3001 Rev.0 - Liquid Penetrant Testing Level 1 & 2 Combined - Note Book

LIQUID PENETRANT TESTING LEVEL 1 & 2 COMBINED NOTE BOOKNASA-PT-3001 REV. 0

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TABLE OF CONTENTS

CHAPTER 1 QUALIFICATION, CERTIFICATION AND AUTHORIZATION .............................. 2CHAPTER 2 BASIC PRINCIPLES .......................................................................................... 5CHAPTER 3 VISIBLE METHODS ....................................................................................... 19CHAPTER 4 FLUORESCENT METHODS............................................................................ 28CHAPTER 5 SPECIAL PURPOSE CHEMICALS.................................................................... 39CHAPTER 6 INLINE SYSTEMS .......................................................................................... 41CHAPTER 7 CONTROL CHECKS........................................................................................ 43CHAPTER 8 HEALTH AND SAFETY ................................................................................... 50SUMMARY OF DISCONTINUITIES ...................................................................................... 56INTERPRETATION VS. EVALUATION .................................................................................. 57


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CHAPTER 1 QUALIFICATION, CERTIFICATION AND AUTHORIZATION

SNT-TC-1A & ISO 9712It is important that the technician be qualified and certified in the NDT method before thetechnique is used and the test results evaluated.

The American Society for Nondestructive Testing recommends the use of their documentRecommended Practice No SNT-TC-1A.

The International Standards Organization requires the use of their Specification, namelyISO 9712.

These documents provides the employer with the necessary guidelines to properly qualify andcertify the NDT technician in all methods.

To comply with these documents, the employer must establish a written practice which describesin detail how the technician will be trained, examined and certified.

These documents specifies the initial number of hours of classroom instruction and months orhours of experience necessary to be certified as an NDT testing technician. The main differencebetween these documents are that:

SNT-TC-1A requires Company (Employer) Certification, and

ISO 9712 requires Certification by a Body such as PCN or CSWIP.


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LEVELS OF QUALIFICATIONLevel 1

An individual certified to Level 1 has demonstrated competence to carry out NDT according towritten instructions and under the supervision of Level 2 or Level 3 personnel. Within the scopeof the competence defined on the certificate, Level 1 personnel may be authorized by theemployer to perform the following in accordance with NDT instructions:

set up NDT equipment; perform the tests; record and classify the results of the tests according to written criteria; report the results.

Level 1 certified personnel shall neither be responsible for the choice of test method ortechnique to be used, nor for the evaluation of test results.

Level 2

An individual certified to Level 2 has demonstrated competence to perform NDT according toNDT procedures. Within the scope of the competence defined on the certificate, Level 2personnel may be authorized by the employer to:

select the NDT technique for the testing method to be used; define the limitations of application of the testing method; translate NDT codes, standards, specifications, and procedures into NDT instructions

adapted to the actual working conditions; set up and verify equipment settings; per form and supervise tests; interpret and evaluate results according to applicable standards, codes, specifications or

procedures; carry out and supervise all tasks at or below Level 2; provide guidance for personnel at or below Level 2; report the results of NDT.

Level 3

An individual certified to Level 3 has demonstrated competence to perform and direct NDToperations for which he is certified. Level 3 personnel have demonstrated:

the competence to evaluate and interpret results in terms of existing standards, codes,and specifications;

sufficient practical knowledge of applicable materials, fabrication, process, and producttechnology to select NDT methods, establish NDT techniques, and assist in establishingacceptance criteria where none are otherwise available;

a general familiarity with other NDT methods.


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Within the scope of the competence defined on the certificate, Level 3 personnel may beauthorized to:

assume full responsibility for a test facility or examination centre and staff establish, review for editorial and technical correctness, and validate NDT instructions

and procedures interpret standards, codes, specifications, and procedures designate the particular test methods, procedures, and NDT instructions to be used carry out and supervise all tasks at all levels provide guidance for NDT personnel at all levels.

EXAMINATION BREAKDOWNThe end of Course examination (SNT-TC-1A), at NASA will comprise of the following:General examination:

Closed book. 40 Multi-choice questions. 1 Hour.

Specific examination: 20 Multi-choice questions. 5 Open Code Book Questions. (10 points) 1 Hour.

Practical examination:

Pre-Test Calibrations: Complete a Calibration Procedure as allocated by examiner. 30 minutes.

Practical 1:Visible, Solvent Removable Method with Non-Aqueous Wet Developer on a welded sample. Complete a Written Instruction. Fill out a Test Report. 3 Hours.

Practical 2:Fluorescent, Water-washable Method with Non-Aqueous Wet Developer on a welded sample. Complete a Technique sheet. Fill out a Test Report. 2 Hours.

A minimum of 70% must be scored on each segment of the exam with an aggregate of 80% inorder to pass.


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CHAPTER 2 BASIC PRINCIPLES

INTRODUCTIONLiquid penetrant testing is a Non-destructive means of locating surface discontinuities in anysolid, non-porous material. The method is based on capillary action in which the liquid is elevatedor depressed where it is in contact with a solid. Effectiveness is mainly controlled by thetechnicians ability and determination to follow the specifications set out in the procedure. Thetest materials (penetrants, developers, cleaners) and procedures for Liquid Penetrant Testing aredesigned to facilitate capillary action and make the results visible and interpretable.The method is used to inspect a variety of product forms including castings, forgings, and welds.Many different industries use liquid penetrant inspection for determining a component's fitness-for-use. Some examples of industries that use liquid penetrant inspection are the structural steel,automotive, petrochemical, power generation, and aerospace industries.

PENETRANT PRINCIPLESWhen a dye is added to a liquid with a certain combination of properties, the liquid is calledpenetrant, penetrant dye or in some specifications just dye. The ability of a penetrant to coverthe surface and penetrate the openings depends on Viscosity, Cohesion, Adhesion, Surfacetension, Wetting Ability (wettability) and Capillary action.

VISCOSITYViscosity is a measure of a liquids resistance to a change in physical shape and is related tointernal friction. The viscosity of a liquid decreases as the temperature is raised and viscosityincreases as the temperature is lowered. Viscosity has no effect on Capillary action (penetratingability). Some highly viscous fluids, such as molasses, have very good penetrating ability, whilesome low viscosity liquids, such as pure water, have very poor penetrating ability. However, froman application viewpoint, viscosity affects the speed with which a penetrant enters adiscontinuity. Viscosity also determines how much penetrant will remain on a part surface duringthe dwell period. High viscosity penetrants cling to the surface, requiring increased effort forremoval. Very thin penetrants (low viscosity) may drain from the part surface so quicklyinsufficient penetrant remains to enter into discontinuities.There are in existence, THIXOTROPIC penetrants which have a two-stage viscosity. Thesepenetrants are in a high viscosity (thick) state when stored and when worked (i.e. painted) on tothe test surface the penetrant is broken down into its second stage, a more fluid state, by theshearing action of brushing. This is the same action as non-drip paint.Points of interest:

Longer contact times are required. They are ideal for overhead work. They are often used on high temperature applications (up to 200C)

Note: above 50C fluorescent dyes start to degrade (lose fluorescence) due to heat fade andhence high temperature work is nearly always colour contrast.


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COHESION AND ADHESIONThese properties are easily explained with the example of a straw inserted in water.The Capillary forces draws the liquid into the straw higher than the actual level of water aroundthe straw. When the straw is inserted, the molecules enter the straw and attract other nearbymolecules and pulling then up the straw by cohesion. Cohesion can therefore be said as theliquids molecular attraction. This process continues to rise until the pull of surface tension isequalized. Adhesion is the force that prevents the liquid to fall back down the straw. Adhesioncan be said to be the attraction between the material of the straw and the liquid.

SURFACE TENSIONIt can be defined as the force required to expand (or pull apart) the surface of a liquid. Thesurface of a liquid exhibits certain features resembling the properties of a stretched elasticmembrane. These features are due to the cohesive forces holding the surface moleculestogether, hence the term surface tension. The very high surface tension of water allows certaininsects to stand on the surface of the water and the surface tension of water can even supportsteel paper clips even though steel is much denser than water and is not supposed to float. Theforces drawing surface molecules together can be very strong. These forces, or surface tension,cause a droplet of liquid to have a spherical shape.


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WETTING ABILITYWhen a liquid comes into contact with a solid surface, the cohesive force responsible for surfacetension competes with or is countered by the adhesive force between the liquid molecules andthe solid surface. These forces determine the contact angle the liquid forms with the surface. Thecontact angle is the measured angle a drop of liquid makes with a solid surface. If the contactangle is zero the liquid will wet and spread. If the contact angle is 90-degrees or more the liquidwill not wet the surface and will remain as a rounded drop.

