Liquid Penetrant Testing 2

Liquid Penetrant Testing :Discontinuities are detected by a penetrating colored liquid.Indications form directly over the defect. This method detects surface breaking discontinuities only.

• This examination process is useful for detection of open to surface discontinuities only.• Applicable to varieties of non porous materials.• Produces enlarged indication for easy detection.• Relative volume of a flaw is indicated by the amount of bleed out.

Testing Limitations :• This process requires elaborate surface cleaning.• Surface cleaning shall be properly done otherwise there will not show any indication.• Processing is time consuming.• The process has temperature limitations. 100 to 520 C. [ 2000 C, if high temp special penetrant materials are used ].• requires careful processing.• Does not indicate the size of the discontinuities.• Difficult to test porous materials & rough surface.• Requires post cleaning.

Penetrant Process : Step 1Surface is cleaned to remove all contaminants to the extent that the interior of the discontinuities are clean and dry.

• Surface to be cleaned using appropriate cleaning methods such that dirt, oil, grease, scale, rust, paint etc are completely removed.• The flaw openings must be clean to allow entry of penetrant. • Following cleaning, the part shall be completely dried.

Penetrant Process : Step 2penetrant may be applied by, spraying, dipping, flooding, brushing.

• For penetrant application the part temperature must be within 100 to 500 C.• Penetrant must be applied to clean dry surface.• The entire area to be tested must be covered with a thin layer of penetrant.• Penetrant must not dry during the entire test cycle.• A penetration time between 10 to 30 minutes are used.

Penetrant Process : Step 3To detect entrapped penetrant, excess penetrant on the surface is removed. Care must be taken not to remove entrapped penetrant from the discontinuities.

• Depending on the type of penetrant, excess surface penetrant is removed by one of the following methods,• Rinsing with coarse water spray.• Emulsifying the penetrant and rinsing with water spray.• Rinsing with emulsifier solution.• Manually wiping the surface with solvent dampened cloth.

Penetrant Process : Step 4A Developer is applied to bring entrapped penetrant back to the surface by reverse capillary action [ blotting ].

• A developer, uniform coating of fine white powder, is used for blotting the penetrant out of the discontinuities.• Developer also provides a contrasting background for the indication.• Penetrant bleeds and spreads into developer and the indication become easily detectable. The indication may enlarge with time.

Penetrant test method :The pre cleaning operation removes surface contaminants and opens up the discontinuities.

Penetrant test method :

Portable kit for Penetrant testing :For field use penetrant materials are packed in aerosol spray cans.A set of cleaner / remover, penetrant and developer are all that required to carry out the field examination.Aerosol cans provide uncontaminated liquids for the examination and can have a shelf life of 5 years. However, if the pressure inside the can drops significantly, the can becomes useless.

Penetrant materials are available in aerosol spray cans as well as in bulks.

Surface Cleaning :Very important step in penetrant testing.Cleaning must clear the discontinuity opening to allow the penetrating liquid to enter.

Surface contaminations closes Discontinuity openings :Surface cleaning plays critical role for effective penetrant testing

• Any contamination such as oil, rust, scale, corrosion & different types of coatings and surface treatments cover the discontinuity opening and prevent entry of penetrant in to it.• To detect the discontinuities, test surface shall be free from abovementioned contaminations, otherwise indications will not appear.

Contaminants does not allow penetrant to enter discontinuities

• Dirt and contamination blocks or closes the discontinuity openings and prevent entry of penetrant.• If a discontinuity is filled, there is no room for the penetranrt to enter.• This is a limitation of liquid penetrant testing where as magnetic particle testing can be carried out even with foreign material embedded onto the discontinuities.

Parts shall be cleaned such that the interior of the discontinuities are free from contaminants and dry :

Cleaning Methods :• Detergents.• Steam cleaning for assemblies• Solvents for oil, grease etc• Hot Alkaline cleaning• Ultrasonic agitation with cleaning materials. • Paint strippers • Acid or alkaline etching for rust scales and corrosion.

Parts shall be cleaned such that the interior of the discontinuities are free from contaminants and dry :

Cross section of a part shows entrapped penetrant :

• The liquid must fill the cavity as much as possible. This depends on the viscosity of the penetrant and the temperature of the part.• At higher temperature, the liquid has low viscosity and enters and fill a cavity easily.• At low temperature the viscosity increases and longer penetration time is needed.

