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