Capillary Action (Capillarity)It is one of the most important properties of the penetrant to consider. Capillarity is the ability ofa liquid to flow in narrow spaces without the assistance of, and in opposition to, external forceslike gravity. Capillary action is defined as the tendency for a liquid to penetrate or migrate intosmall openings, such as cracks, pits, or fissures. The capillary action forces are very strong; in fact,if a penetrant test were being performed on a specimen in an overhead position, the penetrantwould be drawn into the opening against the force of gravity. A good penetrants force isstronger than gravity and the discontinuities will be detected even though they may be in anoverhead specimen.


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PENETRANT PROPERTIESOther properties have to be considered with regards to quality and safety regulations, such as:FLASH POINTFlash point is the lowest temperature at which vapors of a substance ignite in air when exposedto a flame. The flash point does not affect the performance of a penetrant. High flash points aredesirable to reduce the hazard of fire. Generally, it is recommended that penetrant materialshave a flashpoint no less than 93C.

VOLATILITYThe vapor pressure or boiling point of a liquid characterizes its volatility. It is associated with theevaporation rate of liquids and is desirable for penetrant materials to have a low volatility, i.e., ahigh boiling point. However, in the case of petroleum products, viscosity increases as the boilingpoint goes up. In this group of materials, the lower viscosity is preferred because they requireless penetrating time. Still, for practical purposes, high volatility should be avoided beforeviscosity becomes a problem. High volatility results in a loss of penetrant in open tanks and canresult in penetrant drying on a part during the penetrant dwell, leaving a film difficult to remove.Entrapped, highly volatile penetrant would also have a tendency to dry or lose its liquidproperties, resulting in failure to bleed back out of a discontinuity and to produce an indication.In general, low volatility provides four advantages:

Low economic loss due to low evaporation loss. Low fire hazard because few flammable vapors form above the liquid. Low toxicity because of low hazardous vapor concentrations in the test area. Uniform removal and fluorescent properties because of minimal evaporation.

CHEMICAL INERTNESSPenetrant materials may cause deterioration and damage to materials that react tohydrocarbons. Penetrant materials shall not react with the materials to be inspected. It isnecessary for the penetrant, emulsifier, and developer material be chemically inert relative to theparts being inspected. Most oil based materials meet this requirement; however, watercontamination of many oils may cause the mixture to become alkaline. This is one of the reasonswhy water contamination must be avoided. While oily penetrant materials are generally inert tomost metals, there is no one material that can be formulated for all parts. Chemical reactivity ofpenetrant materials must be considered whenever a new application is encountered. Somerubber (natural and synthetic) and plastic (transparent and opaque) parts are susceptible toattack by the solvents and oils in the penetrant materials. Some metals can be degraded atelevated temperatures by the trace amounts of sulfur or chlorine in conventional penetrants.

TOXICITYIt is the measure of adverse effects on humans resulting from contact with the material. It appliesto any abnormal effects ranging from nausea and dermatitis through dysfunction of majororgans, such as the liver or kidneys. It is essential for penetrant materials to be nontoxic. Inqualifying penetrant materials for the QPL, the manufacturer must submit a certified statementidentifying each ingredient in the product by a recognizable chemical or trade name. TheUSAF Occupational and Environmental Health Laboratory has to evaluate this information fortoxicity before the material is listed as a qualified product.


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SOLVENT ABILITYThe visibility of indications depends upon the fluorescent or visible dye dissolved in the penetrantoils. The oils used in penetrants must have good solvent properties to dissolve and hold the dyein solution. It must maintain the dye in solution under the wide range of temperaturesencountered during transit and storage of the penetrant. If even a small amount of separationoccurs, recombination may be very difficult or impossible, resulting in decreased penetrantperformance.

REMOVABILITYThis term describes two conflicting requirements for a penetrant:

the ability to be removed from a surface leaving little or no residual background resistance to being removed from discontinuities

The removability would be subject to the viscosity of the material.

WATER TOLERANCEWhen penetrants are used in open tanks some water contamination is inevitable.Post-emulsifiable penetrants are inherently tolerant to water intrusion. Since they are oil basedmaterials, any extraneous water will settle to the bottom of the tank. Although theirperformance is not degraded, corrosion of the tank can occur. However, water washablepenetrants contain emulsifiers and will combine with water. They can tolerate the addition ofsmall amounts of water without losing their properties. However, penetrant has to be checkedcontinually for water content not to exceed manufacturers specifications/ requirements.

DENSITYPenetrant density is approximately 0.91 g/cm3, compared to water which is 1g/cm3. Therefore donot use the bottom third of the tank due to contaminants sinking to the bottom of the tank.Some application specifications require tanks to be drained and cleaned every 12 months. Notedue to proximity of washing stations the most common contaminant is water.

PENETRANT SENSITIVITYThe term sensitivity, when used to describe a penetrant performance characteristic, is theability to produce indications from very small, tight cracks. This characteristic involves thecombined properties of penetrating ability and brightness. The flaw opening in discontinuities isusually restricted, and the void volume is such that only a very small amount of penetrant can beentrapped. The penetrant must enter and exit the flaw with enough dye to produce a noticeableindication.


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HISTORYLiquid penetrant inspection is one of the oldest non-destructive inspection methods. It was firstused in the railroad maintenance shops in the late 1800s. Parts to be inspected were immersed inused machine oil. After a suitable immersion time, the parts were withdrawn from the oil and theexcess surface oil wiped off with rags or wadding. The part surfaces would then be coated withpowdered chalk or a mixture of chalk suspended in alcohol (whiting). Oil trapped in cracks orflaws would bleed-out causing a noticeable stain in the white chalk coating. This became knownas the oil-and-whiting method.

As can be expected, there were many problems with this early technique. There was a generallack of consistency, since there were no established procedures or standards and the dwell anddevelopment times were left up to the user. The oil-and-whiting method was more-over replacedby magnetic particle inspection on steel and ferrous parts in 1930.

However, industries using non-ferromagnetic metals, especially aircraft manufacturers, needed amore reliable and sophisticated tool than discoloured machine oil and chalk. In 1941, fluorescentdye materials were added to highly penetrating oil by Robert Switzer to make a penetrantmaterial. Coloured dyes, primarily red, were introduced in the 1940s by Rebecca Smith (a.k.a.Becky Starling), Lloyd Stockman and Elliot Brady. Since then, a large number of penetrant systemsor families have evolved. These include developments in various types and concentrations of dyematerials, types of penetrating oils and additives, materials and methods for removing the excesssurface penetrant, and various materials and forms of developing agents.

TEST PROCEDURESApproved procedures for liquid penetrant testing are formulated from analysis of the testspecimen, review of its past history, experience and information available concerningdiscontinuities in like or similar articles. It is the responsibility of personnel conducting orchecking tests to ensure that the test procedures are adequately performed, and that the testobjective is accomplished. Procedures found incorrect or inadequate must be brought to theattention of responsible supervision for correction.

TEST OBJECTIVEThe objective of liquid penetrant testing is to ensure maximum reliability by providing a meansof:

Obtaining a visual image related to the discontinuity on the surface of the specimen undertest.

Disclosing the nature of the discontinuity without impairing the material. Separating acceptable and unacceptable material in accordance with predetermined

standards.


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ADVANTAGES (7 listed):The liquid penetrant method has a number of outstanding advantages within its field ofusefulness that is, on ferromagnetic and non-ferromagnetic materials. Some of these are thefollowing:

Since discontinuities open to the surface are almost always more detrimental to thestrength of parts than similar discontinuities not open to the surface, inspection isconcentrated at the most vulnerable area.

Tests are quick, easily applied, and penetrant materials and associated equipmentrelatively inexpensive.

Liquid penetrants are very sensitive to fine surface cracks. Liquid penetrants can be applied to the surface of the objects of complex shape. Flaw indications will remain visible until wiped off, therefore, there is no need to rework

defective parts immediately. In fact, if salvage is practical, parts can often be reworkedwith the location and extent of discontinuities still showing, thus simplifying accuraterepair. Parts should be re-inspected after repairing discontinuities.

Large areas and large volumes of parts/materials can be inspected rapidly and at lowcost.

Aerosol spray cans make penetrant materials very portable.

DISADVANTAGES (14 listed):Although the method has many desirable and attractive advantages, it has, as does everymethod, certain limitations. These, the operator must be aware of, and take into account byobserving the precautions which they dictate. Some of the disadvantages are the following:

The surface must be clean and dry before the penetrant is applied, otherwise surfacecontamination may interfere with the tests.

