Liquid Penetrant Inspection

Liquid Penetrant Inspection

• Surface inspection methodSurface inspection method• Applicable to all non-porous, Applicable to all non-porous,

non-absorbing materialsnon-absorbing materials

Dye Penetrant Inspection(DPI)Dye Penetrant Inspection(DPI) Penetrant Flaw Detection (PFD)Penetrant Flaw Detection (PFD) Penetrant Testing (PT)Penetrant Testing (PT)

6 Steps in Penetrant flaw detection

• Surface preparationSurface preparation• Penetrant applicationPenetrant application• Removal of excess penetrantRemoval of excess penetrant• Application of developerApplication of developer• InspectionInspection• Post cleaning and protection Post cleaning and protection

1. Surface Preparation• Physical Methods Physical Methods • Chemical MethodsChemical Methods

• ScaleScale• SlagSlag• Corrosion productsCorrosion products

• Oils and GreasesOils and Greases• PaintsPaints

Chemical Methods• Vapour DegreasingVapour Degreasing• Hot Solvent DegreasingHot Solvent Degreasing• Cold solvent DegreasingCold solvent Degreasing• Solvent materials with EmulsifiersSolvent materials with Emulsifiers• Acid / Alkaline Cleaning Acid / Alkaline Cleaning • Steam cleaningSteam cleaning• Paint RemovalPaint Removal

2. Penetrant Application

• Penetrating fluid applied to component and Penetrating fluid applied to component and drawn into defect by capillary actiondrawn into defect by capillary action

Penetrant Application

Critical factorsCritical factors

• Penetration / Dwell timePenetration / Dwell time

• Component TemperatureComponent Temperature

Principle : Capillary Action• Interaction of adhesive and cohesive Interaction of adhesive and cohesive

forcesforces

Principle : Capillary Action• Interaction of adhesive and cohesive Interaction of adhesive and cohesive

forcesforces

Penetrant Properties• Good Wetting AbilityGood Wetting Ability• High Surface TensionHigh Surface Tension• ViscosityViscosity

Wetting Ability

• Liquids having good wetting ability have Liquids having good wetting ability have a low contact angle.a low contact angle.

• Liquids having a contact angle of 90º or Liquids having a contact angle of 90º or less will act as penetrants.less will act as penetrants.

• Contact angle is strongly affected by Contact angle is strongly affected by surface cleanliness.surface cleanliness.

Contact Contact AngleAngle

Contact AngleContact Angle

LOWLOW HIGHHIGH

Contact AngleContact Angle

Surface Tension

HIGHHIGH LOWLOW

Surface Tension

• Strongly affected by Strongly affected by contaminationcontamination

Viscosity• Viscosity is a measure of internal frictionViscosity is a measure of internal friction• It affects the rate at which a liquid flowsIt affects the rate at which a liquid flows• Viscosity has a strong effect on the time Viscosity has a strong effect on the time

taken for capillary action to worktaken for capillary action to work• A high viscosity penetrant will require a A high viscosity penetrant will require a

longer contact time and a longer longer contact time and a longer development timedevelopment time

• A low viscosity penetrant may drain too A low viscosity penetrant may drain too quickly from vertical or overhead surfaces quickly from vertical or overhead surfaces

Types of Penetrant

• Colour ContrastColour Contrast• FluorescentFluorescent• All other factors being equal, fluorescent All other factors being equal, fluorescent

penetrants provide the best sensitivitypenetrants provide the best sensitivity• Each of the above may be water Each of the above may be water

washable, solvent removable or post-washable, solvent removable or post-emulsifiable (in order of increasing emulsifiable (in order of increasing sensitivity)sensitivity)

2. Penetrant Application

MethodMethodss

SprayingSpraying

BrushingBrushingImmersionImmersion

Preceded by a visual Preceded by a visual inspectioninspection

Penetrant application

• Special MethodsSpecial Methods

Thixotropic Thixotropic penetrantspenetrants

Electrostatic Electrostatic sprayingspraying

3. Removal of Excess Penetrant

• Penetrating fluid applied to component and Penetrating fluid applied to component and drawn into defect by capillary drawn into defect by capillary actionaction• Penetrating fluid removed from component Penetrating fluid removed from component surface (but not from defect)surface (but not from defect)

Removal of Excess Penetrant

• Water washableWater washable• Solvent RemovableSolvent Removable• Post EmulsifiablePost Emulsifiable

Penetrants are formulated for Penetrants are formulated for removal by one or sometimes removal by one or sometimes more than one of the above.more than one of the above.

