PENETRANT TESTINGPENETRANT TESTING

NDT METHODNDT METHOD

INTRODUCTIONINTRODUCTION

It draws Penetrant from the flaw to reveal It draws Penetrant from the flaw to reveal its presence. Ability of a liquid to be drawn its presence. Ability of a liquid to be drawn into a “clean” surface breaking flaw by into a “clean” surface breaking flaw by capillary action.capillary action.

After some time “dwell”, excess Penetrant After some time “dwell”, excess Penetrant is removed.is removed.

Developer applied which acts as a Developer applied which acts as a “blotter”. “blotter”.

Visible Penetrants require good white light Visible Penetrants require good white light while fluorescent Penetrants in darkened while fluorescent Penetrants in darkened conditions with an UV “black light”.conditions with an UV “black light”.

IntroductionIntroduction

Precleaning Application of penetrant

Removal of penetrant

Application of developer

Interpretation

PRINCIPLE OF PTPRINCIPLE OF PT

““CapillarityCapillarity

or or Capillary Capillary action”action”

PT indicationPT indication

Advantages & Limitations of Advantages & Limitations of PTPT

1.1. Highly sensitive to small Highly sensitive to small surface flaws.surface flaws.

2.2. Simple in application.Simple in application.

3.3. Large areas & No. of parts Large areas & No. of parts can be inspected rapidly.can be inspected rapidly.

4.4. Complex geometric shapes Complex geometric shapes are routinely inspected.are routinely inspected.

5.5. Visual representation of Visual representation of flaw.flaw.

6.6. Spray cans are very Spray cans are very portable.portable.

7.7. Relatively inexpensive.Relatively inexpensive.

1.1. Only surface breaking Only surface breaking defects can be defects can be detected.detected.

2.2. Only nonporous surface Only nonporous surface can be inspected.can be inspected.

3.3. Pre cleaning is very Pre cleaning is very critical.critical.

4.4. Surface finish & Surface finish & roughness can affect roughness can affect inspection sensitivity.inspection sensitivity.

5.5. Proper disposal of Proper disposal of chemicals is required.chemicals is required.

Basic Steps in PTBasic Steps in PT1.1. PrecleaningPrecleaning

2.2. Application of penetrantApplication of penetrant

3.3. Dwell timeDwell time

4.4. Removal of excess penetrantRemoval of excess penetrant

5.5. Application of developerApplication of developer

6.6. Inspection, evaluation & recordingInspection, evaluation & recording

7.7. Post cleaningPost cleaning

1. PRECLEANING1. PRECLEANING

One of the most One of the most critical steps in PT.critical steps in PT.

The surface must be The surface must be free of oil, grease, free of oil, grease, water, or other water, or other contaminants that contaminants that prevent penetrant prevent penetrant from entering flaws. from entering flaws.

2. 2. APPLICATION OF APPLICATION OF PENETRANTPENETRANT

1.1. SprayingSpraying With low pressure With low pressure

circulation pumps, circulation pumps, or from pressurized or from pressurized spray cans (at 45 spray cans (at 45 deg & 12” from test deg & 12” from test article).article).

APPLICATON OF PENETRANTAPPLICATON OF PENETRANT

2. Brushing2. Brushing

3. 3. PouringPouring

4. Immersing/ 4. Immersing/ DippingDipping

3. 3. DWELL TIMEDWELL TIME

Total time that penetrant is in contact with part Total time that penetrant is in contact with part surface or surface or

Dwell times are recommended by the penetrant Dwell times are recommended by the penetrant producers or required by the specification being producers or required by the specification being followed.followed.

The times vary depending on :The times vary depending on : application, penetrants, material, material form & application, penetrants, material, material form &

type of defect.type of defect. The dwell time never depends on shape & size of the The dwell time never depends on shape & size of the

part.part. Mini. dwell time range from 5 to 60 min.Mini. dwell time range from 5 to 60 min.

4. 4. REMOVAL OF EXCESS REMOVAL OF EXCESS PENETRANTPENETRANT

Depending on the Depending on the penetrant system penetrant system used, used,

1.1. cleaning with a cleaning with a solvent, solvent,

2.2. direct rinsing with direct rinsing with water, water,

3.3. Or first treated with an Or first treated with an emulsifier & then emulsifier & then rinsing with water.rinsing with water.