Only surface breaking defects can be detected. Only materials with a relatively nonporous surface can be inspected. Metal smearing from machining, grinding, and grit or vapor blasting must be removed

prior to LPI. The inspector must have direct access to the surface being inspected. Surface finish and roughness can affect inspection sensitivity. Multiple process operations must be performed and controlled. Post cleaning of acceptable parts or materials is required. Chemical handling and proper disposal is required. The penetrant should be used on objects that are near room temperature. Low

temperatures can cause the penetrant to become highly viscous and high temperaturescan cause the penetrant to evaporate.

Shallow or broad flaws are difficult to detect since the penetrant is easily removed fromthem accidentally when the excess penetrant is being removed.

Certain materials may be permanently stained by the liquids used for inspection. Some materials may be permanently damaged due to certain strong chemicals existing

in the penetrant materials and therefor prior to inspection, the requirements should bedetermined for use of special liquids and materials.

It is often difficult to remove all the penetrant from the object at the conclusion of aninspection. In some situations, removal of penetrant materials are crucial and this mightinterfere with further use or processing.


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BASIC PENETRANT TESTING PROCESSA basic sequence of operations for inspection of a specimen would be:

A thorough pre-cleaning to ensure all surface contaminantsare removed.

Apply penetrant by brushing, spraying, flooding, dipping, etc. Allow penetrant to dwell in order for the penetrant to flow

into discontinuities. Clean off excess penetrant from the surface. Apply a thin, even layer of developer and allow a developer

dwell time for penetrant to bleed out from discontinuities. Inspect for indications under correct light requirements. Post cleaning should be done to ensure all penetrant materials

are removed from the surface.


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CLASSIFICATION OF PENETRANT MATERIALS AND PROCESSESThe various combinations of liquid penetrant materials that are commercially available and usedchanges rapidly as new and better materials are formulated. The classification of method isdescribed by the materials used and cleaning processes.Below is a table that shows all types and methods of liquid penetrant materials and how they areclassified.

TYPEType I Fluorescent Dye PenetrantType II Visible Dye PenetrantType III Dual Mode

METHOD OF REMOVALMethod A Water WashableMethod B Post-Emulsifiable, Lipophilic (oil based)Method C Solvent removableMethod D Post-Emulsifiable, Hydrophilic (water based)

SENSITIVITYLevel 1/2 Very LowLevel 1 LowLevel 2 MediumLevel 3 HighLevel 4 Ultra high

DEVELOPERForm a Dry powderForm b Water SolubleForm c Water SuspendibleForm d Non-aqueous wet for fluorescent dye Type IForm e Non-aqueous wet for visible dye Type IIForm f Special Application

SOLVENT CLEANER / PENETRANT REMOVERClass 1 HalogenatedClass 2 Non-halogenatedClass 3 Special Application


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TERMINOLOGYAqueous developer: See Wet developer.Background: The surface on which an indication is viewed. It may be the

natural surface of the test object, or it may be thedeveloper coating on the surface. This background maycontain traces of unremoved penetrant (fluorescent orvisible), which if present, can interfere with the visibility ofindications.

Background fluorescence: Fluorescent residue observed over the general surface ofthe test object during a fluorescent penetrant test.

Bath: Term used colloquially to designate the liquid penetranttesting materials into which test objects are immersedduring the testing process.

Black light: See Ultraviolet radiation.Bleedout: The action of the entrapped penetrant in spreading out

from surface discontinuities to form an indication.Blotting: The action of the developer in soaking up penetrant from a

surface discontinuity, so as to cause maximum bleed-outof penetrant for increased contrast and sensitivity.

Capillary action: The tendency of liquids to penetrate or migrate into smallopenings, such as cracks, pits or fissures.

Clean: Free of interfering solid or liquid contamination.Colour contrast penetrant: See Visible dye penetrant.Comparative reference block: An intentionally cracked metal block having two separate

but adjacent areas for the application of differentpenetrants so that a direct comparison of their relativeeffectiveness can be obtained. Can also be used toevaluate penetrant test techniques and test conditions.

Contact emulsifier: A fluid that begins emulsifying penetrant on simple contactwith the penetrant. Usually oil based (Lipophilic).

Contrast: The difference in visibility (luminance or coloration)between an indication and the surrounding surface.

Dark adaptation: The adjustment of the eyes when one passes from a brightto a darkened area.

Defect: A discontinuity that interferes with the usefulness of anobject. A fault in a material or test object that isdetrimental to its serviceability.

Detergent remover: A penetrant remover that is a solution of a detergent inwater. Also see Hydrophilic emulsifier.

Developer: A material that is applied to the test object surface afterexcess penetrant has been removed and that is designedto enhance the penetrant bleed-out to form indications.The developer may be a fine powder, a solution that dries


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to a fine powder or a suspension (in solvent, water alcohol,etc.) that dries leaving an absorptive film on the testsurface.

Developing time: The time between the application of the developer and theexamination of the test object for indications. The elapsedtime necessary for the applied developer to bring outindications from penetrant entrapments. Also calleddevelopment time.

Discontinuity: An interruption in the normal physical structure orconfiguration of an object, such as cracks, forging laps,seams, inclusions, porosity, etc. A discontinuity may ormay not affect the usefulness of the test object.

Drag-out: The loss of penetrant materials from a tank as a result oftheir adherence to the objects being processed.

Drain time: That portion of the penetrant testing processes duringwhich the excess penetrant, emulsifier, detergent removeror developer is allowed to drain from the test object.

Dry developer: A fine dry powder developer that does not use a carrierfluid.

Drying oven: An oven used for drying rinse water from test objects.Drying time: The time allotted for a rinse test object to dry.Dual sensitivity penetrant: A penetrant that contains a combination of visible and

fluorescent dyes.Dwell time: The total time that the penetrant or emulsifier is in contact

with the test surface, including the time required forapplication and the drain time. Also see Emulsificationtime.

Electrostatic spraying: A technique of spraying wherein the material beingsprayed is given high electrical charge, while the testobject is grounded.

Emulsification time: The period of time that an emulsifier is permitted tocombine with the penetrant before removal. Also calledemulsifier dwell time.

Emulsifier: A liquid that combines with an oily penetrant to make thepenetrant water washable. Also see Hydrophilic emulsifierand lipophilic emulsifier.

Evaluation: The process of determining the severity of the conditionafter the indication has been interpreted. Evaluation leadsto determining whether the object is acceptable,salvageable or rejectable.

False indication: An indication caused by improper processing. Distinct fromnon-relevant indication.

Flash point: The lowest temperature at which a volatile flammableliquid will give off enough vapor to make a combustible


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explosive mixture in the air space surrounding the liquidsurface.

Flaw: See Discontinuity.Fluorescence: The emission of visible radiation by a substance as the

result of, and only during, the absorption of ultravioletradiation.

Fluorescent penetrant: A testing penetrant that is characterized by its ability tofluoresce when exited by ultraviolet radiation.

Hydrophilic emulsifier: A water based agent that, when applied to an oilypenetrant, renders the penetrant water washable. Can beused as a contact emulsifier, but more often the emulsifieris added to the water rinse and accompanied by someform of mechanical agitation or scrubbing to removeexcess penetrant. Sometimes called a hydrophilic remover.

Indication: That which marks the presence of a discontinuity, as theresult of detectable bleed-out of penetrant from thediscontinuity.

Inspection: The visual examination of a test object after completion ofthe penetrant processing steps.

Interpretation: The determination of the significance of indications fromthe standpoint of whether they are relevant ornon-relevant.

Leak testing: A technique of liquid penetrant testing in which thepenetrant is applied to one side of the surface, while theother side is tested for indications that would indicate aleak or void.

Lipophilic emulsifier: An oil based agent that, when applied to an oily penetrant,renders the penetrant water washable. Usually applied toa contact emulsifier.

Non-aqueous wet developer: A developer in which the developing powder is applied asa suspension in a quick drying solvent. Also called solventdeveloper.

Non-fluorescent penetrant: See Visible dye penetrant.Non-relevant indication: An indication that is not or cannot be associated with a

discontinuity.Penetrability: The property of a penetrant that causes it to find its way

into very fine openings, such as cracks.Penetrant: A liquid capable of entering discontinuities open to the

surface, and which is adapted to the testing process bybeing made highly visible in small traces. Fluorescentpenetrants fluoresce brightly under ultraviolet radiation,while the visible penetrants are intensely coloured to benoticeable under visible light.

Penetration time: See Dwell time.


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Post-emulsification: A penetrant removal technique using a separateemulsifier.

Post-emulsifiable penetrant: A penetrant that requires the application of a separateemulsifier to render the surface penetrant waterwashable. Can be removed by applying a solvent remover.

