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PENETRANT TESTING
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Introduction
• This module is intended to provide anintroduction to the NDT method of penetranttesting.
• Penetrant Testing, or PT, is a nondestructive
testing method that uilds on the principleof !isual Inspection.
• PT increases the"seeailit#$ of smalldiscontinuities thatthe human e#e mightnot e ale to detectalone.
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%utline
• General Introduction• Penetrant &aterials and 'onsiderations• (asic Steps in Penetrant Testing
• 'ommon E)uipment• Advantages and *imitations• Summar#
• Glossar# of Terms
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+o Does PT -or/
• In penetrant testing, a li)uid ith high surfaceetting characteristics is applied to the surface ofa component under test.
• The penetrant "penetrates$ into surface reaingdiscontinuities via capillar# action and other
mechanisms.• E0cess penetrant is removed from the surface and
a developer is applied topull trapped penetrant acthe surface.
• -ith good inspectiontechni)ue, visualindications of an#discontinuities present
ecome apparent.
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-hat &aes PT -or/
• Ever# step of the penetrantprocess is done to promotecapillar# action.
• This is the phenomenon of ali)uid rising or climing hen
confined to small openings dueto surface etting properties ofthe li)uid.
• Some e0amples1− Plants and trees dra ater up from
the ground to their ranches andleaves to suppl# their nourishment.
− The human od# has miles ofcapillaries that carr# life sustaininglood to our entire od#.
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(asic Process of PT
23 'lean 4 Dr# 'omponent 53 Appl# Developer 63 Appl# Penetrant
73 Remove E0cess83 !isual Inspection
93 Post 'lean 'omponent
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-hat 'an (e Inspected !ia PT/
Almost an#
material that
has a relativel#
smooth, non:porous surface
on hich
discontinuities
or defects aresuspected.
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-hat 'an NOT e Inspected !ia PT/
•'omponents ith roughsurfaces, such as sandcastings, that trap and holdpenetrant.
•Porous ceramics
•-ood and other firousmaterials.•Plastic parts that asor or
react ith the penetrantmaterials.
•'omponents ith coatingsthat prevent penetrants fromentering defects.
Defect indicationsecome less
distinguishale asthe acground"noise$ levelincreases.
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-hat T#pes of Discontinuities
'an (e Detected !ia PT/
All defects that are opento the surface.
– Rolled products:: cracs,
seams, laminations. – 'astings::cold shuts, hot
tears, porosit#, lo holes,shrinage.
– ;orgings< cracs, laps,
e0ternal ursts. – -elds< cracs, porosit#,
undercut, overlap, lac offusion, lac of penetration.
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'hoices of Penetrant &aterials
Penetrant T#peI ;luorescent
II !isile
ðod
A -ater -ashale( Postemulsifiale : *ipophilic
' Solvent Removale
D Postemulsifiale : +#drophilic
Developer ;ormDr# Poder -et, -ater Solule
-et, -ater Suspendale
-et, Non:A)ueous
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Penetrant &aterials
Penetrants are formulated to possess a numerof important characteristics. To perform ell, apenetrant must1
−Spread easil# over the surface eing inspected.
−
(e dran into surface reaing defects # capillar#action or other mechanisms.
−Remain in the defect ut remove easil# from thesurface of the part.
−Remain fluid through the dr#ing and developing steps
so it can e dran ac to the surface.−(e highl# visile or fluoresce rightl# to produce eas#
to see indications.
−Not e harmful to the inspector or to the materialeing tested.
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Sensitivit# *evels
• Penetrants are also formulated to produce a variet#of sensitivit# levels. The higher the sensitivit#level, the smaller the defect that the penetrants#stem is capale of detecting.
• The five sensitivit# levels are1−
*evel 5 : =ltra:+igh Sensitivit#
− *evel 7 : +igh Sensitivit#
− *evel 6 : &edium Sensitivit#
− *evel 2 : *o Sensitivit#
• As the sensitivit# level increases, so does thenumer of non relevant indications. Therefore, apenetrant needs to e selected that ill find thedefects of interest ut not produce too man# nonrelevant indications.
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!isile !s ;luorescent PT
• Inspection can e performedusing visile >or red d#e3 orfluorescent penetrantmaterials.
• !isile Pt is performed underhite light hile fluorescentPT must e performed usingan ultraviolet light in adarened area. All are all inthe level 2 sensitivit# range.
• ;luorescent PT is moresensitive than visile PTecause the e#e is moresensitive to a rightindication on a daracground. Sensitivit#ranges from 2 to 5.
Photo Courtesy of Contesco
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Penetrant Removal ðod
Penetrants are also classified # themethod of removing the e0cess penetrant.
•Solvent Removale penetrants are removedby wiping with a cloth dampened with solvent. Theyare supplied in aerosol cans for portability and are
primarily used for spot checks.•-ater -ashale penetrants are removed with a
course spray of water. They are the easiest toemploy and most cost effective when inspectinglarge areas.