5. 5. APPLICATION OF DEVELOPERAPPLICATION OF DEVELOPER A thin developer layer A thin developer layer

is applied to the part to is applied to the part to draw penetrant draw penetrant trapped in flaws back trapped in flaws back to surface where it will to surface where it will be visible.be visible.

Applied by dusting (dry Applied by dusting (dry powder), dipping/ powder), dipping/ spraying (wet spraying (wet developers).developers).

Mini. development time Mini. development time is 10 min. is 10 min.

6. INSPECTION, EVALUATION & 6. INSPECTION, EVALUATION & RECORDINGRECORDING

Inspection is performed under Inspection is performed under appropriate lighting to detect indication appropriate lighting to detect indication from flaws.from flaws.

7. POST CLEANING7. POST CLEANING

Thoroughly clean Thoroughly clean the part surface to the part surface to remove developer remove developer from the parts.from the parts.

SURFACE PREPARATION OR SURFACE PREPARATION OR PRECLEANINGPRECLEANING

1. Solvent Cleaners1. Solvent Cleaners

Used to dissolve & Used to dissolve & flush away oils & flush away oils & greases.greases.

Solvents are Solvents are flammable, toxic, flammable, toxic, volatile in nature.volatile in nature.

Ex. Acetone, Ex. Acetone, Isopropyl Alcohol, Isopropyl Alcohol, Petrol, Kerosene, etc.Petrol, Kerosene, etc.

2.2. Detergent Detergent cleaningcleaning

An effective method An effective method for removing oils.for removing oils.

Non-flammable, Non-flammable, water-soluble & water-soluble & corrode the matls. corrode the matls.

Thorough rinsing & Thorough rinsing & drying should follow drying should follow this process.this process.

Pre-cleaningPre-cleaning3.3. Vapor DegreasingVapor Degreasing Used for removing oil & grease.Used for removing oil & grease. Resultant heating helps to drive off moisture. Resultant heating helps to drive off moisture. Chlorinated solvents can harm matls. (nickel, Chlorinated solvents can harm matls. (nickel,

stainless steels & titanium). stainless steels & titanium).

4.4. Mechanical CleaningMechanical Cleaning Used to remove heavy scaling by sand or Used to remove heavy scaling by sand or

grid blasting, grinding, wire brushing use of grid blasting, grinding, wire brushing use of emery papers etc.& emery papers etc.&

followed by an acid or alkali etchfollowed by an acid or alkali etch

Pre-cleaningPre-cleaning5)5) EtchingEtching Used for descaling & rust Used for descaling & rust

removal .removal .

6)6) Paint RemoversPaint Removers Paints can be removed Paints can be removed

effectively with paint effectively with paint removers.removers.

7)7) Steam CleaningSteam Cleaning As it may not reach to As it may not reach to

deep flaws, so deep flaws, so followed by a solvent followed by a solvent

soak.soak. Used for large items to Used for large items to

remove inorganic oils.remove inorganic oils.

8)8) Ultrasonic CleaningUltrasonic Cleaning This is often combined This is often combined

with a solvent or a with a solvent or a detergent bath to detergent bath to improve cleaning improve cleaning efficiency & reduce efficiency & reduce cleaning time.cleaning time.

Characteristics of a Characteristics of a PenetrantPenetrant

1.1. Readily penetrateReadily penetrate

2.2. Non volatileNon volatile

3.3. Be removed easilyBe removed easily

4.4. Ability to spread out Ability to spread out in very thin filmsin very thin films

5.5. Have great brilliance Have great brilliance of color of color

6. Be inert6. Be inert

7. Odorless7. Odorless

8. Nonflammable8. Nonflammable

9. Nontoxic9. Nontoxic

10. Low in cost10. Low in cost

11. Have permanence 11. Have permanence of colorof color

Physical properties of Physical properties of PenetrantsPenetrants

ViscosityViscosity Property of a fluid by which it offers resistance to Property of a fluid by which it offers resistance to

relative motion between its different layers.relative motion between its different layers. 1 stoke = 1 cm2/sec, 1CST = 10-2 cm2/sec1 stoke = 1 cm2/sec, 1CST = 10-2 cm2/sec Optimum viscosity level is Optimum viscosity level is 5 CST5 CST..