Capillary action forces liquid into narrow openings :Color contrast penetrant entered a crack.

Dirty part surface requires cleaning : Rust and rough surfaces requires cleaning.

Rust and corrosion on test surface requires cleaning :

Paint closes and fills discontinuity openings and blocks the passage of penetrant entry. All traces of paint must be removed.

A pair of Gears before cleaning :

The Gears after cleaning :

Light deposits of oil and grease on the part can be removed by solvent cleaner supplied with the spraying kit.

A large number of small parts can be cleaned together for penetrant examination :

before cleaning after cleaning

Parts shall be cleaned such that all contaminants are removed :

Parts shall be cleaned such that all contaminants are removed :

before cleaning after cleaning

Parts being cleaned by detergent washing :

Parts to be cleaned by solvent removers :

Remover cleans oily deposits :

Appearance of part surface after cleaning :

Solvent spray cleaning :

Solvent dip cleaning :

Removing paint with solvent wipe.

Removing paint with solvent.

Removing paint stripper

Removing rust

Removing paint stripper

Removing rust with solution.

Etching

Compact machine cleaning unit with part basket.

Grid and basket inside the compact cleaning unit :

Large and heavy part cleaning tank :

Agitation of cleaning liquid in the cleaning tank :

Agitated [Turbulent] water speed up cleaning :

Degreasing unit :for removing oily deposits from used parts.

Remover agitation accelerates Degreasing :

Remover agitation used for Degreasing :

Cleaning line :

Ultrasonic cleaning : is highly effective in cleaning the interior of discontinuities and residual penetrant after examination.This method takes advantage of ultrasonic agitation with suitable cleaning agents.The ultrasonic agitation makes microscopic bubbles.

Ultrasonic agitation produces microscopic bubbles which explodes and displaces surrounding material. It may take 30 to 60 minutes for complete cleaning.

An Ultrasonic cleaning unit with power supply.

Ultrasonic units are available in different sizes. Different types of cleaning agents to be used with, are also supplied :

Parts cleaned by ultrasonic method :

If water is used as the cleaning medium, the parts must be thoroughly dried before penetrant application.

Grid and hot airflow ducts in the drying cabinet :

Drying is achieved by circulating hot air through ducts inside the dryer.

Hot air dryer Dryer with Basket for part handling :

Drying parts in a vacuum dryer : Water boils at 50 C when the pressure is very low. A vacuum dryer is most efficient for quick drying of parts at lower temperature.Pressure is lowered in a vacuum dryer such that water boils at 400 C. Parts become dry in 10 minutes at 400C, which is ideal for direct penetrant application. A medium size part or a number of small parts can be dried in the vacuum oven.

Part surface after cleaning and drying.

Peening

Part surface after cleaning and drying.

Part surface cleaned and dried.

Part cleaned for penetrant application :

cleaned part showing crack opening.

Penetrant sprayed on the part . The surface excess penetrant have to be removed after the dwell time. Then a developer can be applied to complete the process.

Appearance of a defect free part after developer application.

Penetrant indication of the defect in the part after developer application.

Capillary Action : Principle of Liquid penetrant testing.

Liquid enters narrow openings due to capillary action.

• Liquid rises through the cavity of a fine bore tube against the gravity. This is known as capillary action.• The finer the bore, the more is the capillary force.• Liquid enters narrow discontinuities because of capillary forces. • A plant takes in water through capillary action.

Contact Angle :A good penetrant must easily spread on the test surface and enter tight discontinuity openings.

• Low surface tension and low contact angle allow liquids to spread on the surface easily.• Liquid penetrants are formulated to have low surface tension, low contact angle and low viscosity.• Higher viscosity reduces the speed of penetration.

Types of Penetrants :

Liquid penetrants are available in three types.

Type 1 : Fluorescent dye, visible only under Ultra Violet light.

Type 2 : Color contrast, visible in ordinary light, usually Red color.

Type 3 : Dual sensitivity. Combination of fluorescent and color dye. Examined under ultra violet as well as ordinary light. Used for special applications.

Penetrant is a solution of brightly colored visible or fluorescent dye in a colorless non volatile liquid, usually highly refined hydrocarbon distillates. The penetrant possesses many controlled properties for its successful operation.

