scale
Where Used
Hydrophilic emulsifier
concentration
Drying oven
Inspection booth — measuring
indications
Item
3 months
3 months
3 months
6 months
6 months
±2% of scale
1 year
±5.6 °C at 66 °C
(±10°F at 150 °F)
±0.1 % of scale
6 months
1 year
18
calibration. Tables 2.2 and 2.3 contain standard
process control requirements and equipment
calibration.
Ultraviolet light intensity, emulsifier
concentration, ambient white light intensity and
penetrant area cleanliness are examples of typical
process controls that may be specified in the
penetrant inspection procedure.
Table 2.3: Typical process control requirements
Process Element
Water wash pressure
Water wash
temperature
Oven temperature
Systems performance
System
Requirement
Method A, B, D 276 kPa (40 psi) maximum
Method A, B, D 10 to 38 °C (50 to 100°F)
Item
Each shift
Each shift
Method A, B, D 71 °C (160°F) maximum
meet minimum code
All
requirements
Ultraviolet intensity
Type 1
1,000 (J.W/cm2 minimum at
part surface
1,076 lx (100 ftc) minimum
White light intensity
Type 2
at part surface
Ambient light intensity Type 1
20 lx (2 ftc) maximum at
part surface
no fluorescent
Area cleanliness
Type 1
contamination
Method B
<5%
Lipophilic emulsifier
water content
immersion: < than specified
Method D
Hydrophilic emulsifier
on the AMS-2644 QPL,
concentration
spray < 5%
check concentration with
Aqueous developer
hydrometer
Dry developer
no fluorescent
condition
contamination (fluffy not
caked)
Fluorescent brightness Type 1
>90% of unused material
sample
Penetrant water content Method A
<5%
comparison to unused
Penetrant removability Method A
material sample
comparison to unused
Penetrant sensitivity
All
material sample
Each shiftDaily
Daily
Daily
Weekly
Daily
Monthly
Weekly
Weekly
Daily
Quarterly
Monthly
Monthly
Weekly
19
Ultraviolet Light Intensity
Intensity of the ultraviolet light in the inspection
booth is checked with a calibrated ultraviolet light
intensity meter. Ultraviolet light intensity should be
1000 (iW/cm2 minimum at the part surface.
Emulsifier Concentration
To check emulsifier concentration (refractive
method) of hydrophilic postemulsifiable penetrant
systems the following procedure should be used:
1. Lift the refractometer cover plate to expose the
prism.
2. Use the plastic dip stick supplied with the
instrument to spread a small amount of
emulsifier over the prism surface.
3. Close the cover plate and point the instrument
toward a light source. Look through the
eyepiece and take the reading at the point where
the dividing line between light and dark crosses
the scale. (Tilting the instrument with respect to
the light source may be required to obtain
optimum contrast between light and dark
boundary.)
4. Clean the instrument after each use. Wipe the
prism and cover plate with a soft cloth or tissue
paper moistened with water, then wipe dry. If
the prism surface and cover plate are not well
cleaned before the next use erroneous or fuzzy
readings may result.
Ambient White Light Intensity
The ambient white light intensity in the darkened
inspection booth is verified by the use of a white
light meter. The ambient white light intensity
should not exceed 22 lx (2 ftc) at the inspection
surface.
Penetrant Inspection Area
Cleanliness
The cleanliness of the inspection booth is
checked for any contamination of fluorescent
penetrant, developer powder or other residue that
could affect the interpretation.
Penetrant Materials Testing
Water Content
Water washable penetrants are analyzed for
water content each month or any time stratification
or cloudiness is noted. Water content should not
exceed 5% by volume.
Separation of Constituents and Loss of
Fluorescence
Penetrants shall be compared with unused
samples for separation of constituents and loss of
fluorescence each month or whenever stratification
or cloudiness is noted. Separation and loss of
fluorescent brightness or cloudiness shall not be
permitted.
Washability
The washability of penetrants shall be
determined each month. Materials not passing the
washability test shall be discarded and replaced
with fresh material.
Sensitivity Comparison
Penetrants shall have a sensitivity comparison
performed each month. The sensitivity of penetrant
samples shall be comparable to the unused
reference sample.
Penetrant System Monitor
The testing and monitoring panel (Figure 2.5) is
a commonly used reference standard for monitoring
the overall performance of the penetrant system. It
is processed through all stations of the penetrant
production line to verify that all aspects of the
process (dwell time, temperatures, removal,
lighting, drying, developing, etc.) are functioning
together.
The following is typical of procedure
requirements for processing the panel:
1. Ensure the panel is dry.
2. Examine under ultraviolet light for residual
penetrant. Residual fluorescence shall be cause
for cleaning or replacement.
3. Process the panel per standard procedure and
production technique using minimum process
times.
4. Examine the processed panel under ultraviolet
light. Compare results to the correspondingly
20
ASNT Level II Study Guide: Liquid Penetrant Testing
numbered reference photograph or to previous
test results. Results shall be as follows:
a. removability: At least 75% of the grit
blasted panel surface shall show no
evidence of background fluorescence.
b. sensitivity: The minimum number of crack
indications visible shall be the same as the
reference photograph or the same as
previous test results.
5. If the system performance is unacceptable,
replace materials (for example, penetrant,
emulsifier, developer) as applicable and
recheck.
6. After completion of the test, place the panel in
an ultrasonic cleaner for at least 5 min. Store
panel until next usage in isopropanol or in a
clean dry container. Keep lid on container to
minimize evaporation.
Equipment
Penetrant processing equipment can vary from a
few spray cans and cloths to computer controlled,
fully automated systems. Table 2.4 lists materials
Figure 2.5: Testing and monitoring panel
common to portable and stationary penetrant
process lines.
Ultraviolet Lighting
Ultraviolet light is required when Type 1
(fluorescent) penetrant is used. The fluorescence of
the penetrant assists in locating small, difficult-tosee discontinuities. The most common UV-A light
consists of a mercury bulb housed with a filter that
is powered by a constant voltage transformer
producing wavelengths in the range of 320 to 400
nm. The minimum intensity of the ultraviolet light
should be 1000 uAV/cm2 at the inspection surface.
A warmup time is required for the mercury bulb to
reach full intensity and the light should remain on to
avoid cycling, which reduces the life of the bulb.
Regular cleaning of the bulb and filter is required to
remove dust, oil, dirt and fluorescent contamination
that can reduce the ultraviolet light intensity.