Removal of Excess Penetrant• Water Washable PenetrantWater Washable Penetrant

Spray Spray washwash

Minimise mechanical Minimise mechanical actionactionPressure as low Pressure as low as possibleas possibleTemperature less Temperature less than 50ºCthan 50ºC

Water Washable PenetrantADVANTAGESADVANTAGES• Usable on rough Usable on rough

surfacessurfaces• Suitable for batch Suitable for batch

testingtesting• Cheaper than Cheaper than

other methodsother methods

DISADVANTAGESDISADVANTAGES• Susceptible to Susceptible to

over washingover washing• Least sensitive Least sensitive

methodmethod• Requirement for a Requirement for a

water sourcewater source

Post Emulsifiable Post Emulsifiable Penetrant Penetrant StagesStages

• Immerse component in penetrantImmerse component in penetrant• Immerse component in emulsifierImmerse component in emulsifier• Emulsifier diffuses into the Emulsifier diffuses into the penetrant making it water penetrant making it water washablewashable• Water wash removes excess Water wash removes excess penetrant penetrant / emulsifier / emulsifier • Penetrant in defects left Penetrant in defects left unaffectedunaffected

Removal of Excess Penetrant

2 Post emulsification 2 Post emulsification systemssystems

HydrophilicHydrophilic

LipophilicLipophilicContact time criticalContact time criticalDetermined by experimentationDetermined by experimentation

Post emulsifiableADVANTAGESADVANTAGES• Maximum Maximum

penetrating abilitypenetrating ability• Greater control Greater control

over penetrant over penetrant removalremoval

DISADVANTAGESDISADVANTAGES• Not suited to Not suited to

rough surfacesrough surfaces• More expensiveMore expensive• More time More time

consumingconsuming

Removal of Excess Penetrant

Clean off the excess with a lint free Clean off the excess with a lint free cloth.cloth.

Wipe with a solvent dampened rag.Wipe with a solvent dampened rag.

Solvent Solvent RemovableRemovable

Thou shalt not spray the cleaner directly onto the item under test.

Solvent Removable ADVANTAGESADVANTAGES• PortabilityPortability• No water supply No water supply

neededneeded

DISADVANTAGESDISADVANTAGES• Not suited to batch Not suited to batch

testingtesting• Requires hand wiping so Requires hand wiping so

time consumingtime consuming• More expensive than More expensive than

water washablewater washable• Potentially hazardous Potentially hazardous

chemicalschemicals

Drying

Hot air recirculating oven (max 80ºC)Hot air recirculating oven (max 80ºC)

Forced warm airForced warm air

Dry clean compressed airDry clean compressed air

Component temperature shall not Component temperature shall not exceed 50ºCexceed 50ºC

4. Development• Penetrating fluid applied to component and Penetrating fluid applied to component and drawn into defect by capillary drawn into defect by capillary actionaction• Developer applied to surface Developer applied to surface

Developer Properties

• AbsorptiveAbsorptive• Fine textureFine texture• Able to mask out Able to mask out

background colourbackground colour• Evenly and easily Evenly and easily

applicableapplicable• Light and even coatLight and even coat• Non-fluorescingNon-fluorescing

Easily wettedEasily wettedContrasting colourContrasting colourEasily removedEasily removedNon-toxic and Non-Non-toxic and Non-irritantirritant

Developer action• Penetrating fluid applied to component and Penetrating fluid applied to component and drawn into defect by capillary drawn into defect by capillary actionaction• Developer applied to surface Developer applied to surface • Penetrant drawn back out of the defect by Penetrant drawn back out of the defect by reverse capillary action reverse capillary action

Developer actionDeveloper actionCapillary Action - Increases the size of an Capillary Action - Increases the size of an indication far beyond the actual defect size; indication far beyond the actual defect size; increases the “thickness” of an indication, increases the “thickness” of an indication, thereby increasing it’s colour brilliance.thereby increasing it’s colour brilliance.Light scattering - Aids the conversion of UVA to Light scattering - Aids the conversion of UVA to visible light when using fluorescent systems; visible light when using fluorescent systems; reduces background glare when using visible reduces background glare when using visible systems.systems.Solvent Action - Solvent combines with Solvent Action - Solvent combines with penetrant, reducing penetrant viscosity, thereby penetrant, reducing penetrant viscosity, thereby inducing a more rapid, more efficient bleed-out.inducing a more rapid, more efficient bleed-out.