Visible dye used in the penetrant is bright red or magenta in color. Fluorescent dye is a pale yellow liquid which fluoresces brilliant yellow-green in color under ultraviolet illumination.

Fluorescent indication Color contrast indication

Fluorescent Type 1 : These penetrants contain a fluorescent dye and are visible only under ultraviolet illumination in a darkened area. The penetrants have high sensitivity and used for sensitive applications.

Color contrast Type 2 : These penetrants use a color dye visible under ordinary light. The penetrants have lower sensitivity compared to fluorescent types and is used when high sensitivity is not required.

Color contrast Process :

These penetrants use a brightly colored red dye visible under ordinary light.

These penetrants are recommended ;

when the part can not be inspected in a darkened area

when electrical supply is not available.

When high sensitivity is not required.

Fluorescent Process :

These penetrants contain a fluorescent dye and are visible only under ultraviolet illumination in a darkened area. These penetrants have high sensitivity and used for high sensitivity examinations. Fluorescent penetrants are available in five different sensitivity levels [ ½ to 4 ].The use of minimum sensitivity penetrant which is capable of detecting the discontinuities of interest is recommended.

Pentrant materials are oftened packed in aerosol cans. The materials are also available in bulk containers.

Penetrant application :

* Before penetrant application part surface must be thoroughly cleaned and dried.

* The penetrant must cover the examination area in a thin consistent layer.

* Penetrant may be applied by dipping, spraying, flooding or brushing.

* Application by rubbing with a penetrant soaked cloth is not permitted.

Penetrant application by a brush :For testing of a small area, penetrant may be applied with a brush.

Application of penetrant by brushing is also preferred in a confined area where fine spray floating in the air is hazardous to the user. It is recommended to use an exhaust system if spray method is used in a confined place.

Penetrant has been sprayed on to this small component.The component is placed on the grid for dwell.

Use of breathing apparatus and an exhaust system is very essential for spray applications in confined places.

For small parts, penetrant may be applied by dipping the part into a tank containing the penetrant. Suitable baskets are available for this application.The material of the basket shall not contaminate the penetrant materials.

A basket with some parts inside, is being lowered on to a fluorescent penetrant tank.

Parts of smaller size or a number of small parts may be placed on a basket and dipped in the penetrant tank.• Large part may be lowered on to the tank by chain hoist.• Dipped part should be removed

from the tank for draining.

If penetrant is applied by dipping, there must be a place for draining excess surface penetrant from the part.

A number of small parts are being sprayed with fluorescent penetrant from a spray can.

Penetrat spray using pocket size aerosol cans for spot testing in the field:

Penetrat static spray using pocket size aerosol cans for spot testing in the field:

Conventional method of penetrant application for solvent removable penetrant process is to spray from an aerosol can.

A penetrant application booth with exhaust system over the application table.

A spray application section with the exhaust system above.

A booth for electrostatic spray application :This method has been reported to cause slightly increase in the sensitivity of examination. Electrostatic spraying is applicable both for penetrant and developer applications.

Drain and Dwell :If immersion method of application is used, It is not recommended to leave the part dipped in the penetrant tank during the dwell time.

After the dip applicationnt, the part is allowed to drain the excess penetrant throughout the dwell time.

Penetrant may be reapplied if there is tendecy of the penetrant to dry.

A part covered with fluorescent penetrant has been placed on the grid for draining during the dwell time.

Parts covered with fluorescent penetrant is placed on the grid to drain during dwell time. If penetrant appears to be drying during the dwell time, penetrant must reapplied.

Parts during dwell time.

The entire test area must be fully covered with a thin layer of penetrant. A Part covered with visible penetrant is under dwell time :

Penetrant applied on welded joints.

Dwell time chart :Dwell time is the time allowed for penetrant to enter discontinuities. Tight discontinuities require longer dwell time.

Suggested timing for some common product forms :

A cubicle for penetrant testing of precision parts.

Simple penetrant application table with the exhaust system on top.

A Penetrant test cabin for spray application of aerospace components.

Automatic penetrant applicatin system :

Fully automatic penetrant test line :

Large scale Penetrant testing line 1 :

Penetrant test line 2 :

Final inspection booth :

Penetrant tank processing layout for a Lab :

Applicable for fluorescent and color contrast examination.