For remote processing when electricity is
available, portable enclosures or heavy tarps may
The testing and monitoring panel features five crack centers of different sizes for evaluating
sensitivity and includes a grit blasted section for judging wash characteristics of liquid penetrant
system: (a) drawing; (b) under white light; (c) under ultraviolet light.
(Reprinted from Nondestructive Testing Handbook, third edition: Volume 2, Liquid Penetrant Testing. Courtesy of
Boeing Company, St. Louis, MO.
Chapter 2, Penetrant Characteristics
21
be used to obtain sufficient darkness to perform
evaluations.
Stationary Processing Equipment
Requirements vary depending on the type of
penetrant and removal method used. The system
may consist of a deep sink next to a small tank of
penetrant or can be more elaborate with
electrostatic sprayers for penetrant application,
semiautomatic emulsification and/or rinse and
developer stations run by the push of a button.
Parts may be moved by hoists or conveyors,
automatically lowered and processed in emulsifier
immersion stations, or automatically processed
through a water rinse operation.
Portable Processing Equipment
Penetrant is available in kits packaged with
spray cans of penetrant, remover and developer.
They are generally a visible, solvent removable
system, but they are also available with water
washable penetrant, lipophilic emulsifier and
fluorescent penetrant. The developer is almost
always nonaqueous.
Table 2.4: Manual processing equipment
Stationary
Portable
Penetrant Application
Spray booth —• standard or electrostatic
Penetrant spray can
Immersion tanks
Brushes, cotton swabs, etc.
Dwell/drain area
Timer for penetrant dwell
Penetrant Removal
Coarse water spray
Solvent spray can
Ultraviolet light (Type 1)
Cloths/rags
White light (Type 2)
Portable ultraviolet light (Type 1)
Emulsifier tanks and/or spray apparatus
Tarp
Water rinse spray and/or tank
Water pressure and temperature gages
Timer for emulsifier dwell
Drying/Development
Hot-air recirculating oven
Developer spray can or powder bulb
Oven temperature gage
Developer dip tank, fog chamber, or spray area
Developer dwell area
Timer for developer dwell
Inspection
Ultraviolet light and darkened booth (Type 1)
Portable ultraviolet light (Type 1)
White light (Type 1 and 2)
Tarp
Magnifier, measuring devices
Magnifier, measuring devices
Solvent
Solvent
Developer powder bulb or spray can
Developer spray can or powder bulb
22
ASNT Level II Study Guide: Liquid Penetrant Testing
Automated Equipment
Fully automated liquid penetrant testing systems
process materials through cleaning, penetrant
application, dwell and removal, drying and
developer application and dwell time without an
operator. Automatic loading and unloading
capabilities also can be incorporated in some
systems. Automated systems are custom designed
for specific applications of high volume processing.
The elimination of inconsistencies in dwell and
rinse time associated with human processing is the
major advantage. The
disadvantages are the cost and inflexible nature of
the system.
Semiautomated systems may have conveyors to
move parts to the various stations where processes
are manually performed, or may include automated
emulsifier, rinse, and/or oven and developer
stations.
Automated processing ends at the inspection
area. Human inspectors are almost always required
to evaluate indications resulting from the process.
Recommended reading
Subject
developer
equipment
materials and process controls
*See Introduction for explanation of references,
Reference*
A,B,C
A,B,C
A,B
Chapter 3
Testing in Primary Metals Production
By far the largest field of application of
nondestructive tests is in the metal making industry,
including ferrous alloys and the growing list of
nonferrous metals and alloys being produced and
used. For the usual metals and alloys, there is a
considerable similarity of processes and
discontinuities that are encountered.
Producing Metals and Alloys
Iron and the nonferrous metals are refined from
their ores by a variety of processes but most of them
are ultimately produced in molten form, the molten
metal is poured into molds and allowed to solidify.
These molds may be ingot molds from which the
solidified ingot is taken through a variety of
forming processes or they may be molds for casting
the metal into final shape.
Processing Discontinuities
Discontinuities Related to Metal
Solidification
In spite of precautions to produce and solidify
metal free of foreign materials and gasses, most
metals contain nonmetallic inclusions of some
type. These inclusions may be (1) dissolved or
entrapped gasses; (2) various nonmetallic materials
such as oxides and sulfides of the metal; and
(3) finely dispersed particles of slag. Their
presence is not in itself an indication of poor
quality; this is true of steel, copper, brass,
aluminum and other metals. However, if not well
distributed or if the segregates are large, they may
be very objectionable. They will appear as stringers
or discontinuities in the final rolled or forged
product, which may seriously affect the suitability
of the metal for many purposes.
Discontinuities in Metal Ingots
Metal shrinks during solidifying and cooling.
This shrinkage may cause shrink cavities in the
center of the ingot, usually confined to the top or
last-to-freeze portion. This section of the ingot is
normally cropped and discarded. If not completely
eliminated, these types of internal discontinuities
may show up in the finished product as pipe in
rolled bars or as laminations in plate or strip.
Cracking also may occur on the surface of
ingots. These cracks are removed as completely as
possible by chipping or scarfing to prevent the
forming of seams on the finished product.
Discontinuities in Metal Castings
In the case of castings where the metal solidifies
in final form, gates and risers allow surplus metal to
form at favorable locations so that impurities can
float out of the casting proper and gas can have a
chance to escape. Porosity and gas pockets along
with slag inclusions are a major source of
discontinuities in castings and much testing focuses
on locating them. This is true of nonferrous castings
as well as steel.
Shrinkage on cooling results in thermal cracks in
castings, most often on the surface and related to
the shape of the casting. Other casting
discontinuities are hot tears and cold shuts, both
being surface discontinuities.
Vibration and external stress would cause these
cracks to become more extensive, resulting in
failure of the part. Indications of cracks are
considered a cause for rejection in almost all cases.
Cracks not only reduce the strength of a part but
they also may propagate, especially under
alternating or fatigue loads.
Discontinuities in Blooms and Billets
After being cast into ingots, a metal is then
further worked into usable form by forging, rolling
24
or pressing. A steel ingot, for example, is reheated
to the proper temperature and passed between
heavy rolls to form blooms or billets. The size of
ingots varies widely. Ingots of alloy and tool steel
may be quite small, weighing perhaps 100 kg (220
lbm), whereas ingots from which large forgings or
large thick plate are to be made may weigh many
tons. Blooms and billets are formed in an
intermediate step between the ingot and the
finished size or product.