Wetting abilityWetting ability Ability to wet surface or measure of contact area.Ability to wet surface or measure of contact area. Contact angle is formed by the solid/liquid Contact angle is formed by the solid/liquid

interface.interface. Liquids wet surfaces when the contact angle is < Liquids wet surfaces when the contact angle is <

90.90. The lesser the contact angle (< 5 ), the higher the The lesser the contact angle (< 5 ), the higher the

wetting ability.wetting ability.

Physical propertiesPhysical propertiesSurface tension (ST)Surface tension (ST) Force acting per unit Force acting per unit

length is called the ST.length is called the ST. High ST solvents will High ST solvents will

easily dissolve dyes.easily dissolve dyes. Low ST provides Low ST provides

penetration & spreading penetration & spreading properties.properties.

VolatilityVolatility Evaporation help to Evaporation help to

intensify dye brilliance & intensify dye brilliance & also prevent excessive also prevent excessive spreading of indications. spreading of indications.

Penetrants should be non-Penetrants should be non-volatile liquids.volatile liquids.

FlammabilityFlammability Penetrants have high Penetrants have high

flash point (should not be flash point (should not be < 57C).< 57C).

Chemical activityChemical activity

Penetrants should non-Penetrants should non-corrosive towards test corrosive towards test materials & storage materials & storage containers.containers.

Mechanisms of Mechanisms of penetration:penetration:

Penetration depends on:Penetration depends on:

Surface condition of the partSurface condition of the part Type of penetrantType of penetrant Temperature of part/penetrantTemperature of part/penetrant

TYPES OF PENETRANTSTYPES OF PENETRANTS According to the dye they According to the dye they

are usingare using, are classified into 3 , are classified into 3 types:types:

Visible dye penetrantVisible dye penetrant: : A A brightly colored dye that is brightly colored dye that is visible under normal lightning visible under normal lightning conditionsconditions

Fluorescent dye penetrantFluorescent dye penetrant: : Almost colorless dye, emits Almost colorless dye, emits visible light rays when viewed visible light rays when viewed under black light.under black light.

Dual sensitivity penetrantDual sensitivity penetrant: : It It contains both a visible dye & a contains both a visible dye & a fluorescent dye for more fluorescent dye for more sensitivity.sensitivity.

EXCESS PENETRANT EXCESS PENETRANT REMOVALREMOVAL

Penetrant removal is the most imp. step Penetrant removal is the most imp. step in PT.in PT.

Over washing will remove penetrant from Over washing will remove penetrant from flaws. flaws.

Under washing will leave too much Under washing will leave too much penetrant & cause interfering background penetrant & cause interfering background & hide indication.& hide indication.

According toAccording to the process used to the process used to remove the excess penetrantremove the excess penetrant, are , are classified into 3 types:classified into 3 types:

1. WATER WASHABLE 1. WATER WASHABLE PENETRANT PENETRANT

These are either self These are either self emulsifying or emulsifying or removable with plain removable with plain water.water.

1.1. Dipping part into Dipping part into water tank or water tank or

2.2. by spraying with low by spraying with low pressure water.pressure water.

Advantages:Advantages:

1.1. Easily washed with waterEasily washed with water2.2. Good for small & rough Good for small & rough

specimensspecimens3.3. Good on keyways & threadsGood on keyways & threads4.4. Single step processSingle step process5.5. Relatively inexpensive Relatively inexpensive

Limitations:Limitations:

1.1. Not reliable for detecting shallow Not reliable for detecting shallow defectsdefects

2.2. Easily over washedEasily over washed3.3. Penetrant subjected to water Penetrant subjected to water

contamination contamination

2. Post-Emulsified 2. Post-Emulsified Penetrant (PEP)Penetrant (PEP)

Requires emulsifier to Requires emulsifier to make penetrant water make penetrant water washable.washable.

Removed by dipping Removed by dipping the part into emulsifier the part into emulsifier followed by dipping in followed by dipping in water tanks or by water water tanks or by water spraying.spraying.

Emulsification times Emulsification times depends on depends on

penetrant & emulsifier, penetrant & emulsifier, test surface & type of test surface & type of rinse. rinse.