The tank systems in a small laboratory setup.

A compact fluorescent processing set up. Black curtained area is the examination zone. up.

Developer application and Inspection booth with UV lamp for the fluorescent process.. Exhaust line can be seen on the top.

Darkened area for large scale fluorescent Inspection process.

Professional compact set up :• A compact professional setup with Electrical power, Exhaust system, Sprayer system, Ordinary and UV lights, and water treatment system.

A simple container can be set up for use with the solvent removable test process. Provision of electrical supply and darkening the inside area permits fluorescent process also.

Solvent Removable Method : uses Solvents as penetrant remover.* Solvent method is highly sensitive, does not require additional

equipments.* Recommended for spot testing.* Most suitable for field use.* Requires careful processing.* Shall not be used near open flame.

Solvent removable Penetrnt test kit.

Solvent Penetrant set for portable use :The set consists of Cleaner, Penetrant and Developer in Aerosol cans which can be used in most locations.• Cleaner is a volatile solvent for the penetrant in use.• Penetrant for this process is usually oil based and can not be removed by water rinsing.• Developer is usually white powders suspended in a volatile solvent.• The aerosol cans have shelf life of 5 years. However, the loss of pressure may affect the cans after 2 years.

Solvent process : step 1Precleaning

• After the part surface is prepared for the examination, cleaner is sprayed on to the test surface to remove traces of oiliness.• The surface is allowed to dry by evaporation or wiping.

Solvent process : step 2Penetrant application

• The part surface must be completely dry before penetrant application.• The penetrant is brushed / sprayed on the entire test area in a thin film.• The penetrant is then allowed to dwell on the part surface for the required time.• The penetrant must not dry during the dwell time.• Penetrant may be reapplied during the dwell time.

Solvent process : step 3Removal of excess penetrant.

• The part surface is wiped with clean dry cloth, followed by fresh solvent dampened cloth.• Wiping is repeated until no traces of penetrant is visible on the rag.• Penetrant wiping shall be done carefully otherwise it will remove penetrant from the discontinuities affecting the sensitivity of examination.

Solvent process : step 4

• A developer is used to complete the examination process.• Developers are inert white powders used dry or as a liquid suspension. • The developer is sprayed carefully to cover the entire test area in a thin uniform coating.• Avoid wet runny coating.

Solvent process : step 5

• Gross discontinuities produce immediate indications.• Tighter discontinuities take longer time to produce indications. • A minimum of 7 minutes development time is recommended.• The size of the indications gives relative idea of the nature of the discontinuities.

The solvent process summary :

Incorrect application of developer : A wet runny coating. Developer sprayed from a short distance without shaking the can. Excess liquid run away without leaving sufficient developer particles.

Correct application of developer :A thin uniform and continuous coating must be applied. Solid white coating is not required.

Solvent penetrant must be removed by wiping :Excess loose penetrant is wiped off by clean dry cloths. The remaining traces are removed using solvent dampened new cloth. After one pass, the cloth is folded to expose clean surface, dampened with the solvent, and the surface is wiped again. The surface of the cloth is examined, if traces of penetrant is visible, the cloth is folded to expose clean surface, dampened again with the solvent and the surface is wiped again. The process is continued till no traces of penetrant is visible on the cloth surface. The solvent shall not be sprayed directly on the test surface.Cleaning shall be along one direction only.

Lint free clean cloth for wiping solvent type penetrants.

Crack indication at the eye of a Lug, revealed by solvent removable color contrast penetrant process.

Solvent type penetrant applied around the nozzle weld.

Excess penetrant removed and developer applied.

Color contrast indication from a crack. Pink coloration of the developer is due to insufficient removal of excess penetrant. The applied developer must not flow.

Solvent type penetrant is being sprayed on to the part.

Color contrast indication of cracks on the part.

Color contrast indication from a crack on the part. A small rounded indication can also be seen.

Color contrast crack indication on a welded plate :[ Solvent removable process ]

Crack indication on a blade, revealed by color contrast solvent removable penetrant process.

Most simple penetrant test set for spot testing [ penetrant Pens for field use ] :Fluorescent, Dual sensitivity, Remover and non aqueous Developer.

Water washable Method :for fast and economical processing of large number of parts.