The surface of blooms and billets may contain
seams due to rolled out ingot cracks resulting from
cooling stresses, bursts, tears, rolled-in scale or
metal particles. All of these surface imperfections
should be removed before the final finishing
operation. The surfaces of blooms and billets may
be freed of such objectionable conditions by
chipping, grinding or flame scarfing. Billets,
especially when intended for seamless tube
piercing, are often cleaned up by scaling, by taking
a cut off the surface, or by planing the surface.
Discontinuities in Hot Rolled Bars,
Shapes, Plate or Strip
Blooms and billets are often reheated to proper
working temperature and rolled into bars, shapes,
plate or strip. Seams, stringers and laminations may
appear in the finished product as a result of rolling,
forging or extrusion. The rolling operation itself
may introduce certain discontinuities, the most
common of which are laps resulting from too much
or too little metal to fill the rolls. Too rapid
reduction of cross section, especially if the metal is
at too low a temperature, may produce tears and
internal rupture called cupping.
Internal shrinkage cavities or gas pockets may
result in laminations in plate, strip, pipe, bars or
other shapes. Uneven cooling of some types of steel
may cause cooling cracks to appear in bars and
shapes.
Discontinuities in Forgings
If an ingot or billet is used for forging, a variety
of discontinuities can be produced from improper
handling of the metal under the hammer or from
working at too low a temperature. Common
discontinuities are laps and folds. Forging bursts,
both external and internal, can also occur.
In the case of die or drop forging, laps, surface
tears and bursts may be produced. In die forgings,
excess metal is forced out between the two halves
of the die forming the flash and this excess metal is
subsequently trimmed off. If not properly done,
flashline cracks or tears may be formed. Another
type of forging discontinuity is the internal rupture,
usually called flake, which occurs in the process of
cooling relatively large forgings. These may be very
severe and extremely objectionable.
Discontinuities in Rolled and Pierced
Products
In the production of seamless tubing, the billet is
pierced. Discontinuities on the inside surface of the
pierced billet may take the form of tears. Seams
may occur on the outside surface, especially if the
surface of the billet or blank had not been properly
cleaned.
Discontinuities in Extrusions
Nonferrous seamless tubing is often made by
extrusion, starting with hollow or pierced billets, or
from solid ingots. Discontinuities that occur may be
checks and tears, or imperfections may result from
uncovering internal discontinuities of the billets or
ingots. Many shapes and products are made by
various extrusion processes. Because of flow of the
metal of the original ingot during extrusion, oxide
and surface skin sometimes become folded into the
interior. A form of pipe also results from this action,
which is most objectionable when it appears in a
finished shape.
Discontinuities in Cold Worked Metal
Products
Cold rolling and cold drawing of strip, rod and
wire is a process for improving the surface finish of
steel products. Close dimensional tolerances can
thus be maintained and the metal becomes
somewhat work hardened. Die marks, scratches and
surface imperfections sometimes make their
appearance in this process. The process does not
remove seams or other discontinuities present in the
material before the cold finishing is applied.
Chapter 3, Testing in Primary Metals Production
Discontinuities in Fusion Welds
In fusion welding processes, where liquid metal
solidifies in the weld, the same sort of
discontinuities may occur as in castings — namely,
slag inclusions, gas porosity and thermal cracks. In
addition, cracking in the parent metal may occur
because of thermal stresses or as a consequence of
hydrogen pressure. There are also discontinuities
from a lack of penetration of the weld and failure to
get proper fusion of the weld metal to the parent
metal.
Discontinuities in Heat Treating
Processes
Most metal products undergo some form of heat
treatment to produce desirable physical properties.
Heat treatment discontinuities may be produced as
the result of warping or cracking. Quenching cracks
occur in steel when the process is not properly
carried out or when the design of the part or the
steel used is not adapted to the operation.
Quenching cracks are apt to appear in connection
with changes in cross section of the material that
cause excessive cooling stresses or at locations
where the contour of the surface permits stress
concentrations to occur. Sometimes hardened parts
are cracked when an attempt is made to straighten
those that have warped slightly out of shape.
Special nondestructive test techniques have
been devised for checking hardness against
specification tolerances and for unwanted
conditions such as abnormal grain size,
segregations, etc.
Discontinuities in Machined and
Ground Surfaces
Machining operations may cause surface
damage, leaving discontinuities in the form of
surface tears. Grinding of surfaces for accurate
dimensions or for finish is a common source of
surface cracking, especially on hardened steel
surfaces. Parts that have been hardened may have
residual internal stresses, produced in the
quenching process and not subsequently removed
by drawing or stress relieving. Such parts are
particularly sensitive to the formation of grinding
checks.
25
Cracks During Plating or Chemical
Treatment
Parts containing residual stresses from heat
treatment or cold working may crack during plating
processes or during the pickling that precedes
plating. Pickling etch removes some of the metal
surface containing compressive stresses, permitting
the internal tensile stress to be relieved through
cracking. Embrittlement by absorbed hydrogen
during pickling may sometimes be a factor in such
cracking.
Service Discontinuities
Fatigue Cracks
Fatigue cracking and failure resulting from
fatigue is by far the most important group of
service discontinuities. Fatigue occurs during
repeated or cyclic loading or stressing of materials.
A fatigue failure starts with a crack initiated by a
variety of causes. Under cyclic loads, this crack
progresses through the cross section of the metal
until only a small portion of the original section
remains sound. Finally failures occur even when
calculated or average stresses are far below the
elastic limit and do not depend directly on whether
the tensile strength of the metal, as determined by
static tests, is either high or low.
Significance of Surface Discontinuities
under Repeated Loading or Vibration
Fatigue cracks almost invariably start at the
surface and are initiated by conditions that bring
about locally high stresses. These stress
concentrations involve stresses above average for
the part. The stresses may, in their local area, be
above the fatigue strength of the metal. Surface
scratches, cracks or other discontinuities may cause
these local areas of high stress. Localized high
stresses may also be caused by design features of
the part — for example, high stresses occur around
holes, fillets and stiffening members.
Prevention of Fatigue Failures in Service
One of the main purposes of liquid penetrant
testing is to locate and eliminate discontinuities
likely to lead to fatigue failures. Fatigue cracking is
a serious indication sought by nondestructive
26
techniques when the machine or structure is
inspected at intervals during its service life.
Fortunately, fatigue cracks do not often propagate
so rapidly that they cannot be located early in their
existence and the part replaced before failure.