Light ScatteringI0 IfIfIf

If

No Developer With Developer

No Developer With Developer

DevelopmentDry powderDry powder Component must be Component must be drydryApplied by Applied by Dipping Dipping BlowingBlowingDust storm cabinet Dust storm cabinet

Aqueous liquidAqueous liquid Dry after applicationDry after applicationApplied by Applied by Immersion Immersion SprayingSprayingBrushing Brushing

Non-Aqueous liquidNon-Aqueous liquid Applied by Applied by Aerosol Aerosol

Dry powder developerADVANTAGESADVANTAGES• Easy to handleEasy to handle• No hazardous No hazardous

vapoursvapours• Easy to removeEasy to remove

DISADVANTAGESDISADVANTAGES• Difficult to see if Difficult to see if

properly appliedproperly applied• Fine powders can be Fine powders can be

hazardoushazardous• Does not offer the Does not offer the

best degree of colour best degree of colour contrast contrast

Aqueous Developer

• SolutionsSolutions

Aqueous Developer

• SolutionsSolutions • SuspensionsSuspensions

Aqueous DeveloperADVANTAGESADVANTAGES• No vapours or dustNo vapours or dust• Cheaper than non-Cheaper than non-

aqueous aqueous

DISADVANTAGESDISADVANTAGES• Difficult to apply Difficult to apply

evenlyevenly• Requires drying Requires drying

after applicationafter application

Non-Aqueous DeveloperADVANTAGESADVANTAGES• Most sensitiveMost sensitive• Usable with Usable with

fluorescent or fluorescent or colour contrastcolour contrast

DISADVANTAGESDISADVANTAGES• Hazardous Hazardous

solventssolvents• Higher costHigher cost• Need to be Need to be

correctly appliedcorrectly applied

Developer Sensitivity • Dry powderDry powder 100 - 140 %100 - 140 %• Aqueous solutionAqueous solution 110 - 150 %110 - 150 %• Aqueous suspensionAqueous suspension 120 - 200%120 - 200%• Non-AqueousNon-Aqueous 120 - 240%120 - 240%

System Classification • Type of penetrantType of penetrant• Method of penetrant removalMethod of penetrant removal• Type of developerType of developer

System classification

• PENETRANTPENETRANT• Colour Colour

contrastcontrast• FluorescentFluorescent• Dual Dual

REMOVALREMOVALWater washableWater washableSolventSolventPost Post emulsifiableemulsifiable

DEVELOPERSDEVELOPERSDry powderDry powderAqueousAqueousNon-AqueousNon-Aqueous

5. Inspection• Indications viewed as soon as practicable Indications viewed as soon as practicable

after developer application with final after developer application with final assessment taking place after a minimum assessment taking place after a minimum development time has elapsed.development time has elapsed.

30 Seconds30 Seconds 1 Minute1 Minute 15 Minutes15 Minutes

5. Inspection

Colour ContrastColour Contrast• White light above 500 luxWhite light above 500 lux

FluorescentFluorescent• White light below 20 luxWhite light below 20 lux• UV-A above 1000µW / cmUV-A above 1000µW / cm2 2

Lighting levels criticalLighting levels critical

5. InspectionFluorescentFluorescent• Allow 15 minutes lamp warm-upAllow 15 minutes lamp warm-up•Allow 5 minutes dark adaptationAllow 5 minutes dark adaptation•Do not wear photo-chromatic spectaclesDo not wear photo-chromatic spectacles

6. Post CleaningDPI residues are required to be removed DPI residues are required to be removed

becausebecause• They may be harmful to the componentThey may be harmful to the componentoror• They may impair subsequent processingThey may impair subsequent processing

Advantages of DPI• Applicable to all non-porous materialsApplicable to all non-porous materials• Able to test large parts with a portable kitAble to test large parts with a portable kit• Batch testingBatch testing• Applicable to small parts with complex Applicable to small parts with complex

geometrygeometry• Simple,cheap, easy to interpretSimple,cheap, easy to interpret• Good sensitivityGood sensitivity• Training requirements typically less than Training requirements typically less than

for other NDT methods.for other NDT methods.