* These Penetrants can be washed directly with water. * Water washable penetrants contain an emulsifier which make them water washable.* Emulsifier increases the viscosity which calls for longer penetration time.* These penetrants can not enter very tight discontinuity opening.* Because of easy washability, water washable method is not suitable for wide shallow discontinuities. * These penetrants are used where high sensitivity is not required.* Good for examination on rough surface, threads, keyways, narrow grooves and where liquid has a tendency to accumulate. Water washable method is less sensitive when compared to solvent and post emulsification methods.

Water washable process : fast & economical * After the penetration time, the part is rinsed with plain water to remove the excess surface penetrant.* Rinsing is performed with a coarse water spray from a nozzle, at around 450 to the surface, from a distance of 6 to 12 inches.* Water pressure, nominal 40 PSI, max 50 PSI, temp 10 – 380 C* Maximum rinsing time for any area shall not be more than 2 minutes.

A water spray gun for rinsing operation : Factory adjusted to 40 PSI pressure.For large scale processing, pressure gauges are recommended to control the rinsing process.

A coarse water spray removes loose penetrant by scrubbing action :

A part being rinsed from a water spray gun :

Rinsing Tank.

Rinsing Tank : pressure gauges for controlling nozzle pressure. Uv lamp for washing fluorescent penetrants.

Rinsing Tank.

Post Emulsification Method :

Highly Sensitive penetrant examination.Uses an external emulsifier to make the penetrant water washable.

Two types of Emulsifiers are used

Lipophylic [ oil based ] work by diffusion process.Hydrophylic [ detergent based ] works by scrubbing action.

Lipophylic [ oil based ] Emulsifier :works by diffusion process. Emulsification time is critical and depends on roughness, viscosity of emulsifier, temperature.

• Once the penetration time is over, the part is dipped into the emulsifier tank and removed for draining.• With time, the emulsifier diffuses into the penetrant layer and the resulting mixture is water washable.• Excess penetrant is then removed by water rinsing.• Emulsification time varies between 1 to 4 minutes and must be determined practically for each type of parts. • Emulsifier can not be applied by a brush.

Lipiphylic Emulsifier process :oil based emulsifier, applied by dipping the part in the emulsifier tank. The emulsifier is then allowed to act for a controlled period of time. The resultant mixture is water washable and to be removed by water rinsing. The emulsifier in the tank gradually gets contaminated by penetrant and is finally discarded when contamination exceeds 20%.

Hydrophylic [ detergent based ] Emulsifier :Most used emulsifier process. Loose penetrant is first removed by plain water rinse. The remaining penetrant is then removed by spraying the part surface using 2.5 to 5% solution of emulsifier. The emulsifier may also be used by immersing the part in a 10 to 30% emulsifier solution with mild agitation. The part surface is then sprayed with plain water again to remove residue of the emulsifier solution.These emulsifiers are less sensitive to contact time and is easy to control than the lipophylic emulsifier process.

Hydrophylic Emulsifiersolution Concentration :The concentration plays an important role in excess penetrant removal process. The concentration is monitored using a refractometer.

Developers :

there are 4 Forms of Developers :

Dry developers.[ Chemically inert white powders ]

Aqueous [ water base ] Water solution developers. [ water soluble particles ]Water suspension developers. [ insoluble particles ]

Non AqueousSolvent suspension developers.[ insoluble particles ]

Devloper action [ blotting ] :Developer extracts penetrant from discontinuities by blotting action.Provide contrasting background.Penetrant spreads through the developer and magnifies the indication making it more visible to the eye.

Developer Spray :A thin uniform coat of developer is required to initiate the blotting action. Thick coating masks weaker indications must be avoided.

Dry developer application : Dry developers are normally used with fluorescent process only.Can be applied by dipping, scooping, brushing and spraying. Electrostatic charged spraying or dust chamber application is most suitable. The developer must cling to the surface in a fine film of dust. Dry developer must be applied on a dry surface only.

Dry developer application by scooping :Dry developers are normally used on rough surfaces.Applied by dipping, scooping and brushing. Excess developer is removed by shaking and gentle air blast.

Dry developer application in a dust storm closed cabinet :Dried parts are placed on the grid, the cabinet is closed and the powder is blown by moisture free compressed air or a fan mounted at the bottom of the cabinet to form a cloud of dust. While settling the powders coat the part surfaces.