Stress Corrosion Cracking
If a part that is subject to frequent stress
reversals or fluctuations is at the same time subject
to corrosion, fatigue cracks may appear very
rapidly and may progress to failure in a very short
period of time.
Corrosion leads to service failure through
cracking of metal subject to corrosion at the same
time it is under tensile stress. Stress corrosion
cracking of steel beams around bolt holes, leading
to bridge collapse, is an example. The corrosion
allows the tension stress at the surface to be
relieved by cracking.
Other Causes of Service Damage
Other sources of service damage causing
cracking are abnormally high stresses caused by
vibration, as in steam turbine blades and jet engine
buckets; impact due to wrecks and other sudden
stoppages; and overloads due to abnormal service
conditions or simple abuse of the engine or
machine.
Recommended reading
Subject
Reference
producing metal
processing discontinuities
service discontinuities
A
A
A
* See Introduction for explanation of reference
Chapter 4
Appearance of Liquid Penetrant Indications
Several factors influence the exact appearance
of individual liquid penetrant indications.
However, there are certain general trends that hold
true for all sorts and forms of materials.
Continuous Line Indications
irregular in outline. Deep crater cracks in welds
frequently show up as rounded indications because
a large amount of liquid penetrant is entrapped and
the individual indications merge.
Porosity resulting from shrinkage cavities may
produce rounded liquid penetrant indications or
may give the appearance of cracks. Usually,
shrinkage cavities have a dendritic pattern that
helps the inspector identify them. For high stress
applications, shrinkage cavities are rejectable
discontinuities.
A crack usually shows up as a continuous linear
liquid penetrant indication. The width and
brightness of fluorescence or color depend on the
volume of the crack. The line may be fairly straight
or jagged. A cold shut on the surface of a casting
also appears as a continuous line, generally a
relatively narrow one. Because cold shuts are
caused by imperfect fusion where two streams of
metal meet but do not merge, the indication is
likely to be smooth in outline rather than jagged. A
forging lap may also cause a continuous line
indication.
Liquid penetrant indications in the form of small
dots result from a porous condition. Such
indications may denote small pin holes, excessively
coarse grains in castings, or may be caused by a
shrinkage cavity.
Intermittent Line Indications
Diffuse Indications
Many forging laps are partially welded during
subsequent blows of the forging hammer. The
liquid penetrant indication caused by such forging
laps is therefore an intermittent linear indication. A
subsurface crack that does not reach the surface for
its entire length, or a seam that is partially filled,
also produces an intermittent line indication.
Sometimes a large area presents a diffused
appearance. If fluorescent liquid penetrants are
used, the whole surface may glow feebly; if visible
dyes are used, the background may be pink instead
of white. This diffused condition may result from
very fine, widespread porosity, such as
microshrinkage in magnesium. It may also be
caused by insufficient cleaning before testing, by
incomplete removal of excess liquid penetrant, or
by too thick a coat of developer. Weak indications
extending over a wide area should be regarded with
suspicion. It is wise to repeat the test and to
eliminate any false indications, rather than to
attempt immediate evaluation of a diffused
indication.
Rounded Areas of Indications
Liquid penetrant indications of gas holes are
round blobs of rich color or fluorescence. Large gas
holes are a basis for rejection because they reduce
strength and produce a rough surface. Small gas
holes may not be rejectable discontinuities
depending on the effect on the strength of the part.
If pressure tightness or a smooth surface is
required, then even tiny pinholes are considered a
basis for rejection. The indications appear rounded
because of the volume of liquid penetrant
entrapped; the actual discontinuities may be
Small Dot Indications
Edges of Indications
The sharpness of liquid penetrant indications is
affected by the volume of liquid retained in the
discontinuity, the test conditions, such as
28
temperature and time allowed for indications to
develop, and the type of liquid penetrant used.
Generally, clear cut indications come from narrow
linear discontinuities.
Brilliance and Extent of Indications
The color or fluorescent brightness of liquid
penetrant indications can be useful in estimating
the seriousness of the discontinuity. Brightness is
directly related to the amount of penetrant present
and therefore to the size of the discontinuity. It is
difficult for the human eye to detect slight
differences in color of dye or brilliance of
fluorescence. Fortunately, larger discontinuities
usually produce larger indications in addition to
increased brightness.
Persistence of Indications
One good way to estimate the size of a
discontinuity is by the persistence of the indication.
If it reappears after the developer has been removed
and reapplied, there must be a reservoir of liquid
penetrant present. Where faint or weak indications
leave some doubt as to the type or even the
existence of a discontinuity, it is good practice to
repeat the entire liquid penetrant test. If the
indication reappears, it is probably due to a small
discontinuity rather than to incomplete cleaning.
Other Variables Affecting
Indication Appearance
The following variables have a marked effect on
the size, brilliance and appearance of liquid
penetrant indications: condition of surface,
temperature of the part or the liquid penetrant,
dwell times, amount of washing, developer,
conditions of examination and previous testing.
Surface Conditions
There are four general ways in which the surface
conditions can interfere with the proper results from
liquid penetrant testing. 1. Surface openings may
be closed. This can occur when lubricants,
polishing compounds, dirt, scale or other
contaminants are forced into
cracks or holes. Or metal can be peened over
surface discontinuities by forging, polishing or
shot blasting.
2. Rough or porous areas may retain liquid
penetrant, producing irrelevant indications. Or
naturally fluorescent materials (such as many
oils and greases) may cause confusing
indications.
3. Deposits on the surface or in openings may
dilute the liquid penetrant reducing its
effectiveness, or such materials may react with
the liquid penetrant, destroying fluorescence or
dye color.
4. Water or moisture within crack discontinuities
can prevent the liquid penetrant from entering
the crack.
Proper cleaning before liquid penetrant testing
will remove any contaminants, leaving surface
openings clear. If it is impossible to adequately
clean the surface, this fact must be taken into
account when weighing the importance of
indications.
Temperature
The viscosity of most liquids increases at low
temperatures and liquid penetrants are no exception.
If a part is quite cold, under 16 °C (60 °F) for
example, the liquid penetrant may become chilled
and thickened when applied, making the dwell time
for very fine discontinuities longer than for parts at
higher temperatures. If a part or liquid penetrant is
too hot, the volatile components of the liquid
penetrant may evaporate, changing the capability
for revealing small discontinuities. Material
temperatures from 10 to 52 °C (50 to 125 °F)
produce optimum results with conventional liquid
penetrants.
Dwell Time and Washing
Fine liquid penetrant indications usually denote
fine discontinuities. However, fine indications may
also be caused by insufficient dwell time. A
diffused indication may mean a generally porous
condition but may also imply incomplete washing.