Pre-cleaning: The removal of surface contaminants or smeared metalfrom the test object so that they cannot interfere with thepenetrant testing process.

Quenching of fluorescence: The extinction of fluorescence by causes other thanremoval of ultraviolet radiation (the exciting radiation).

Rinse: The process of removing liquid penetrant testing materialsfrom the surface of a test object by washing or floodingwith another liquid usually water. Also called wash.

Self emulsifiable: See Water washable penetrant.Sensitivity: The ability of the penetrant process to detect surface

discontinuities.Solvent developer: See Non-aqueous wet developer.Solvent removed: A penetrant removal technique wherein the excess

penetrant is wiped from the test surface with a solventremover.

Solvent remover: A volatile liquid used to remove excess surface penetrantfrom the test object. Sometimes call penetrant remover.

Surface tension: That property of liquids which, because of molecularforces, tends to bring the contained volume into a formhaving the least superficial area.

System: With respect to liquid penetrant testing materials, acombination of liquid penetrant and emulsifier that arefurnished by same manufacturer and are qualifiedtogether. For water washable and solvent removable liquidpenetrants, a system consists of the liquid penetrant only.

Ultraviolet radiation Light radiation in the near ultraviolet range (for liquidpenetrant testing):(UV-A) of wavelengths (320 to 400 nm),just shorter than visible light.

Ultraviolet radiation filter: A filter that transmits near ultraviolet radiation whilesuppressing visible light and harmful ultraviolet radiation.

Visibility: The characteristic of an indication that enables theobserver to see it against the conditions of background,outside light, etc.

Viscosity: The state or degree of being viscous. The resistance of afluid to the motion of its particles.

Visible dye penetrant: A testing penetrant that is characterized by its intensevisible colour usually red. Also called colour contrast ornon-fluorescent penetrant.


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Wash: See Rinse.Water soluble developer: A developer in which the developer powder is dissolved in

a water carrier to form a solution. Not a suspension.Water suspendable developer: A developer in which the developer particles are mixed

with water to form a suspension.Water wash: A penetrant removal technique wherein excess penetrant

is washed or flushed from the test surface with water.Water washable penetrant: A type of penetrant that contains its own emulsifier,

making it water washable.Water tolerance: The amount of water that a penetrant, emulsifier can

absorb before its effectiveness is impaired.Wet developer: A developer in which the developer powder is applied as a

suspension or solution in a liquid usually water oralcohol.

Wettability: The ability of a liquid to spread out spontaneously andadhere to solid surfaces.

CONVERSION TABLE1 m 1 000 mm 1 000 000 m 1 000 000 000 nm1 Bar 14.5 Psi 100 000 Pascal3650 365 nm10 W/m 1 000 w/cm

1 fc (foot-candle) 10,76 lx (lux)1 C (? F - 32) x 5/9


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CHAPTER 3 VISIBLE METHODS

Visible penetrant testing materials were specially designed to be easier and more portable fordoing remote testing with less requirements for lighting and viewing conditions. However, eachstep in the process has to be specifically selected for each component, its location, practicalityand type of discontinuities sought. Flow charts of the visible processes are shown later withdescriptions and possibilities of each step to follow.

PRE-REQUISITES FOR INSPECTIONSelection of the suitable penetrant type and process for a particular test depends on thesensitivity required, number of parts to be tested, surface condition of the parts, geometry ofparts to be tested, availability of resources (electricity, water, compressed air) and area of test.The advantages and disadvantages are set apart as follows for each type of visible process.VISIBLE WATER WASHABLE PROCESS:Advantages

Easily washed with water Good for quantities of small specimens Good for use on rough surfaces Good for use on keyways and threads Fast, single step process Relatively inexpensive

Disadvantages Not reliable for fine, shallow or broad discontinuities Easily over washed Penetrant easily contaminated with water

Watersolubledeveloper

Wash offwith water

WatersuspendibleDeveloper

NonAqueouswetdeveloper

VisibleWaterWashablePenetrant


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VISIBLE SOLVENT REMOVABLE PROCESS:Advantages

Portability No water required Good on anodized specimens Good for spot checking

Disadvantages Flammable materials Removal of excess surface penetrant is time consuming Materials not recommended to be used in open tanks Difficult to use on rough surfaces such as cast components Health hazard in enclosed spaces

VISIBLE POST EMULSIFICATION PROCESSAdvantages

High sensitivity for very thin discontinuities such as tight cracks Easily washed with water after emulsification Good on wide shallow discontinuities Short penetration time Cannot be easily over-washed

Disadvantages Two step process Equipment required for emulsifier application Difficult to remove penetrant from threads, keyways, blind holes, rough surfaces, etc. More expensive

VisibleSolventRemovablePenetrant


Wipe withsolventdampenedcloth

Postemulsifier



Hydrophilic(waterbased)


Lipophilic(oil based)

Wash withwater


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PRE-CLEANINGChoosing the correct pre-cleaning material is an essential step in the penetrant process. No singlecleaning method is appropriate for all metals or contaminants. The pre-cleaning method must becapable of removing dirt and oils without causing harm to the article under inspection. Certainelements such as sulfur and chlorine have detrimental effects on certain materials such as Nickelalloys, certain Stainless Steels and Titanium which could structurally damage the material. Thesurface and all openings of discontinuities must be thoroughly cleaned to ensure that allcontaminants (oil, water, oxides, paint, dirt, grease, lint, mould material, weld spatter, flux, etc.)that may prohibit or restrict the penetrant from entering the discontinuities, are completelyremoved. All cleaning materials used should be compatible with other penetrant materials to beused. Since the compatibility is not always a sure thing, general practice recommends the part tobe flushed with an approved solvent from the same family of penetrant materials to be used andwiped with a clean dry cloth/ paper towel (lint-free) prior to testing. Typical cleaners wouldinclude:SOLVENT CLEANINGSolvent cleaning may use tanks for immersion, or the solvent material may be sprayed, brushedor wiped on and wiped off. Solvent cleaning is the process most commonly used for spotinspections. However environmental, health and safety concerns are making detergent cleaningand steam cleaning more attractive options. A solvent cleaner must evaporate readily andcompletely from the surface and from the surface connected to the discontinuities. Solventcleaners should only be used to remove organic contaminants such as oil, grease, dirt, lint, etc.

DETERGENT CLEANINGImmersion tanks or and detergent solutions are common means of accomplishing the cleaningrequired by liquid penetrant tests. The detergents wet, penetrate, emulsify and saponify (changeto soap) various soils. The only special equipment requirement imposed by penetrant testcleaning is the need for suitable rinsing and drying facilities. When thoroughly rinsed and dried,detergent cleaning leaves a test surface that is physically and chemically clean. Detergentcleaners should have a combination of detergency (cleaning} dispersion, emulsifying, foaming,solubilizing and wetting properties.

VAPOR DEGREASINGIn a vapour degreaser, solvent is boiled at the bottom of a deep tank. The parts are lowered intothe vapors but not into the boiling liquids. Vapor degreasing is probably the most effective in theremoval of oil, grease and similar organic contamination. However, there are restrictions as to itsuse before and after liquid penetrant testing. Safety and environmental concerns have virtuallyeliminated vapor degreasing. Degreasing must be limited to those material that have beenapproved for this method of cleaning. Unlike water based cleaners, vapour degreasing does notrequire a rinse step or a drying (oven) step.

STEAM CLEANINGSteam cleaning equipment is particularly adaptable to the cleaning of large, unwieldy test objectsnot easily cleaned by immersion. Special equipment is required for steam cleaning of test objectsdestined for liquid penetrant testing. Steam with alkaline detergent emulsifies, softens ordissolves the organic contaminant, and the steam gives the mechanical action to remove alkalinedetergent/contaminant from the test object.


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ULTRASONIC CLEANINGUltrasonic agitation is often combined with solvent, detergent or alkaline cleaning to improveefficiency and reduce cleaning time. Ultrasonic cleaning equipment is useful in the cleaning oflarge quantities of small test objects. In many cases, special approvals must be granted to useultrasonic agitation.

CHEMICAL CLEANINGEnsure that chemicals are compatible with materials under test and that manufacturersrecommendations are followed at all times. Be aware that acids are not allowed to dwell on theparts too long so an enormous loss of material is present. Paint strippers may be used to removeall coatings from the material. Rust and surface scale removers are used to remove an excess ofcontaminants when physical removal is prohibited. Test objects that had metal smearingoperations often require etching to prepare them for liquid penetrant testing. This process usesan acid or alkaline solution to open and remove smeared metal from surface discontinuities. Allacid or alkaline residues must be neutralized and removed before liquid penetrant testing. Theetching and neutralizing processes use either tanks for immersion or manual equipment andmaterials.