•Post:Emulsifiale penetrants are water-washable only after they have reacted with anemulsifier solution. A post-emulsifiable system isused when washing the penetrant out of the defectis a concern. The emulsifier is given time to reactswith the penetrant on the surface but not thepenetrant trapped in the flaw.
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Developers
•The role of the developer is to pull trappedpenetrant out of defects and to spread itout on the surface so that it can e seen.Also provides a light acground toincrease contrast hen visile penetrant is used.
• Developer materials are availale in several different forms−
Dr# Poder is a mix of light fluffy powder that clumps together where penetrantbleeds back to the surface to produces very defined indications.
− -et, -ater Suspendale is a powder that is suspended in a water that coversthe surface with a relatively uniform layer of developer when the water is evaporated.The solution is somewhat difficult to maintain as the powder settles out over time.
− -et, -ater Solule is a crystalline powder that forms a clear solution whenmixed with water. The solution recrystallizes on the surface when the water is driven
off. ndications sometimes lack definition and look milky. !ot recommended for usewith water-washable penetrants.
− -et, Non:A)ueous - is supplied in a spray can and is the most sensitivedeveloper for inspecting small areas. t is too costly and difficult to apply to largeareas.
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9 Steps of Penetrant Testing
2. Pre:'lean
6. Penetrant Application
7. E0cess Penetrant
Removal
5. Developer Application
8. Inspect?Evaluate
9. Post:clean
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Pre:cleaning < Step 2
Pre:cleaning is themost important stepin the PT process@@@
• Parts must e free of dirt,rust, scale, oil, grease, etc.to perform a relialeinspection.
• The cleaning process must
remove contaminants fromthe surfaces of the partand defects, and must notplug an# of the defects.
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'aution Aout &etal SmearingSome machining, surface finishing and cleaning
operations can cause a thin la#er of metal tosmear on the surface and prevent penetrant from
entering an# flas that ma# e present.
Etching of the surface prior to inspection is
sometimes re)uired.
(efore Sanding
After Sanding
After Etching
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Penetrant Application < Step 6
&an# methodsof application
are possile
such as1
– (rushing
– Spra#ing
– Dipping?
Immersing
– ;lo:on
– And more
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Dell Time
•The penetrant solutionmust e alloed to"dell$ on the surface ofthe part to allo thepenetrant time to fill an#defects present.
•The dell time var#according to penetrantt#pe, temperature,
material t#pe and surfacefinish.
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E0cess Penetrant Removal < Step 7
The removal techni)ue depends upon
the t#pe of penetrant used, as stated
earlier
– Solvent Removale
– -ater -ashale
– Post Emulsifiale
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E0cess Penetrant Removal < Step 7 >cont.3
-ater -ashale• A coarse ater spra# is
used to remove thee0cess penetrant.
• The procedure used asa guideline for theinspection ill specif#ater temperature
>t#picall# 8B:2BBC;3 andpressure >t#picall# notmore than 5B psi3, etc.
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Solvent Removale•The part is iped ith
a clean dr# cloth toremove the ul of the
e0cess penetrant.•Then, a cloth lightl#
dampened ith solventis used to remove an#
remaining penetrant onthe surface.
E0cess Penetrant Removal < Step 7 >cont.3
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Solvent Removale >cont.3
An# time a solvent isused in the penetrant
inspection process, asuitale flash time isre)uired to allo e0cesssolvent to evaporate.
E0cess Penetrant Removal < Step 7 >cont.3
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E0cess Penetrant Removal < Step 7 >cont.3Post Emulsifiale
• -hen there is concern aout removing much of thepenetrant from the defect, a post emulsifiale s#stem isused.
• This involves an additional stepin hich an emulsifier is applied
to the surface of the part afterthe penetrant dell time.
• The emulsifier is given ustenough time to react iththe penetrant on the surface
to render it ater ashaleut not enough time to diffuseinto the penetrant trapped inthe defects.
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Developer Application < Step 5
The method of developer application is isdependent on the t#pe of developer used.The primar# methods for the folloing maindeveloper t#pes ill e covered in the
folloing slides. – Dr#
– -et
– Nona)ueous -et
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Developer Application < Step 5 >cont.3
Dr# Poder Developer • Prior to appl#ing a dr#
poder developer, thecomponent must ethoroughl# dried. Dr#ing
is usuall# accomplishedin a hot air circulatingoven.
• The developer is thenapplied # immersing the
part in the poder or #dusting of the part iththe poder.
• The part can also eplaced in a developer dust
cloud chamer.
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Developer Application < Step 5 >cont.3
• -et developers are applied #immersing or spra#ing thepart hile it is still et from
the penetrant removalprocess.
• The part is completel# coatedand the e0cess li)uid alloedto drain to prevent pooling
• The part is then dried in a hotair circulating oven.
-et Developer >ater: suspendedand ater: solule3
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Developer Application < Step 5 >cont.3
Nona)ueous Developer >AASolvent:Suspended3
• Nona)ueous developer isapplied # a aerosol spra#to a thoroughl# dried and
cooled part.• A thin even coating shoulde applied. The coatingshould e hite ut stillslightl# transparent hen
performing a visile d#epenetrant inspection, andeven thinner henperforming a fluorescentpenetrant inspection.