If excess liquid penetrant is not removed, false
indications are evident. On the other hand, washing
too long and too hard can remove liquid penetrant
from large or shallow discontinuities, resulting in
less intense indications.
29
Developer
The developer makes indications more visible
by:
1. providing a contrasting background,
2. pulling liquid penetrant out of openings by a
blotting action,
3. making the indication easier to read by
enlarging it as the penetrant spreads into the
developer and
4. reducing glare from reflected light during
observations of fluorescent indications.
A thick film of developer may absorb liquid
penetrant, resulting in faint indications or even
masking very fine discontinuities. Most faulty
liquid penetrant processing techniques are because
of loss of indications.
Previous Testing
In judging the presence or absence of liquid
penetrant indications, the inspector must know
whether the parts have been subjected to other test
processes. If so, extreme care must be taken to
clean parts thoroughly before the additional liquid
penetrant testing.
Test processes, such as fabrication, can change
the surface condition. It is not possible to determine
the relative efficiency of various test processes by
subsequent checks of the same part because many
of the materials used in magnetic particle,
fluorescent liquid penetrant and visible dye liquid
penetrant techniques are incompatible.
Discontinuities may remain undetected by liquid
penetrant testing if magnetic particle testing has
been previously used. The residual iron oxide may
fill or bridge the discontinuity. Similarly,
fluorescent liquid penetrant will often fail to show
discontinuities previously found by visible dye
liquid penetrant because the visible dye may
interfere with fluorescence. Subsequent visible dye
liquid penetrant testing may miss discontinuities
indicated by fluorescent liquid penetrant because
the later affects the visible dye color.
Common Causes of Nonrelevant
and False Indications
Nonrelevant indications may be due to
misapplied or improper testing procedures or to
actual discontinuities that do not affect the usability
of a part. False indications, a subcategory of
nonrelevant indications, are best defined as
indications that distract from the quality of the
inspection but do not indicate a discontinuity in a
part. False indications have several causes but are
usually caused by a deficiency in process control.
Poor Process Control
Regardless of the liquid penetrant technique
used, the level of sensitivity can be adversely
affected by poor process control, such as improper
application of liquid penetrant, improper removal
of liquid penetrant, lack of cleanliness in the
inspection area and poor handling of parts being
processed. Any of these can cause false indications
that will interfere with or cause a distraction during
the visual detection and interpretation of
indications.
Improper application can cause pooling of the
liquid penetrant. This produces an uneven coating
of liquid penetrant on the surface of a part and, on
certain types of materials, results in areas of high
background bleedout.
Improper removal can cause overremoval or
underremoval of excess surface liquid penetrant.
Overremoval is indicated by a complete lack of
background or indications; a slight background is
normal. Overremoval will not result in a false
indication but increases the chances of removing a
valid discontinuity indication. Underremoval of
excess liquid penetrant can cause a high
background intensity and decrease the contrast
needed to reveal small indications. In addition, the
remaining liquid penetrant background may mask a
relevant indication. In either case, a part that has
been subject to improper removal of excess surface
liquid penetrant must be cleaned and reprocessed.
Lack of cleanliness in the inspection area is often
a cause of false indications. An inspection area
should be free of all liquid penetrant. Liquid
penetrant on roller assemblies, dryer shelves or
inspection tables should be cleaned up before parts
are processed. Otherwise the penetrant can be
absorbed by the developer and cause nonrelevant
indications.
Proper handling of parts during all phases of the
liquid penetrant process is important. Rubber gloves
should be cleaned between processing steps. Small
parts processed together should not
30
ASNT Level II Study Guide: Liquid Penetrant Testing
rub against each other. Lint from towels or rags will
fluoresce under near ultraviolet light and give the
appearance of a crack. False indications due to
improper handling of parts can be easily prevented.
Part Geometry and Surface
Condition
The geometry of a part or assembly can cause
nonrelevant indications. The indication of an
interface between a turbine blade and a disk can not
only produce a nonrelevant indication, but can also
mask possible small indications if the bleedout from
the interface is excessive. In many cases inspection
procedures will require that an assembly be
completely disassembled before inspection.
Press fittings are a source of nonrelevant
indications caused by part geometry. It is sometimes
impossible to completely disassemble a part that
must be inspected. The bleedout of the liquid
penetrant around press fittings can be considerable
and can mask relevant indications. In these
situations the part must be monitored very closely
during the developer dwell time to properly evaluate
the indications as they form.
Another cause of false and nonrelevant
indications is a rough part surface. Rough weld bead
surfaces and weld spatter make welds very
difficult to inspect, especially with solvent
removable method. The major concern on a weld
bead is masking of relevant indications. As-cast
and as-forged surfaces may also lead to nonrelevant
indications because of surface roughness or other
irregularities. Machined parts may have machining
grooves or marks, or scratches from rough
handling.
Evaluation of Nonrelevant
Indications
One technique that can be used to help identify a
nonrelevant indication is wiping off the indication
with a solvent dampened, lint free, swab or cloth
and reapplying the developer. The original
developer dwell time must be repeated; however,
the bleedout should be monitored to help evaluate
the indication. If there is no bleedout, the original
indication can be considered nonrelevant or false.
This technique may also reveal multiple relevant
indications that had previously merged into one or
had been hidden by excessive bleedout from an
adjacent nonrelevant indication during the
developer dwell.
Recommended reading
Subject
Reference*
appearance of liquid penetrant indications
A
variables affecting indication appearance
A
causes of nonrelevant indications
A
*See Introduction for explanation of references.
Review Questions
1. One disadvantage of liquid penetrant
inspection is that:
5. A penetrant inspection cannot find:
a. penetrant materials may cause drying
and cracking of the skin.
b. large subsurface discontinuities with
openings to the surface will not form
indications.
c. it can only be used with nonferrous
material.
d. the materials are only available in
aerosol spray cans.
Ref B
2. Which of the following is not a physical
property associated with penetrant
materials?
a.
b.
c.
d.
Solvent resistance.
Flash point.
Viscosity.
Chemical inertness.
grit or sand blasting.
machining.
etching.
quenching.
Ref B
water soluble.
water washable.
nonfluorescent.
solvent removable.
Ref B
6. Which of the methods listed below is most
applicable for detecting fine, tight surface
cracks?
a.
b.
c.
d.
Visible dye, water washable.
Visible dye, postemulsifiable.