PRECLEANING PROCESSES TO BE AVOIDEDBlast (shot, sand, grits or pressure), liquid honing, emery cloth, grinders, power wire brushes andmetal scrapers should not be used on the test object before liquid penetrant testing. Theseprocesses tend to close discontinuities by smearing metal, peening or cold working the surface. Ahand wire brush may be helpful in removing rust, surface scale or paint. Relatively fine bristlebrushes should be used and light pressure exerted to prevent smearing of softer metals.

DRYING PRIOR TO PENETRANT APPLICATIONIt is very important to ensure all surfaces and all potential discontinuities are completely dry priorto the application and dwell of penetrant. If any liquid pre-cleaner remains in discontinuities, thepenetrant may be unable to enter discontinuities and an inadequate exam will be performed.This is critical because the technician may not be aware that penetrant did not enter thediscontinuities. Drying of the part or surface should be determined by the area where work isperformed, ambient temperature and air ventilation. Some specifications require the use of ovendryers that help with the evaporation of the pre-cleaners from the part.

PENETRANT APPLICATIONThe application of penetrant is performed after the test surface is completely clean and has beenproperly dried. Almost any method is allowed for penetrant application including spraying,brushing, pouring or dipping. Penetrant should never be allowed to dry completely on the testsurface. The test object must be turned or moved to prevent pooling of penetrant during thedwell time. It is important that all test surfaces are completely wetted with a thin coat ofpenetrant for the entire specified dwell time.


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PENETRANT DWELL TIMEThe penetrant dwell time is the length of time that the penetrant is allowed to wet the surfaceand soak into discontinuities. Some specifications and company procedures require differentpenetrant dwell times for different types of materials or discontinuities. These times will bespecifically required for the particular test object or procedure referenced. Dwell times varybetween 5 and 60 minutes depending upon the manufacturers recommendations, temperature,material, size and type of the discontinuity sought, which is the primary factor.

REMOVAL OF EXCESS PENETRANTSOLVENT WIPE METHODAfter the required penetrant dwell time, the test object is first wiped with a clean, dry, lint freecloth or paper towel. The towel should be white, or a colour that contrasts with the penetrant.The removal of the bulk excess penetrant works best if clean sections of cloth are used for eachwipe. After the bulk of the excess penetrant is removed with dry cloths, the remaining penetrantis removed with solvent dampened cloths. In no case should the cloths be saturated with cleaner.If any cleaner drips or can be squeezed from the cloth, it is too wet and may remove thepenetrant from shallow discontinuities completely. When the surface of the test object is visuallyfree from penetrant and the wipe cloth is relatively clean after each wipe, the manual wipingprocess is complete.

POST EMULSIFICATION HYDROPHILIC (WATER BASED)The test object is ready for emulsification after the proper oil base penetrant is applied and thedwell time has elapsed. The hydrophilic emulsifier and water can be used to remove the oil basedpenetrant. Hydrophilic emulsifier is water based and is supplied in a concentrated form that isdiluted in water concentrations of 10 to 30% for dip applications, and 0.05 to 5% for sprayapplications. A water pre-rinse is required to help remove some of the bulk penetrant beforedipping in the emulsifier. This helps prevent some of the penetrant contamination in theemulsifier tank. Hydrophilic emulsifier acts on the penetrant from the surface by detergentaction. The spray or agitation in the tank provides a scrubbing action. The emulsification time fordip tank applications is determined by experimentation and is normally 120 s maximum. Themanufacturer will specify the proper concentration of emulsifier in water, which should bechecked periodically with a refractometer. Tanks of emulsifier will mix with a small amount ofpenetrant during the dipping process over a period of time. This is one reason for periodic checksto monitor the system materials and performance.

POST EMULSIFICATION LIPOPHILIC (OIL BASED)After the proper oil based penetrant is applied and the dwell time has elapsed, the test object isready for emulsification. The Lipophilic emulsifier is typically located in a dip tank, and is acontrasting colour from the penetrant so that it forms a visible coat over the penetrant to ensurecomplete coverage. Application is typically by dipping, but flowing may be used. No agitation ofthe test object is allowed. The Lipophilic emulsifier acts by diffusing into the oil base penetrantand scraping the penetrant from the surface, making it water washable. The emulsification timeis determined by experimentation and depends on the features of the test object, the uniformdipping and draining of the test object and the viscosity of the emulsifier. This makes uniformdipping, draining and emulsification time very important, so this method is typically monitored in


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seconds. The maximum time allowed is 180 s for fluorescent systems and 30 s for visible systems,and will be shorter for smoother test objects. After the proper emulsification, the water rinse isidentical to the water wash method.

WATER WASH METHODAfter the required penetrant dwell time and proper emulsification (if applicable), the water rinseshould be coarse droplets normally applied in an oblique angle (45 to 70) from a distance ofabout 30 cm. The standard nozzles available from approved non-destructive testing suppliershave been qualified for standard industry techniques. The water pressure should be controlledand not exceeding the requirements set out in the referenced code section according to yourprocedure/ application. The rinse is typically accomplished at a rinse station with adequate lightconditions. The light should shine on the test object so that the technician can evaluate when theexcess penetrant is removed. The technician should also ensure there is no over washing. Whenthe excess surface penetrant is removed, the surface water is drained or removed from thecavities, holes or pockets. If allowed by the procedure, blotting or even filtered air spray may beused, but care should be used not to smear any indications that may begin to bleed out.

DRYING AFTER EXCESS PENETRANT REMOVALThe drying of a part after excess penetrant has been removed depend upon the type ofdeveloper used. This is preferably carried out in a thermostatically controlled air circulating oven,but, drying by normal evaporation is permitted if the procedure is authorized. Somespecifications may stipulate a low drying temperature in order to further control the penetrantevaporation. The period of drying should be the minimum required to achieve the purpose andshould be established for each particular job, taking into consideration its size, shape and also thenature of suspected discontinuities. Excessive drying may cause a reduction in the colourbrilliance of the penetrant bleed-out. Drying of the part is crucial before the application ofSolvent based developer, especially when penetrant was cleaned off with the water washmethod and post-emulsification method. If it is intended to use water suspendible or watersoluble developers, the developer is applied immediately after the excess penetrant has beenremoved, whilst the surface is still wet and before surface drying is carried out. Drying thenassists in securing a uniform developer coating.

DEVELOPER APPLICATIONAll developers must be applied so that a thin uniform coating covers the entire test surface.Application of an excessive thickness can obscure, cover or extinguish indications. The developerassists in the detection of penetrant retained in the discontinuities by aiding in the bleed-outprocess by acting as a blotting agent.

DRY POWDER DEVELOPERNot allowed for use with the visible methods.


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WATER SOLUBLE DEVELOPERWater soluble powder crystals are mixed with water and dissolve in the solution, following themanufacturers recommendations. The developer solution mixture concentration is verified bychecking the specific gravity of the liquid with a hydrometer after mixing. Water solubledeveloper concentration will change over time due to evaporation losses. Therefore, thedeveloper concentration should be checked on a weekly basis. The application occursimmediately following excess penetrant removal and/or emulsification from the test object andafter draining or shaking off excess water, but before drying time. Wet developer is applied bydipping (immersion), flow or spray techniques. Immersion in a prepared tank of developer is themost common application method. With immersion testing, the test object is immersed only longenough to coat all surfaces. It should then be removed immediately, and all excess from recessesor trapped areas should be drained to prevent pooling of developer, which can obscureindications. Wet developer is applied to form a smooth, even coating. Particular care should betaken to avoid concentrations of developer in dished or hollowed areas of the test object. Suchconcentrations of developer may mask penetrant indications and are to be avoided. Thisdeveloper is not normally used for critical applications or on complex geometry test objects.

WATER SUSPENDIBLE DEVELOPERWater suspendable developer is a suspension of white powder mixed with water, following themanufacturers recommendations. Water suspendable developers require constant mildagitation (or thorough agitation before and during use) to keep the powder particles insuspension. The water suspendable mixture concentration is verified by checking the specificgravity with a hydrometer after mixing. Water suspendable developer concentration will changeover time due to evaporation losses. Therefore, the developer concentration should be checkedon a weekly basis. The application immediately follows excess penetrant removal from the testobject and after draining or shaking off excess water, but before drying time. The wet developeris applied by dipping (immersion), flow or spray techniques. Immersion in a prepared tank ofdeveloper is the most common application method. The test object should be immersed onlylong enough to coat all surfaces. It should then be removed immediately, and all excess fromrecesses or trapped areas should be drained to prevent pooling of developer, which can obscureindications. Wet developer is applied to form a smooth, even coating. The fact that constantagitation is required to maintain the proper mixture concentration is a disadvantage of watersuspendable developers. Care should be taken not to generate foam during agitations becausefoam will cause uneven surface coating. This developer is not normally used for criticalapplications or on complex geometry test objects.