• Two types of PEP:Two types of PEP:Lipophilic or oil base materialLipophilic or oil base materialHydrophilic or water base materialHydrophilic or water base materialThe hydrophilic method is more sensitive than The hydrophilic method is more sensitive than the Lipophilic post emulsifiable method.the Lipophilic post emulsifiable method.

AdvantagesAdvantages

1.1. Good on wide shallow defectsGood on wide shallow defects

2.2. Easily water washed after Easily water washed after emulsificationemulsification

3.3. High sensitivity for fine High sensitivity for fine defectsdefects

4.4. Short penetration timeShort penetration time

5.5. Cannot be easily over washedCannot be easily over washed

LimitationsLimitations

1.1. Two step processTwo step process

2.2. Difficult to remove Difficult to remove from threads, from threads, keyways & rough keyways & rough surfacessurfaces

Solvent Removable Solvent Removable Penetrant (SRP)Penetrant (SRP)

These must be These must be removed with a removed with a solvent & are solvent & are available in available in pressurized spray pressurized spray cans.cans.

Just dampen not Just dampen not saturate the lint free saturate the lint free cloth with the solvent.cloth with the solvent.

SRPSRP Advantages:Advantages:

1.1. PortabilityPortability

2.2. No water requiredNo water required

3.3. Good for spot Good for spot checkingchecking

Limitations:Limitations:

1.1. Flammable materialsFlammable materials

2.2. Time consumingTime consuming

3.3. Difficult on rough Difficult on rough surfacessurfaces

DRYING OF THE PARTDRYING OF THE PART Thoroughly dry the part before Thoroughly dry the part before

developer is applied.developer is applied.

1.1. The part should be placed in a drying The part should be placed in a drying oven at temp. of 180F (82C) for oven at temp. of 180F (82C) for drying.drying.

2.2. Drying with a blast of high velocity air.Drying with a blast of high velocity air.

Too long drying will reduce the Too long drying will reduce the sensitivity.sensitivity.

DEVELOPERS & DEVELOPERS & APPLICATIONAPPLICATION

Dry powderDry powder

1.1. Least sensitive, Least sensitive, inexpensive & easy to inexpensive & easy to apply. These are white, apply. These are white, fluffy powders.fluffy powders.

2.2. Applied by dipping parts in Applied by dipping parts in dry powder or dry powder or

3.3. by using a puffer to dust by using a puffer to dust the parts.the parts.

4.4. Developer is blown on Developer is blown on part.part.

5.5. By Electrostatic powder By Electrostatic powder spray guns.spray guns.

Water-solubleWater-soluble DeveloperDeveloper Chemicals are Chemicals are

dissolved in water & dissolved in water & form a layer when form a layer when water is evaporated water is evaporated away.away.

Applied by spraying it Applied by spraying it on the part.on the part.

If the parts are not If the parts are not dried quickly, the dried quickly, the indications will be indications will be blurred & indistinct.blurred & indistinct.

Wet DeveloperWet Developer Water SuspendibleWater Suspendible Insoluble particles suspended in Insoluble particles suspended in

water & requires frequent stirring or water & requires frequent stirring or agitation.agitation.

Film Type DeveloperFilm Type Developer Used when a permanent record is Used when a permanent record is

required.required.

NON AQUEOUS DEVELOPERNON AQUEOUS DEVELOPER

Suspend the Suspend the developer in a volatile developer in a volatile solvent & applied solvent & applied with a spray gun with a spray gun (portable).(portable).

Since highly volatile Since highly volatile solvent, forced drying solvent, forced drying is not required. is not required.

Provides highest Provides highest sensitivity.sensitivity.

QUALITY CONTROL OF QUALITY CONTROL OF PENETRANT TEST PENETRANT TEST

MATERIALSMATERIALS1.1. CRACKED ALUMINIUM COMPARATOR BLOCKCRACKED ALUMINIUM COMPARATOR BLOCK

Used for comparisons & for qualification of Used for comparisons & for qualification of penetrant procedures & not for absolute penetrant procedures & not for absolute evaluations. evaluations.

Block is heated to a temp. bet. 510 to 525 0C & is Block is heated to a temp. bet. 510 to 525 0C & is then quenched in cold water to produce net work of then quenched in cold water to produce net work of fine cracks. fine cracks.