Fluorescent, water washable.
Fluorescent, postemulsifiable.
Ref B
a.
b.
c.
d.
immersion.
drain.
dwell.
presoak.
Ref B;Ref C
8. Developer assists in the detection of
discontinuities by:
Ref B
4. A standard classification for a type of
developer is:
a.
b.
c.
d.
surface porosity.
surface cracks.
an internal cavity.
a surface forging lap.
7. The term used to describe the total time
that penetrant remains on the workpiece is:
3. The removal of smeared metal by chemical
processes is called:
a.
b.
c.
d.
a.
b.
c.
d.
Ref B
a.
b.
c.
d.
providing a contrasting background.
emulsifying the penetrant bleedout.
providing a clean surface.
providing a dry surface.
Ref B
32
9. Difficulties with removal of a
postemulsifiable penetrant during the rinse
operation can be overcome by:
a. reapplying a coating of emulsifier.
b. using conditioned (soft) water during
the washing operation.
c. cleaning, then completely reprocessing
the part using a longer emulsification
time.
d. increasing the water temperature during
the washing operation.
Ref B;Ref C
10. Excessive removal of penetrant may result
in:
a. undetected discontinuities during
evaluation.
b. an excessive background that inhibits
the evaluation process.
c. the need to apply the developer twice
to obtain significant bleedout.
d. small, tight cracks that are easily
detected on parts with a smooth
surface.
Ref B
11. Which of the following is an advantage of
a fluorescent water washable penetrant
system compared to a fluorescent
postemulsifiable penetrant system?
a. Water washable is superior for testing
critical in service parts.
b. Water washable has fewer processing
steps.
c. Only wet developer may be used with
postemulsifiable penetrants.
d. Water washable penetrants will more
readily detect fine, tight cracks in
weldments.
Ref B
12. Which of the following is not an advantage
of postemulsifiable fluorescent penetrants?
a. High sensitivity level to detect very
fine defects.
b. They are easily removed with water
after proper emulsification dwell time.
c. They are easily removed from sand
castings after proper emulsification
dwell time.
d. They have higher tolerance to
variations in the removal process when
compared to water washable
penetrants.
Ref B
13. When using the visible, solvent removable
process, after the penetrant dwell time,
excess penetrant is removed by:
a. spraying solvent on the part and then
wiping with a clean, dry rag or paper
towel.
b. wiping off excess penetrant with a
clean, dry rag or paper towel,
moistening the part with solvent and
rewiping the part.
c. wiping off excess penetrant with a
clean, dry rag or paper towel,
moistening a clean cloth with solvent
and rewiping the part.
d. wiping off excess penetrant with a
clean, dry rag or paper towel, then
rewiping with a cloth soaked with
solvent.
Ref B
14. When using a fluorescent, postemulsifiable
penetrant, the best emulsification time is:
a. 10 s.
b. 5 s.
c.
2 to 3 s.
d. determined by experimentation
Ref B
33
15. Which type of developer is generally
considered the most sensitive for locating
fine discontinuities?
a.
b.
c.
d.
Solvent suspended.
Water soluble
Water suspended.
Dry powder.
Ref C
16. Which of the following penetrant systems
is the least sensitive?
a.
b.
c.
d.
fluorescent, postemulsifiable
visible, solvent removable.
fluorescent, solvent removable.
fluorescent, water washable.
Ref B
17. One method for applying dry developer to
a localized area of a large part is with:
a.
b.
c.
d.
a brush.
a powder bulb.
an aerosol can.
an immersion tank.
Ref B
18. Prewash and postwash stations are an
advantage when using which of the
following penetrant methods?
a. Visible, lipophilic postemulsifiable.
b. Fluorescent, hydrophilic
postemulsifiable.
c. Visible, water washable.
d. Fluorescent, lipophilic
postemulsifiable.
Ref B
19. The specific gravity of wet developer is
measured with a:
a.
b.
c.
d.
developer gage.
hydrogage.
balance scale.
hydrometer.
Ref C
20. Which of the following describes the
comparator that is used to monitor the
process performance of the penetrant
system?
a. A panel with one half chrome plated
containing five crack centers and the
other half grit blasted.
b. A cracked aluminum block with a
groove in the center.
c. A chrome plated panel with fine cracks
across the face to a depth equal to the
plating thickness.
d. Ceramic coated block with fine cracks
extending around the entire panel.
Ref B
21. Ultraviolet light intensity is measured with:
a.
b.
c.
d.
a digital or analog UV-A meter.
a photographic light meter.
an infrared meter.
a standard white light meter.
Ref B
22. What instrument is used to check
hydrophilic emulsifier concentration?
a.
b.
c.
d.
A hydrometer.
A capillary fill barometer.
A centrifuge tube.
A refractometer.
Ref B
23. The penetrant performance characteristic
known as sensitivity is defined as the:
a. the contrast between an indication and
the background.
b. ability to produce a visible indication
from a small, tight linear discontinuity.
c. volume percentage of penetrant that
remains in a discontinuity after
processing.
d. ability to enter a discontinuity to form
an indication.
Ref B
34
ASNT Level II Study Guide: Liquid Penetrant Testing
24. A group of nearly rounded indications
located in an area that transitions between
thick and thin sections of aluminum
castings is known as:
a.
b.
c.
d.
shrinkage cracks.
gas holes.
laminations.
cracks due to heat treating.
Ref B
25. Processing a part with developer residue
remaining from a previous penetrant
inspection may result in:
a. an enhanced background contrast.
b. a more rapid formation of indications.
c. a greatly reduced formation of
indications.
d. the elimination of a second application
of developer.
Ref B
26. For intermediate dwell times, applying
fresh penetrant 15 min before removal
assists the process by increasing the:
a. rate of evaporation.
b. time required for the removal
operation.
c. rate of penetration.
d. sensitivity of the penetrant.
28. Repeated or cyclic loads below the yield
strength of a material can cause:
a.
b.
c.
d.
service cracking.
fatigue cracking.
intergranular cracking.
thermal cracking.
Ref B
29. Grinding checks or cracks are caused by:
a.
b.
c.
d.
localized overheating.
a slow feed rate.
unequal heating or cooling.
rapid cooling from high temperatures.
Ref B
30. Elongated inclusions found in bar stock are
called:
a.
b.
c.
d.
seams.
laps.
stringers.
contaminants.