NON AQUEOUS WET DEVELOPERNon-aqueous wet developer is a powder suspended in a volatile liquid solvent. The volatile liquidgives the advantage of decreasing the viscosity and increasing the liquid bulk in the cavity. Thisaction forces the penetrant to surface where it assist the dispersion of the penetrant away fromthe discontinuity. The evaporation of the solvent tends to pull penetrant into the developer.Non-aqueous wet developer is the most sensitive developer. The application is by spraying, andthe volatile liquid evaporates rapidly so that no delayed drying operation is required. The spray oraerosol container must be thoroughly agitated just before spraying, and spraying should be donesparingly so that a thin coating covers the entire test area. The sheen of the metal should barelybe covered. Several light coats are usually preferable, rather than attempting to cover the testarea with one spray. A light check spray should be performed away from the test surface toensure the spray nozzle is clean and free of obstructions.


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DEVELOPER DWELL TIMEThis is the time allowed between the application of developer and the actual final viewing ofindications. It is very important in the interpretation of indications because if too little time isallowed, indications may not have had time to develop. Too much time will cause the indicationsto become blurred or distorted. Developer dwell times vary with specification, companyprocedures or techniques, type of materials, type of discontinuity to be detected, and type ofdeveloper to be used. These dwell times typically range between 5 min and 4 hrs.

VIEWING CONDITIONSWhether or not an indication will be seen involves the relative amount of light reflected which inturn, should provide a clear difference between an indication and its background. The intensity oflight should be measured at the surface of the inspected part and in some cases even theambient light should be tested. In visible methods we have to ensure that enough visible light(white light) is available. Visible light intensities are measured in units of lux or foot-candles.These intensity values are specified by the referencing code in the procedure to be used.

INTERPRETATIONTo interpret an indication is to decide what condition caused it. The technician should firstdetermine if the indication is false, non-relevant or relevant. One method of determining if anindication is relevant is to dampen a cotton swab with solvent and gently wipe the indication off.If the indication reappears, it is a relevant indication. This technique is known as the bleed backmethod. If the indication is found to be non-relevant, the technician must determine the sourceof the invalid indication and correct the problem. Test objects with false indications must be re-cleaned and reprocessed.

FALSE INDICATIONSThe most common sources of false indications is poor cleaning of test objects, poor removal ofexcess penetrant, penetrant on the hands of the technician, contamination of developer (doesnot apply to aerosol cans), penetrant rubbing off from one object to another and penetrant spotson testing table. These indications cannot be ignored as they may mask relevant indications.Therefore, re-processing shall be done.

NON-RELEVANT INDICATIONSNon-relevant indications are caused by features in the test object that are there by design, butare in no way a relevant discontinuity. Non-relevant indications include those that appear on testobjects that are press fitted, riveted or spot welded together, and those caused by surfaceroughness. Any non-relevant indication that interferes or could mask a relevant indication mustbe further evaluated and sometimes retested. If a test object is too rough to perform a properliquid penetrant test, or has a condition like weld undercut that has been accepted visually, thetest object or weld may have to be returned for further preparation for liquid penetrant testing.


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RELEVANT INDICATIONSRelevant indications are those caused by a material discontinuity. The interpretation of anindication as relevant is a matter of observing the indication, eliminating the possibility of it beinga false indication and then further determining that it is not a non-relevant indication. Anyrelevant indication immediately becomes subject to evaluation of its cause (type ofdiscontinuity). Some procedures allow measuring the visible discontinuity size after wiping outthe developer, other procedures require evaluation to be done considering the entire size of theindication bleed-out. When the technician determines that the indication is relevant, it must thenbe evaluated to the acceptance criteria.

POST CLEANINGPenetrant inspection residues can have several adverse effects on subsequent processing andservice. Developer and penetrant residues left on the test part, have detrimental effects on theapplication of surface finishes such a painting, plating, and anodizing. Penetrant residues left inthe discontinuities can seriously affect the weld quality if not removed prior to repair welding.Developer residues can interfere with the functioning of the part if they involve a moving or wearsurface. In addition, developer materials can absorb and retain moisture resulting in corrosion ofthe part. Except for liquid oxygen, food compatibility and the chlorine/ sulfur free requirementsin the pre-cleaning and post-cleaning of nickel alloys, certain stainless steels and titanium, nospecial materials are required for post cleaning unless required by specification of companyprocedures.

REPORTINGA detailed report should be made in accordance with the clients requirements, procedure for theinspection and referencing code specifications. These reports must be easily understandable andclear. Each report has its own number and must be signed off by an approved level II or level IIItechnician for it to be valid. A report would generally consist of information on the method oftest, part specifications/ identification, penetrant material identifications, penetrant methodsand techniques. The report is normally accompanied by photos and/ or drawings on the findingswith results of the interpretation and evaluation made by technician.


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CHAPTER 4 FLUORESCENT METHODS

Fluorescent penetrant testing materials were specially designed to be more sensitive to finediscontinuities and indications to be more visible and easier to detect. However, each step in theprocess has to be specifically selected for each component, its location, practicality and type ofdiscontinuities sought. The fluorescent methods require special purpose light sources andviewing conditions that might be found more expensive and is found to be less portable than thevisible methods. Contamination of the materials is a higher risk and high temperatures couldquench the fluorescence of the penetrants. Fluorescent testing can never be performed on asurface after visible penetrant tests since the fluorescent brilliance of the penetrant may bediminished by the residual visible penetrants in the discontinuities. Technicians may need to takebreaks from viewing to regain the concentration as special viewing conditions and ambientlighting could restrain the eyesight. Flow charts of the fluorescent processes are shown later withdescriptions and possibilities of each step to follow.

PRE-REQUISITES FOR INSPECTIONSelection of the suitable penetrant type and process for a particular test depends on thesensitivity required, number of parts to be tested, surface condition of the parts, geometry ofparts to be tested, availability of resources (electricity, water, compressed air) and area of test.The advantages and disadvantages are set apart as follows for each type of visible process.

FLUORESCENT SOLVENT REMOVABLE PROCESS:Advantages

Very high sensitivity No water required Good on anodized specimens Good for spot checking

Disadvantages Flammable materials Removal of excess surface penetrant is time consuming Materials not recommended to be used in open tanks Difficult to use on rough surfaces such as cast components Health hazard in enclosed spaces Overly sensitive if cleaning is not properly done Difficult to remove penetrant from threads, keyways, blind holes, rough surfaces, etc.


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FLUORESCENT POST EMULSIFICATION PROCESSAdvantages

High sensitivity for very thin discontinuities such as tight cracks Easily washed with water after emulsification Good on wide shallow discontinuities Short penetration time Cannot be easily over-washed

Disadvantages Penetrant may be contaminated with water and fluorescence reduced Two step process Equipment required for emulsifier application Difficult to remove penetrant from threads, keyways, blind holes, rough surfaces, etc. More expensive

FluorescentSolventRemovablePenetrant


Wipe withsolventdampenedcloth

Postemulsifier


Drydeveloper

Hydrophilic(waterbased)

Drydeveloper

Lipophilic(oil based)

Wash withwater




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FLUORESCENT WATER WASHABLE PROCESS:Advantages

Easily washed with water Good for quantities of small specimens Good for use on rough surfaces Good for use on keyways and threads Fast, single step process Relatively inexpensive

Disadvantages Not reliable for fine, shallow or broad discontinuities Easily over washed Penetrant easily contaminated with water

PRE-CLEANINGChoosing the correct pre-cleaning material is an essential step in the penetrant process. No singlecleaning method is appropriate for all metals or contaminants. The pre-cleaning method must becapable of removing dirt and oils without causing harm to the article under inspection. Certainelements such as sulfur and chlorine have detrimental effects on certain materials such as Nickelalloys, certain Stainless Steels and Titanium which could structurally damage the material. Thesurface and all openings of discontinuities must be thoroughly cleaned to ensure that allcontaminants (oil, water, oxides, paint, dirt, grease, lint, mould material, weld spatter, flux, etc.)that may prohibit or restrict the penetrant from entering the discontinuities, are completelyremoved. All cleaning materials used should be compatible with other penetrant materials to beused. Since the compatibility is not always a sure thing, general practice recommends the part tobe flushed with an approved solvent from the same family of penetrant materials to be used andwiped with a clean dry cloth/ paper towel (lint-free) prior to testing. Typical cleaners wouldinclude:


Wash offwith water


NonAqueouswetdeveloperFluorescent

WaterWashablePenetrant

Drydeveloper


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SOLVENT CLEANINGSolvent cleaning may use tanks for immersion, or the solvent material may be sprayed, brushedor wiped on and wiped off. Solvent cleaning is the process most commonly used for spotinspections. However environmental, health and safety concerns are making detergent cleaningand steam cleaning more attractive options. A solvent cleaner must evaporate readily andcompletely from the surface and from the surface connected to the discontinuities. Solventcleaners should only be used to remove organic contaminants such as oil, grease, dirt, lint, etc.