Water soluble developer : Water soluble developer particles dissolve in water to produce a clear working solution. Water suspension developer is suspension of insoluble particles in water. Suspension developer requires continuous agitation during use. Application by spraying and dipping is recommended. [ dipping is not allowed for water washable type penetrants ] After the application of developer, parts require drying in a temperature controlled oven.

Non aqueous developer is being applied by spraying :The recommended method of application of non aqueous developer is by spraying. A thin uniform coat is applied to the part surface by spraying from a suitable distance. A wet runny coating must be avoided.

Non aqueous developer applied by spraying :A thin uniform coat has been applied. Solid white coating is not required. Solid coating masks weak indications.

A part after developer application :The defect indications are highlighted with a red marker pen.

Solvent suspension developer applied. Removing excess penetrant by manual wipe from a large object is a tedious task. The pink traces are the residue of penetrant left out during excess removal.

A large crane hook undergoing penetrant examination :

Summary of penetrant processes.

Examination for indications : the penetrant spreads and produce an enlarged indications.

Penetrant Indications :The penetrant bleeds in to the developer and produces enlarged indications.

Discontinuity Indications :The dye spreads on the developer and the indication is larger than the discontinuity opening.

Color contrast Indication :Crack at the junction of a weld visible under ordinary lighting. Gross defects produce dark red indication because of good bleed out. Good bleed out shows that the discontinuity has volume.

Color contrast Indication :Crack indication. Bleed out shows a gross defect.

Color contrast indication :Dark red indication shows a deep crack.

Crackindication : The indication is less bright because of penetrant spread.

Color contrast Indications :

Bright red indications from deep cavities on a weld.

A long crack indication.

Penetrant indications : [ Both rounded and linear indications ]

Penetrant indications from a number of mostly shallow cracks

Penetrant testing of rail crossings.

Deep crack Indications obtained on the head of the rail.

Liquid Penetrant Indication :Fluorescent indication of a Long crack.

• When the pinholes are located very close to each other, indications overlap to produce patches.

• Numerous crack Indications overlapped to form patches.

Photograph of a Fluorescent Indication :

Fluorescent Indication : a crack originating from a hole.

Photograph of a Fluorescent Indication :

Color contrast Indication :Cracks at the head of a bolt.

Fluorescent Indication :Crack at the head of a bolt visible under ultraviolet illumination.

Fluorescent Indication :The brilliant glow of the fluorescent dye can make small indications clearly visible.

Inspection :

* Indications are interpreted in terms of type and size.* Indications are classified as Linear or Rounded.* Size of the indications are larger than the discontinuity openings. * The size of the indications are the deciding factor.

Linear and Rounded indication :Linear ; Length greater than 3 times the width.Rounded ; Length less or equal to 3 times the width. Accept – Reject decision depends on the type of indication.

Rounded and Linear type of penetrant indication :

Rounded : Length of the indication less or equal to 3 times the width. Linear : Length of the indication greater than 3 times the width.

Rounded penetrantant indications around the hole.

Numerous linear penetrantant indications on this machined part.

Linear indication, from a crack which is not very deep:

Rounded indication from deep cavities :

Linear [ crack ] indication, light coating of developer shows the indications clearly.

Linear indication / crack on the weld surface, indications from undercuts along the weld edges can be seen.

Linear indications [ multiple cracks ] at ID of a tube.:

Example of Linear indication / Crack : A medium deep crack at the edge of a weldLinear indication : Length greater than 3 times the width.

A gear with no relevant surface indications.

Example of Linear indication / a long weld Crack :

Example of Linear indication / Crack :A light coating of developer is required for detecting light indications.

Example of Linear indication : A long weld Crack. Indications from undercuts can also be seen.

A heat exchanger tube to tube sheet welds under penetrant examination.

Heat exchanger tube to tube sheet welds, no relevant indication in this area..

Indications detected by penetrant examination is generally removed by a portable grinder.

After cutting through the defects, the area should be retested before repair to ensure complete removal of the defects.

The indications removed by grinding.the ground area is retested to ensure that the defects have been removed.

The re test of the ground area shows that the defects have been removed.

No relevant penetrant indications on theses cast parts.