Ref B
31. An advantage of the postemulsification
fluorescent penetrant process is that it:
Ref B
27. How does an increase in temperature affect
the viscosity of a penetrant?
a. It becomes more viscous and decreases
in flow rate.
b. It becomes less viscous and decreases
in flow rate.
c. It becomes more viscous and increases
in flow rate.
d. It becomes less viscous and increases
in flow rate.
Ref B
c.
d.
is very good on rough surfaces such as
sand castings.
has fewer operations than other
penetrant processes.
can be used on anodized surfaces.
can be used to detect wide, shallow
discontinuities.
Ref B;Ref C
32. What comparison standard has control over
the depth and quantity of cracks?
a.
b.
c.
d.
A stainless steel test panel.
A cracked aluminum test block.
A ceramic test block.
A grit blast panel.
Ref B
Review Questions
33. Compared to a certified Level I inspector,
a Level II inspector:
a. can process all forms of a product.
b. is authorized to approve all penetrant
procedures.
c. requires more formal training hours
and work experience.
d. can determine the acceptance criteria
for a part.
Ref B
34. A limitation on materials used to inspect
nickel alloy welds in a nuclear or pressure
vessel system is that the penetrant
materials should have:
a.
sulfur and halogen residual of 10% or
less by weight.
b. sulfur, chlorine and fluorine residual of
1 % or less by weight.
c. chlorine and halogen residual of 5% or
less by weight.
d. halogen and fluoride residual of 10%
or less by weight.
Ref B
35
37. Which of the following would not be the
cause of a nonrelevant indication?
a.
b.
c.
d.
Penetrant on the inspection table.
An improperly cleaned surface.
A corrosion crack.
Penetrant trapped in the threads of a
part.
Ref C
38. The periodic checks performed to assure
that the penetrant testing system is
functioning are called:
a.
b.
c.
d.
process control tests.
maintenance tests.
certification tests.
performance evaluations.
Ref C
39. A relevant indication in a casting may be
caused by:
a.
b.
c.
d.
a burst.
a crater crack.
laminations.
porosity.
Ref C
35. A weld discontinuity that appears
starshaped with small indications
40. The relative size of a surface discontinuity
emanating from a central point is a:
is estimated based on the indication
a. burst.
intensity and the:
b grinding crack.
c. crater crack.
a. amount of bleedout.
d heat affected zone (HAZ) crack.
b. size and shape.
Ref B
c. direction of
bleedout
Ref C
36. Multiple round or nearly round indications
scattered on a weld are the result of:
41. Which of the following is a nonrelevant
indication found during penetrant
a. crater pits.
inspection?
b. undercut.
c. porosity.
a. Marks on the part due to penetrant on
d. weld laps.
Ref B
the inspector's hands.
b. A press fit insert ring in the bore of a
shaft.
c. Linear indications on a heat treated
weldment.
d. Dry developer residue.
Ref B
36
ASNT Level II Study Guide: Liquid Penetrant Testing
42. A visual method used as acceptance
criteria for a part uses:
a.
b.
c.
d.
sized wires.
a calibrated scale.
a testing and monitoring panel.
referenced photographs.
46. Ultraviolet lights over a fluorescent
penetrant wash station are used to:
Ref C
43. The purpose of a penetrant system monitor
is to provide:
a. a method of estimating the cost of
inspection.
b. verification of the overall processing
system performance.
c. standardization for performing process
controls.
d. the means to reject test objects.
Ref B
44. Using a weld standard for interpretation of
indications provides:
a. reliable acceptance criteria.
b. an accurate method to determine repair
costs.
c. the format for a test report.
d. the means to reject linear indications.
Ref B; Ref C
45. Dry developer is checked for fluorescent
contamination by:
a. comparing the in-use developer to new
material.
b. processing a testing and monitoring
panel.
c. a laboratory examination for chemical
composition.
d. viewing under an ultraviolet light for
fluorescent specks.
Ref B
a. verify a uniform coating of penetrant
has been applied to the part.
b. verify the emulsifier covers the entire
surface.
c. monitor the removal of surface
penetrant.
d. check the cleanliness of parts before
processing.
Ref C
47. An advantage of inspecting forgings with
the penetrant process is that:
a. it can detect any type of discontinuity
associated with forgings.
b. there are no limitations to the part size
or shape.
c. forging scale does not interfere with
the test.
d. penetrant materials do not have any
adverse affects on any alloy that is
forged.
Ref B
48. Discontinuities that may be found in
aluminum extrusions are:
a.
b.
c.
d.
porosity and inclusions.
laminations.
cracks.
laps and seams.
Ref B
49. Which of the following discontinuities are
associated with forgings?
a.
b.
c.
d.
Tears.
Cracks.
Bursts.
Blow holes.
Ref B
37
Review Question
Answers
1.
2.
3.
4.
5.
6.
7.
.8.
9.
10.
11.
12.
13.
a
a
c
a
c
d
c
a
c
a
b
c
c
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
d
a
b
b
b
d
a
a
d
b
a
c
c
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
d
b
a
c
d
a
c
b
c
c
c
a
d
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
a
b
d
b
a
d
c
b
d
c
38
ASNT Level II Study Guide: Liquid Penetrant Testing
Appendix Standard
Terminology for the Liquid
Penetrant Examination
This standard terminology is adapted from ASTM E 1316-94.
Angstrom unit - A unit of length that may be used to express the wavelength of electromagnetic
radiation, that is light. One angstrom unit is equal to 0.1 nanometers.
Background -~ The surface of the test part against which the indication is viewed. It may be the
natural surface of the test part or the developer coating on the surface.
Ultraviolet light - Electromagnetic radiation used for nondestructive testing in the range of
wavelength 330 to 390 nm (3300 to 3900 A), also known as UV-A.
Ultraviolet light filter - A filter that transmits near-ultraviolet radiation while absorbing other
wavelengths.
Bieedout - The action of an entrapped liquid penetrant in surfacing from discontinuities to form
indications.
Blotting - The action of the developer in soaking up the penetrant from the discontinuity to
accelerate bieedout.
Carrier - A liquid, either aqueous or nonaqueous, in which liquid penetrant examination
materials are dissolved or suspended.
Clean - Free of contaminants.
Contaminant ~ Any foreign substance present on the test surface or in the inspection materials
that will adversely affect the performance of liquid penetrant materials.
Contrast - The difference in visibility (brightness or coloration) between an indication and the
background.
Defect - One or more flaws whose aggregate size, shape, orientation, location, or properties do
not meet specified acceptance criteria and are rejectable.