DETERGENT CLEANINGImmersion tanks or and detergent solutions are common means of accomplishing the cleaningrequired by liquid penetrant tests. The detergents wet, penetrate, emulsify and saponify (changeto soap) various soils. The only special equipment requirement imposed by penetrant testcleaning is the need for suitable rinsing and drying facilities. When thoroughly rinsed and dried,detergent cleaning leaves a test surface that is physically and chemically clean. Detergentcleaners should have a combination of detergency (cleaning} dispersion, emulsifying, foaming,solubilizing and wetting properties.

VAPOR DEGREASINGIn a vapour degreaser, solvent is boiled at the bottom of a deep tank. The parts are lowered intothe vapors but not into the boiling liquids. Vapor degreasing is probably the most effective in theremoval of oil, grease and similar organic contamination. However, there are restrictions as to itsuse before and after liquid penetrant testing. Safety and environmental concerns have virtuallyeliminated vapor degreasing. Degreasing must be limited to those material that have beenapproved for this method of cleaning. Unlike water based cleaners, vapour degreasing does notrequire a rinse step or a drying (oven) step.

STEAM CLEANINGSteam cleaning equipment is particularly adaptable to the cleaning of large, unwieldy test objectsnot easily cleaned by immersion. Special equipment is required for steam cleaning of test objectsdestined for liquid penetrant testing. Steam with alkaline detergent emulsifies, softens ordissolves the organic contaminant, and the steam gives the mechanical action to remove alkalinedetergent/contaminant from the test object.

ULTRASONIC CLEANINGUltrasonic agitation is often combined with solvent, detergent or alkaline cleaning to improveefficiency and reduce cleaning time. Ultrasonic cleaning equipment is useful in the cleaning oflarge quantities of small test objects. In many cases, special approvals must be granted to useultrasonic agitation.

CHEMICAL CLEANINGEnsure that chemicals are compatible with materials under test and that manufacturersrecommendations are followed at all times. Be aware that acids are not allowed to dwell on theparts too long so an enormous loss of material is present. Paint strippers may be used to removeall coatings from the material. Rust and surface scale removers are used to remove an excess ofcontaminants when physical removal is prohibited. Test objects that had metal smearingoperations often require etching to prepare them for liquid penetrant testing. This process usesan acid or alkaline solution to open and remove smeared metal from surface discontinuities. Allacid or alkaline residues must be neutralized and removed before liquid penetrant testing. The


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etching and neutralizing processes use either tanks for immersion or manual equipment andmaterials.

PRECLEANING PROCESSES TO BE AVOIDEDBlast (shot, sand, grits or pressure), liquid honing, emery cloth, grinders, power wire brushes andmetal scrapers should not be used on the test object before liquid penetrant testing. Theseprocesses tend to close discontinuities by smearing metal, peening or cold working the surface. Ahand wire brush may be helpful in removing rust, surface scale or paint. Relatively fine bristlebrushes should be used and light pressure exerted to prevent smearing of softer metals.

CLEANLINESS CHECKIt is crucial to fluorescent testing that the surface to be inspected is checked under an Ultra violetlight after cleaning to ensure that the pre-cleaning was done sufficiently and that nocontaminants that fluoresces can be seen on the material.

DRYING PRIOR TO PENETRANT APPLICATIONIt is very important to ensure all surfaces and all potential discontinuities are completely dry priorto the application and dwell of penetrant. If any liquid pre-cleaner remains in discontinuities, thepenetrant may be unable to enter discontinuities and an inadequate exam will be performed.This is critical because the technician may not be aware that penetrant did not enter thediscontinuities. Drying of the part or surface should be determined by the area where work isperformed, ambient temperature and air ventilation. Some specifications require the use of ovendryers that help with the evaporation of the pre-cleaners from the part.

PENETRANT APPLICATIONThe application of penetrant is performed after the test surface is completely clean, has beenproperly dried and checked under the UV light. Almost any method is allowed for penetrantapplication including spraying, brushing, pouring or dipping. Penetrant should never be allowedto dry completely on the test surface. The test object must be turned or moved to preventpooling of penetrant during the dwell time. It is important that all test surfaces are completelywetted with a thin coat of penetrant for the entire specified dwell time. In fluorescent testing, aUV-light may be used to ensure that the penetrant was applied to the entire area of interest.

PENETRANT DWELL TIMEThe penetrant dwell time is the length of time that the penetrant is allowed to wet the surfaceand soak into discontinuities. Some specifications and company procedures require differentpenetrant dwell times for different types of materials or discontinuities. These times will bespecifically required for the particular test object or procedure referenced. Dwell times varybetween 5 and 60 minutes depending upon the manufacturers recommendations, temperature,material, size and type of the discontinuity sought, which is the primary factor.


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REMOVAL OF EXCESS PENETRANTSOLVENT WIPE METHODAfter the required penetrant dwell time, the test object is first wiped with a clean, dry, lint freecloth or paper towel. The towel should be white, or a colour that contrasts with the penetrant.The removal of the bulk excess penetrant works best if clean sections of cloth are used for eachwipe. After the bulk of the excess penetrant is removed with dry cloths, the remaining penetrantis removed with solvent dampened cloths. In no case should the cloths be saturated with cleaner.If any cleaner drips or can be squeezed from the cloth, it is too wet and may remove thepenetrant from shallow discontinuities completely. When the surface of the test object is visuallyfree from penetrant and the wipe cloth is relatively clean after each wipe, the manual wipingprocess is complete.

POST EMULSIFICATION HYDROPHILIC (WATER BASED)The test object is ready for emulsification after the proper oil base penetrant is applied and thedwell time has elapsed. The hydrophilic emulsifier and water can be used to remove the oil basedpenetrant. Hydrophilic emulsifier is water based and is supplied in a concentrated form that isdiluted in water concentrations of 10 to 30% for dip applications, and 0.05 to 5% for sprayapplications. A water pre-rinse is required to help remove some of the bulk penetrant beforedipping in the emulsifier. This helps prevent some of the penetrant contamination in theemulsifier tank. Hydrophilic emulsifier acts on the penetrant from the surface by detergentaction. The spray or agitation in the tank provides a scrubbing action. The emulsification time fordip tank applications is determined by experimentation and is normally 120 s maximum. Themanufacturer will specify the proper concentration of emulsifier in water, which should bechecked periodically with a refractometer. Tanks of emulsifier will mix with a small amount ofpenetrant during the dipping process over a period of time. This is one reason for periodic checksto monitor the system materials and performance.

POST EMULSIFICATION LIPOPHILIC (OIL BASED)After the proper oil based penetrant is applied and the dwell time has elapsed, the test object isready for emulsification. The Lipophilic emulsifier is typically located in a dip tank, and is acontrasting colour from the penetrant so that it forms a visible coat over the penetrant to ensurecomplete coverage. Application is typically by dipping, but flowing may be used. No agitation ofthe test object is allowed. The Lipophilic emulsifier acts by diffusing into the oil base penetrantand scraping the penetrant from the surface, making it water washable. The emulsification timeis determined by experimentation and depends on the features of the test object, the uniformdipping and draining of the test object and the viscosity of the emulsifier. This makes uniformdipping, draining and emulsification time very important, so this method is typically monitored inseconds. The maximum time allowed is 180 s for fluorescent systems and 30 s for visible systems,and will be shorter for smoother test objects. After the proper emulsification, the water rinse isidentical to the water wash method.


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WATER WASH METHODAfter the required penetrant dwell time and proper emulsification (if applicable), the water rinseshould be coarse droplets normally applied in an oblique angle (45 to 70) from a distance ofabout 30 cm. The standard nozzles available from approved non-destructive testing suppliershave been qualified for standard industry techniques. The water pressure should be controlledand not exceeding the requirements set out in the referenced code section according to yourprocedure/ application. The rinse is typically accomplished at a rinse station with adequate lightconditions. The light should shine on the test object so that the technician can evaluate when theexcess penetrant is removed. The technician should also ensure there is no over washing. Whenthe excess surface penetrant is removed, the surface water is drained or removed from thecavities, holes or pockets. If allowed by the procedure, blotting or even filtered air spray may beused, but care should be used not to smear any indications that may begin to bleed out.