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Inspection?Evaluation < Step 8
In this step theinspector evaluates thepenetrant indicationsagainst specifiedaccept?reect criteria
and attempts todetermine the origin ofthe indication.
The indications are
udged to e eitherrelevant, non:relevant orfalse.
Non:relevant eld geometr# indications
Relevant crac indications from an
ausive drilling process
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Inspection?Evaluation < Step 8
A ver# importantstep of evaluation isto document findingson an inspectionreport form or other
record eeping form.This ma# esupported ithdraings or photos
of indications, etc.
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Post 'lean < Step 9
The final step in thepenetrant inspectionprocess is to thoroughl#clean the part that haseen tested to remove allpenetrant processing
materials.
The residual materialscould possil# affect theperformance of the part oraffect its visual appeal.
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Penetrant Inspection S#stems
Penetrant s#stems can e highl# portale orstationar#.
"ortable "enetrant #ystem #tationary "enetrant #ystem
mage courtesy of !ebraska Army !ational $uard
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!erification of Penetrant
S#stem PerformanceSince penetrant testing
involves multiple
processing steps, the
performance of the
materials and theprocesses should e
routinel# checed using
performance verification
tools, hich include1− TA& Panels
− 'rac Sensitivit# Panels
− Run 'hec Panels
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Advantages of Penetrant Testing
•Relative ease of use.
• 'an e used on a ide range of material t#pes.• *arge areas or large volumes of parts?materials can e
inspected rapidl# and at lo cost.
• Parts ith comple0 geometries are routinel#inspected.• Indications are produced directl# on surface of the
part providing a visual image of the discontinuit#.
• Initial e)uipment investment is lo.• Aerosol spra# cans can mae e)uipment ver#
portale.
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*imitations of Penetrant Testing
• %nl# detects surface reaing defects.• Re)uires relativel# smooth nonporous material.• Precleaning is critical. 'ontaminants can mas
defects.
• Re)uires multiple operations under controlledconditions.• 'hemical handling precautions necessar# >to0icit#,
fire, aste3.
• &etal smearing from machining, grinding and otheroperations inhiits detection. &aterials ma# needto e etched prior to inspection.
• Post cleaning is necessar# to remove chemicals.
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Summar#
• Penetrant testing >PT3 is one of the mostidel# used nondestructive testingmethods.
• Its popularit# can e attriuted to tomain factors, hich are its relative ease ofuse and its fle0iilit#.
• +oever, PT involves a numer of
processing steps that must e closel#control to achieve optimal sensitivit#.
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Glossar# of Terms
• 'apillar# Action - the tendency of certainli%uids to travel or climb when exposed tosmall openings.
• 'ontrast - the relative amount of light emittedor reflected between and indication and itsbackground.
• Defect - a discontinuity that effects theusefulness of a part or specimen.
• Developer - a finely divided material appliedover the surface of a part to help promotereverse capillary action and thus bring out apenetrant indication.
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Glossar# of Terms
• Discontinuit# - any interruption in the normalphysical structure of a part or weld. t may ormay not affect the usefulness of a part.
• Dell Time - the period of time that apenetrant or developer must remain in contactwith the surface of a part under test.
• Emulsification Time - the time allowed for theemulsifier to give the penetrant water washableand thus allow the part to be washed.
• Emulsifier - a material applied over a film ofpenetrant that give it water-washable.
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Glossar# of Terms
• Evaluation - the process of deciding as to theseverity of the condition after an indication hasbeen interpreted.
• ;alse Indication - an indication caused by
improper processing& not caused by a relevant ornon-relevant condition.
• ;lash Time - the time re%uired for the solvent toevaporate from the surface of a part when usedto preclean or remove excess penetrant.
• ;luorescent D#e - a dye which becomesfluorescent 'gives off light( when exposed toshort wave radiation such as ultraviolet light.
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Glossar# of Terms
• Indication - the visible evidence or penetrantbleed-out on the surface of the specimen• Interpretation - the process of evaluating an
indication in an attempt to determine the cause
and nature of the discontinuity.• Non:A)ueous Developer - a developer in
which developing powder is applied as asuspension in a %uick drying solvent
• Penetrant - a li%uid used in fluorescent orvisible dye penetrant inspection to penetrateinto the surface openings of parts inspected viathese methods
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Glossar# of Terms
• Relevant Indication - an indication that has beendetermined not to be false or non-relevant - andactual discontinuity
• Seeailit# - the characteristic of an indication thatenables it to be seen against the adverseconditions of background) outside light) etc.
• Sensitivit# - the ability of a penetrant to detectsurface openings. *igher sensitivity indicatessmaller discontinuities can be detected
• =ltraviolet *ight 'or +lack ,ight( - light energy ustbelow the visible range of violet light '/0nanometers(.
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Glossar# of Terms
• !iscosit# - the resistance of a fluid to themotion of its particles• -ashailit# - the property of a penetrant
which permits it to be cleaned from the
surface of a part by washing with water