Developer - A material that is applied to the test surface to accelerate bieedout and to enhance
the contrast of indications.
Developer, aqueous - A suspension of developer particles in water.
Developer, dry powder - A fine, freeflowing powder used as supplied.
Developer, liquid film - A suspension of developer particles in a vehicle that leaves a
resin/polymer film on the test surface after drying.
Developer, nonaqueous - Developer particles suspended in a nonaqueous vehicle before
application.
40
ASNT Level II Study Guide: Liquid Penetrant Testing
Developer, soluble - A developer completely soluble in its carrier, not a suspension of powder in a
liquid, which dries to an absorptive coating.
Developing time - The elapsed time between the application of the developer and the
examination of the part.
Discontinuity - A lack of continuity or cohesion; an intentional or unintentional interruption in the
physical structure or configuration of a material or component.
Dragout - The carryout or loss of penetrant materials as a result of their adherence to the test
piece.
Drain time - That portion of the dwell time during which the excess penetrant or emulsifier
drains from the part.
Drying oven - An oven used for increasing the evaporation rate of rinse water or an aqueous
developer vehicle from test parts.
Drying time - The time required for a cleaned, rinsed, or wet developed part to dry.
Dwell time - The total time that the penetrant of emulsifier is in contact with the test surface,
including the time required for application and the drain time.
Electrostatic spraying - A technique for attaining a uniform coating in which the material
sprayed is given an electrical charge.
Emulsification time - The time that an emulsifier is permitted to remain on the part to combine
with the surface penetrant before removal. Also called emulsification dwell time.
Emulsifier - A liquid that interacts with an oily substance to make it water washable.
Emulsifier, hydrophilic - A waterbased liquid used in penetrant examination that interacts with
the penetrant oil rendering it water washable. The hydrophilic is supplied in a concentrate
and is mixed with water to a concentration not exceeding that listed in the QPL.
Emulsifier, lipophilic - An oil based liquid used in penetrant examination that interacts with the
penetrant oil rendering it water washable.
Etching - The removal of surface material by chemical or electrochemical methods.
Evaluation - A review, following interpretation of the indications noted, to determine whether they
meet specified acceptance criteria.
False indication - A nondestructive testing indication that is interpreted to be caused by a
discontinuity at a location where no discontinuity exists.
Family - A complete series of penetrant materials required for the performance of a liquid
penetrant examination. The term Family only applies to Method B and Method D and
only includes the penetrant and the emulsifier. Developers are not part of the Family.
Flaw - An imperfection or discontinuity that may be detectable by nondestructive testing and is
not necessarily rejectable.
Flaw characterization - The process of quantifying the size, shape, orientation, location, growth,
or other properties of a flaw based on nondestructive testing response.
Appendix 1, Standard Terminology for the Liquid Penetrant Examination
41
Fluorescence - The emission of visible radiation by a substance as a result of and only during the
absorption of ultraviolet light radiation.
Footcandle - The illumination on a surface, 1 ft2 in area, on which is uniformly distributed a flux of
1 lm (lumen). It equals 10.8 lm/m2.
Immersion rinse - A means of removing surface penetrant in which the test part is immersed in a
tank of either water or remover.
Imperfection -A departure of a quality characteristic from its intended condition.
Indication - Evidence of a discontinuity that requires interpretation to determine its significance.
Inspection - Visual examination of the test part after completion of the liquid penetrant
processing steps.
Interpretation - The determination of whether indications are relevant or nonrelevant.
Liquid penetrant examination - A nondestructive test that uses suitable liquids that penetrate
discontinuities open to the surface of solid materials and, after appropriate treatment,
indicate the presence of discontinuities.
Nondestructive testing (NDT) - The development and application of technical methods to examine
materials or components in ways that do not impair future usefulness and serviceability in
order to detect, locate, measure and evaluate discontinuities, defects and other
imperfections; to access integrity, properties and composition, and to measure geometrical
characteristics.
Nonrelevant indication -A nondestructive testing indication that is caused by a condition or
type of discontinuity that is not rejectable. False indications are nonrelevant.
Over emulsification - Excessive emulsifier dwell time that results in the removal of penetrants
from some discontinuities.
Over washing - Too long or too vigorous washing, or both, which results in removal of
penetrants from some discontinuities.
Penetrant - A liquid which has been formulated to enter surface discontinuites and which
contains a tracer dye.
Penetrant comparator - An intentionally flawed specimen having separate but adjacent areas for
the application of different liquid penetrant materials so that a direct comparison of their
relative effectiveness can be obtained. It can also be used to evaluate liquid penetrant
techniques, liquid penetrant systems, or test conditions.
Penetrant, fluorescent - A penetrant that emits visible radiation when excited by an ultraviolet
light.
Penetrant, postemulsifiable - A liquid penetrant that requires the application of a separate
emulsifier to render the excess surface penetrant water washable.
Penetrant, solvent removable - A liquid penetrant so formulated that most of the excess surface
penetrant can be removed by wiping with lintfree material, with the remaining surface
penetrant traces removable by further wiping with a lintfree material lightly moistened with
solvent remover.
42
ASNT Level II Study Guide: Liquid Penetrant Testing
Penetrant, visible - A liquid penetrant that is characterized by an intense color, usually red.
Penetrant, water washable - A liquid penetrant with a built-in emulsifier.
Pooling - The existence of excessive amounts of penetrant, emulsifier, or developer in an
incompletely drained area.
Post cleaning - The removal of residual liquid penetrant examination materials from the test part
after the penetrant examination has been completed.
Post emulsification - A penetrant removal technique employing a separate emulsifier.
Precleaning - The removal of surface contaminants from the test part so that they will not
interfere with the examination process.
Relevant indication - A nondestructive testing indication that is caused be a condition or type of
discontinuity that requires evaluation.
Rinse - The process of removing liquid penetrant examination materials from the surface of a
test part by means of washing or flooding with another liquid, usually water. The process is
also termed wash.
Solvent remover - A volatile liquid penetrant used to remove excess from the surface being
examined.
Temperature envelope - The temperature range over which a particular penetrant inspection test
will operate.
Viscosity - The property of a fluid that presents a resistance to shearing flow.
Visible light - Electromagnetic radiation in the 400 to 700 nm wavelength range.
Visual adaptation - The adjustment of the eyes when one passes from a bright to a darkened
place.
Water tolerance - The amount of water that a penetrant or emulsifier can absorb before its
effectiveness is impaired.
Wetting action - The ability of a liquid to spread over and adhere to solid surfaces.