A groove is across the center of face & 1/2 is A groove is across the center of face & 1/2 is marked “A & B’.marked “A & B’.

The indications of cracks shall be compared bet. The indications of cracks shall be compared bet. “A” & “B”. If the indications are same the “A” & “B”. If the indications are same the proposed procedure shall be considered qualify.proposed procedure shall be considered qualify.

Application of Al. blockApplication of Al. block

To check the quality of different LPT To check the quality of different LPT systems.systems.

To compare different penetrants (& To compare different penetrants (& different developers) of different different developers) of different manufacturer makes.manufacturer makes.

To qualify a PT system at different To qualify a PT system at different temperatures.temperatures.

Sensitivity tests.Sensitivity tests.

LIGHTINGLIGHTING

– VisibleVisible

1.1. Visible Visible penetrantpenetrant requires light source in requires light source in visible frequency range visible frequency range (white light). (white light).

2.2. Light intensity of at Light intensity of at least 100 foot-candles least 100 foot-candles or 1000 lux. or 1000 lux.

3.3. Light can be provided Light can be provided by incandescent bulb.by incandescent bulb.

- Ultraviolet Light (UV)Ultraviolet Light (UV)

1.1. UV lights are used with UV lights are used with fluorescent penetrants. fluorescent penetrants.

2.2. Light in UV range has a Light in UV range has a short wavelength. short wavelength.

3.3. A filter over the mercury A filter over the mercury vapor lamp limits the vapor lamp limits the wavelength emitted with wavelength emitted with 3650 A. 3650 A.

Acceptance criteriaAcceptance criteria

All surfaces to be examined shall be free All surfaces to be examined shall be free of:of:

1)1) Relevant linear indications.Relevant linear indications.

2)2) Relevant rounded indications >3/16” Relevant rounded indications >3/16” (5mm).(5mm).

3)3) 4 or more relevant rounded indications 4 or more relevant rounded indications are separated by 1/16”(1.5mm) or are separated by 1/16”(1.5mm) or less(edge to edge).less(edge to edge).

Note: A linear indication is one having a Note: A linear indication is one having a length>3 times the width.length>3 times the width.

CAUSES OF IRRELEVANT & FALSE CAUSES OF IRRELEVANT & FALSE INDICATIONS.INDICATIONS.

Irrelevant indications are actual Irrelevant indications are actual discontinuities ( by design)- press fits, discontinuities ( by design)- press fits, braze bond lines & naturally occurring. braze bond lines & naturally occurring.

False IndicationFalse Indication - indication caused by - indication caused by poor washing.poor washing.

1)1) Penetrant on operator’s handsPenetrant on operator’s hands

2)2) Contamination of developerContamination of developer

3)3) Penetrant transferred to clean Penetrant transferred to clean specimen from other indications &specimen from other indications &

4)4) Penetrant on inspection table. Penetrant on inspection table.

RECORDING OF RECORDING OF INDICATIONSINDICATIONS

1. 1. SketchesSketches Sketches provide the simples method of recording indications.Sketches provide the simples method of recording indications.

2. Tape Transfer2. Tape Transfer tape is laid down lightly over indication & lift tape from surface. tape is laid down lightly over indication & lift tape from surface.

3. 3. Plastic Film DeveloperPlastic Film Developer It is sprayed, solvent carrier acting to draw penetrant into the film. It is sprayed, solvent carrier acting to draw penetrant into the film. Provides a permanent record of discontinuity.Provides a permanent record of discontinuity.

4. PHOTOGRAPHY4. PHOTOGRAPHY The best method of recording penetrant indications is by The best method of recording penetrant indications is by

photography. photography. The picture will provide the location & orientation of the The picture will provide the location & orientation of the

discontinuity.discontinuity.

Welding DefectsWelding Defects

Penetrants can detect given Penetrants can detect given discontinuitiesdiscontinuities

1.1. PorosityPorosity

2.2. LOP (On single sided weld joints)LOP (On single sided weld joints)

3.3. Crater cracksCrater cracks

4.4. LOF (as toe of weld)LOF (as toe of weld)

5.5. Crack at heat-affected zone.Crack at heat-affected zone.