Black and white image of a crack indication in a cast part.

inspection booth

An examinar Looking for penetrant indications using UV illumination. Photo taken using white light.

Cast Gear, no relevant indications.

Example of rounded indications / porosity cluster :rounded indication : Length less than or equal to 3 times the width. 4 or more indications in a line with a separation of less than 1.6 mm between each indication is unacceptable.

Example of Rounded indication / Porosity :Rounded indication : Length less or equal to 3 times the width. Rounded indications are generally produced by pinholes, cavities and crater cracks. Single indication larger than 4.8 mm is unacceptable.

Black and white image of rounded indications.

Indications from impact loaded cracks in test samples : Indications from radiating arms overlap to produce large round indication. A weld surface crater crack produce such indications.

Example of indications :

Indication from lack of fusion in ERW joint

Linear indication : [ very deep cracks ]

Non relevant indications :Non relevant indications can be produced by failure to remove sufficient excess surface penetrant.

Patches of penetrants will appear if sufficient excess surface penetrant is not removed.

Non relevant indications :Rough irregular surface makes removing excess penetrant difficult and produce non relevant indications.

Non relevant indications :Non relevant indications can be produced by failure to remove sufficient excess penetrant.

Non relevant indications :Non relevant indications can be produced by failure to remove sufficient excess surface penetran.Roughness and irregularities make removal of excess penetrant difficult.

Non relevant indications :Non relevant indications can be produced by failure to remove sufficient excess penetrantSsurface roughness and irregularities make removal of excess penetrant difficult.

Over removal of penetrant produces diffused indications.

Excess developer coating masks or produce light indications.

Non relevant indications :Insufficient removal of excess surface penetrant will produce Interfering penetrant background.

A crack emanating from the hole. Heavy background because of residual penetrant.

A crack emanating from the cornere. Reddish background because of residual penetrant.

Non relevant indications :failure to remove sufficient excess penetrant produces reddish-white background.

Indications from undercut, rough surface etc.

Over removal of penetrant produces diffused indication

Gross discontinuities have produced dark red indications.

Relevant from holes[ IP ] and and non relevant indications from rough surfaces.

Grooves are difficult to clean may produce non relevant indications :

Crack indication in teeth and some non relevant indications:

Sources of Non relevant indications :

• Tool marks.• Finger prints.• Penetrant patches at the table or at the fingers of the operator.• Lint or dirt particles on surface.• Scales on surface.• Oily residue on surface when fluorescent is performed.

Penetrant indications from surface blemishes.

Penetrant indications from surface blemishes and the one.

Penetrant residue at the fingers of the operator :

Removal of excess penetrant is difficult on rough and corroded surfaces, show up as non relevant indications.

Improper processing may produce weak indications :

Effect of penetrant quality on indications - 1 :

Incorrect applications of developer: Developer shall not flow on the part. A flowing developer will wash out indications.

Correct applications of developer.

Effect of penetrant sensitivity on indications 6 :

Monitoring performance of penetrant test process :

Cracked Aluminum Comparator Block : 2024 – T3 aluminum plate heated and quenched to produce crack patterns. Crack size is uncontrolled. Used for side by side comparison of penetrants.

Indications from crack pattern in the aluminum crack panels.

Comparing fluorescent penetrants by aluminium test blocks.

Penetrant Test panels :Ni - Cr crack panels. These are matched test panels for monitoring sensitivity and comparing penetrants.The crack depth is controlled.The blocks are supplied with photograph or replica of the indications. This 1st record is compared with subsequent tests.The cracks open with use and must be monitored.

Matched Ni – Cr panels and their replica indications.

Ni Cr matched test panels for monitoring sensitivity.

Cross section of crack in Ni - Cr test panel. The width of the crack is 1 / 20 of the crack depth. Sensitivity of crack detection depends mainly on crack width and not on length.

Indications of the cracks in Ni – Cr crack panels.

KnownDiscontinuityStandard[ KDS ] Panels : contains controlled cracksof 5 different sizes and rough surface for checking wash ability.Two panels are produced together for side by side comparison of used and fresh penetrants.

Indications from the cracks in the KDS Panel :

sensitivity is compared by noting the smallest crackdetected.

Two KDS panels are produced together so that they are virtual twins.