Disadvantages of DPI• Will only detect defects open to the Will only detect defects open to the

surfacesurface• Careful surface preparation requiredCareful surface preparation required• Not applicable to porous materialsNot applicable to porous materials• Temperature dependentTemperature dependent• Cannot retest indefinitelyCannot retest indefinitely• Compatibility of chemicalsCompatibility of chemicals

Penetrant SystemsPenetrant Systems

PENETRANT

Colour contrastFluorescent

Dual

REMOVAL

Solvent

Water washable

Post emulsifiable

DEVELOPERS

Dry powder

Aqueous

Non-Aqueous

Selection of System• Nature of discontinuities (size and type)Nature of discontinuities (size and type)• Geometry and intricacyGeometry and intricacy• Surface condition Surface condition • Component material and applicationComponent material and application• Size and positionSize and position• Equipment and expertise availableEquipment and expertise available• CostCost• Number of components to be testedNumber of components to be tested

Control Checks• Tank levelsTank levels• Overall system performanceOverall system performance

Overall System Performance

• Chromium plated cracked test panelChromium plated cracked test panel• Cracked test pieceCracked test piece• Quench cracked aluminium alloy blockQuench cracked aluminium alloy block

Control ChecksControl ChecksTank levelsTank levelsOverall system performanceOverall system performanceRinse water temperatureRinse water temperatureOven temperatureOven temperatureEquipment cleanlinessEquipment cleanlinessAirline filtersAirline filtersUV-A filtersUV-A filters

Control ChecksControl ChecksUV-A / visible light levelsUV-A / visible light levelsFluorescent / colour intensityFluorescent / colour intensitySuppliers checkSuppliers checkHydrophilic remover dilutionHydrophilic remover dilutionDeveloperDeveloperMeter / gauge calibrationsMeter / gauge calibrations

Control Checks - Control Checks - FrequencyFrequency

Tank levels Tank levels Overall system performanceOverall system performanceRinse water temperatureRinse water temperatureOven temperatureOven temperatureEquipment cleanlinessEquipment cleanlinessAirline filtersAirline filtersUV-A filtersUV-A filtersUV-A / visible light levelsUV-A / visible light levels

DailyDailyDailyDailyDailyDailyDailyDailyDailyDailyWeeklyWeeklyDailyDailyMonthlyMonthly

Control Checks - Control Checks - FrequencyFrequency

Fluorescent / colour intensityFluorescent / colour intensitySuppliers checkSuppliers checkHydrophilic remover dilutionHydrophilic remover dilutionDeveloperDeveloperMeter / gauge calibrations Meter / gauge calibrations

MonthlyMonthlyAnnual Annual when freshwhen freshDailyDailyAnnualAnnual

UV(A)

Electromagnetic Spectrum

1010-10 -10 1010-8 -8 1010-6 -6 1010-4 -4 1010-2 -2 1cm 101cm 102 2 10104 4 10106 6

10108 8 WavelengthWavelength

Electric Electric WavesWaves

TVTV

MicrowavesMicrowavesInfra redInfra redUltra Ultra

violetviolet

X-rays & X-rays & GammaGamma

LightLight

10 100 200 300 400 500 600 70010 100 200 300 400 500 600 700 ULTRAVIOLET VISIBLEULTRAVIOLET VISIBLE

LIGHTLIGHT LIGHT LIGHT

A Damaged Black Light Emits

UV-AUV-AUV-BUV-BUV-CUV-C

Electromagnetic Spectrum

Fluorescence UV-A SourceUV-A Source :: Mercury vapour arc Mercury vapour arc

lamplamp ++FilterFilter

PrecautionsPrecautions• Avoid looking directly at the lamp Avoid looking directly at the lamp • Do not use if filter is cracked, damaged or Do not use if filter is cracked, damaged or incorrectly fitted incorrectly fitted

Fluorescence and the Electromagnetic Spectrum

10 100 200 300 400 500 600 70010 100 200 300 400 500 600 700 ULTRAVIOLET VISIBLEULTRAVIOLET VISIBLE

LIGHTLIGHT LIGHT LIGHT

EmitsEmits DualDualAbsorbsAbsorbs

Fluorescent v Colour Contrast• Fluorescent more sensitiveFluorescent more sensitive• Less operator fatigue with fluorescentLess operator fatigue with fluorescent• More difficulty in monitoring fluorescent More difficulty in monitoring fluorescent

penetrant removalpenetrant removal• Fluorescence may degrade under UV(A), Fluorescence may degrade under UV(A),

when exposed to acid and high when exposed to acid and high temperaturestemperatures