9.Liquid Penetrant Inspection PT

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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

&ethod

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 &ethod

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.



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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.



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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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• -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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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

9.Liquid Penetrant Inspection PT

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