CLEANLINESS CHECKAfter the removal of the excess penetrant from the surface, it is required that the part beinspected under a UV-light to ensure that all penetrant residues have been removed from thesurface. Some specifications require that the cleaning/ washing area is equipped with apermanent UV-light source to check the effectiveness of the cleaning/ wash cycle.

DRYING AFTER EXCESS PENETRANT REMOVALThe drying of a part after excess penetrant has been removed depend upon the type ofdeveloper used. This is preferably carried out in a thermostatically controlled air circulating oven,but, drying by normal evaporation is permitted if the procedure is authorized. Somespecifications may stipulate a low drying temperature in order to further control the penetrantevaporation. The period of drying should be the minimum required to achieve the purpose andshould be established for each particular job, taking into consideration its size, shape and also thenature of suspected discontinuities. Excessive drying may cause a reduction in the colourbrilliance of the penetrant bleed-out. Drying of the part is crucial before the application ofSolvent based developer, especially when penetrant was cleaned off with the water washmethod and post-emulsification method. If it is intended to use water suspendible or watersoluble developers, the developer is applied immediately after the excess penetrant has beenremoved, whilst the surface is still wet and before surface drying is carried out. Drying thenassists in securing a uniform developer coating.

DEVELOPER APPLICATIONAll developers must be applied so that a thin uniform coating covers the entire test surface.Application of an excessive thickness can obscure, cover or extinguish indications. The developerassists in the detection of penetrant retained in the discontinuities by aiding in the bleed-outprocess by acting as a blotting agent.

DRY POWDER DEVELOPERDry developer is loose, fluffy powder used with fluorescent penetrants. After removal of excesspenetrant and/or emulsification and drying, dry powder developer is applied to the test surfacefor the purpose of absorbing penetrant from discontinuities and enhancing the resultant


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penetrant indication. Dry developer may be applied in a dust cloud chamber activated by an airblast. The developer can be applied with an electrostatic sprayer, or the technician can dip thetest object into the dry powder. Excess powder is shaken of the test object. Of the differentdevelopers available, dry developer is the most adaptable to rough surfaces and automaticprocessing. It is also the easiest to handle, apply and remove. Dry powder is not corrosive, givesof no vapors and leaves no residue or film to affect the next processing step. Dry developershould not be used with visible dye penetrant because of the poor contrast provided by the thincoating of very fine powder.

WATER SOLUBLE DEVELOPERWater soluble powder crystals are mixed with water and dissolve in the solution, following themanufacturers recommendations. The developer solution mixture concentration is verified bychecking the specific gravity of the liquid with a hydrometer after mixing. Water solubledeveloper concentration will change over time due to evaporation losses. Therefore, thedeveloper concentration should be checked on a weekly basis. The application occursimmediately following excess penetrant removal and/or emulsification from the test object andafter draining or shaking off excess water, but before drying time. Wet developer is applied bydipping (immersion), flow or spray techniques. Immersion in a prepared tank of developer is themost common application method. With immersion testing, the test object is immersed only longenough to coat all surfaces. It should then be removed immediately, and all excess from recessesor trapped areas should be drained to prevent pooling of developer, which can obscureindications. Wet developer is applied to form a smooth, even coating. Particular care should betaken to avoid concentrations of developer in dished or hollowed areas of the test object. Suchconcentrations of developer may mask penetrant indications and are to be avoided. Thisdeveloper is not normally used for critical applications or on complex geometry test objects.

WATER SUSPENDIBLE DEVELOPERWater suspendable application is a suspension of white powder mixed with water, following themanufacturers recommendations. Water suspendable developers require constant mildagitation (or thorough agitation before and during use) to keep the powder particles insuspension. The water suspendable mixture concentration is verified by checking the specificgravity with a hydrometer after mixing. Water suspendable developer concentration will changeover time due to evaporation losses. Therefore, the developer concentration should be checkedon a weekly basis. The application immediately follows excess penetrant removal from the testobject and after draining or shaking off excess water, but before drying time. The wet developeris applied by dipping (immersion), flow or spray techniques. Immersion in a prepared tank ofdeveloper is the most common application method. The test object should be immersed onlylong enough to coat all surfaces. It should then be removed immediately, and all excess fromrecesses or trapped areas should be drained to prevent pooling of developer, which can obscureindications. Wet developer is applied to form a smooth, even coating. Particular care should betaken to avoid concentrations of developer in dished or hollowed areas of the test object. Suchconcentrations of developer may mask penetrant indications and should be avoided. The factthat constant agitation is required to maintain the proper mixture concentration is adisadvantage of water suspendable developers. Care should be taken not to generate foamduring agitations because foam will cause uneven surface coating. This developer is not normallyused for critical applications or on complex geometry test objects.


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NON AQUEOUS WET DEVELOPERNon-aqueous wet developer is a powder suspended in a volatile liquid solvent. The volatile liquidgives the advantage of decreasing the viscosity and increasing the liquid bulk in the cavity. Thisaction forces the penetrant to surface where it assist the dispersion of the penetrant away fromthe discontinuity. The evaporation of the solvent tends to pull penetrant into the developer.Non-aqueous wet developer is the most sensitive developer. The application is by spraying, andthe volatile liquid evaporates rapidly so that no delayed drying operation is required. The spray oraerosol container must be thoroughly agitated just before spraying, and spraying should be donesparingly so that a thin coating covers the entire test area. The sheen of the metal should barelybe covered. Several light coats are usually preferable, rather than attempting to cover the testarea with one spray. A light check spray should be performed away from the test surface toensure the spray nozzle is clean and free of obstructions.

DEVELOPER DWELL TIMEThis is the time allowed between the application of developer and the actual final viewing ofindications. It is very important in the interpretation of indications because if too little time isallowed, indications may not have had time to develop. Too much time will cause the indicationsto become blurred or distorted. Developer dwell times vary with specification, companyprocedures or techniques, type of materials, type of discontinuity to be detected, and type ofdeveloper to be used. These dwell times typically range between 5 min and 4 hrs.

VIEWING CONDITIONSWhether or not an indication will be seen involves the relative amount of light reflected which inturn, should provide a clear difference between an indication and its background. The intensity oflight should be measured at the surface of the inspected part and in fluorescent testingapplications even the ambient light should be tested. In fluorescent methods we have to ensurethat only a certain amount of visible light (white light) is present in the area. Visible lightintensities are measured in units of lux or foot-candles. The Ultra Violet light source should bemeasured at the surface and has to achieve a specified minimum intensity. UV-light is measuredin units of W/cm2. These intensity values are specified by the referencing code in the procedureto be used.

INTERPRETATIONTo interpret an indication is to decide what condition caused it. The technician should firstdetermine if the indication is false, non-relevant or relevant. One method of determining if anindication is relevant is to dampen a cotton swab with solvent and gently wipe the indication off.If the indication reappears, it is a relevant indication. This technique is known as the bleed backmethod. If the indication is found to be non-relevant, the technician must determine the sourceof the invalid indication and correct the problem. Test objects with false indications must be re-cleaned and reprocessed.


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FALSE INDICATIONSThe most common sources of false indications is poor cleaning of test objects, poor removal ofexcess penetrant, penetrant on the hands of the technician, contamination of developer (doesnot apply to aerosol cans), penetrant rubbing off from one object to another and penetrant spotson testing table. These indications cannot be ignored as they may mask relevant indications.Therefore, re-processing shall be done.

NON-RELEVANT INDICATIONSNon-relevant indications are caused by features in the test object that are there by design, butare in no way a relevant discontinuity. Non-relevant indications include those that appear on testobjects that are press fitted, riveted or spot welded together, and those caused by surfaceroughness. Any non-relevant indication that interferes or could mask a relevant indication mustbe further evaluated and sometimes retested. If a test object is too rough to perform a properliquid penetrant test, or has a condition like weld undercut that has been accepted visually, thetest object or weld may have to be returned for further preparation for liquid penetrant testing.

RELEVANT INDICATIONSRelevant indications are those caused by a material discontinuity. The interpretation of anindication as relevant is a matter of observing the indication, eliminating the possibility of it beinga false indication and then further determining that it is not a non-relevant indication. Anyrelevant indication immediately becomes subject to evaluation of its cause (type ofdiscontinuity). Some procedures allow measuring the visible discontinuity size after wiping outthe developer, other procedures require evaluation to be done considering the entire size of theindication bleed-out. When the technician determines that the indication is relevant, it must thenbe evaluated to the acceptance criteria.

POST CLEANINGPenetrant inspection residues can have several adverse effects on subsequent

3001 Rev.0 - Liquid Penetrant Testing Level 1 & 2 Combined - Note Book

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