Fluorescent Indications of the cracks in the KDS Panel :

Testing and Maintenance [ TAM / PSM 5 ] Panel : Extensively used in aerospace industries and fore runner of modern panels.Contains 5 cracks of different sizes and rough surface forchecking the washing characteristics of penetrants.

Two versions of the TAM / PSM5 Panels : Highly polished and rough surface for testing the washability of penetrant.

Crack indications in the TAM Panel :

Ultraviolet Bulbs [ mercury vapor lamps ] :Low power [ 100 / 125 Watts ] uses an internal deep purple coating as filter for short wave length ultraviolet radiation. The dark color of the coating filters out visible light.High power bulbs uses external [ Koop ] filter. With filter, the bulb transmits 300 to 400 nm wavelength ultraviolet light with peak wavelength around 365 nm.The florescent material coating absorbs this energy and re- emits yellow green light which is highly visible.

1. Ultraviolet lamp external filters :2. Yellow UV filter glasses for reducing eye-strain.

Bulbs with damaged filter or coating must not be used.

Unfiltered ultraviolet light burns the exposed skin and the retina of the eye causing blindness.

Portable UV Light :lamp head with igniter / ballast power supply. The system operates from 110 / 220 v power supply. The bulb becomes very hot.

The head which houses the UV bulb. The head may use external filter if required by the bulb. A plastic pistol grip is used to hold the head during use. An external ballast type power supply provides power to the head. The lamp must be left on unless a long idle period follows. Once switched off, the lamp does not switch on until it cools down sufficiently.

Hand held UV lamp illuminates parts at any location.

Florescent pigments are used for preparing fluorescent penetrants. Under ordinary light, fluorescent penetrants look pale yellow.Fluorescent materials glow brilliantly under ultraviolet illumination. Fluorescent materials used in non destructive testing responds to ultraviolet radiation around 365 nano meters.

The fluorescent dye used in the penetrant absorbs invisible ultraviolet radiation and emits visible light in yellow – green color.

The eye has maximum sensitivity 525 – 575 nm..

Ultraviolet Light illuminating fluorescent materials:

A ring illuminated by ultraviolet light.

Fluorescent indications under ultraviolet illumination :

Appearance of white developer under ultraviolet illumination.The white developer produces a darker background and enhance the indications :

Fluorescent Indications :Surface indications on a chain ring.

• An Inspection booth for fluorescent penetrant examination.• Fluorescent examination process requires darkened inspection area. • Requires light intensity of min 1000μW / Cm2 at the examination surface.• Back ground light must be limited to 20 Lux maximum. • Examination may be performed at normal light using very high power lamps of min 3000μW / Cm2 intensity.

Fluorescent penetrant test process requires a darkened area which can be achieved by use of black curtains. UV lamp is used ;1. Execcss penetrant removal station for checking adequacy of the cleaning operation.2. inspection station for viewing indications.

Battery operated ultraviolet lightFor use in areas where electrical supply is not available. The unit has limited intensity.

UV Light emitting diodes are also used for battery lighting in remote areas.

High intensity ultraviolet flood lamp, produces 7500 – 10,000 μW / Cm2 and allows fluorescent examination without darkening the test area.

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Ultraviolet Light for Flourescent Process :

Material Failure :

A part covered with fluorescent penetrant is placed on the grid to drain during dwell time.

Visible light spectrum

Ultraviolet Bulbs [ mercury vapor lamps ] :Low power [ 100 W ] uses internal coating as filter.High power uses external filter.

• With filter, the bulb transmits 300 to 400 nm wavelength ultraviolet light with peak wavelength of 365nm.

• Bulbs with damaged filter or coating must not be used.

• Without filter if directly exposed it damages human eye and the skin.

• Fluoroscent penetratn testing needs UV light

Non-relevant Indications :

Water washable Penetrants ;Water washable process : fast & economical is used where high sensitivity is not required.Good for examination of rough surface, threads, keyways and large number of parts

Fluorescent Examination Process :Discontinuities detected by a penetrating colored liquid. This color is visible under ultraviolet illuminations. This process is more sensitive than color contrast process. Small indications are easily seen.Fluorescent penetrants are available in five sensitivity levels.½, 1 – 4. Selection rule is to choose the lower sensitivity penetrant which will provide the required sensitivity.

Liquid Penetrant Testing :Discontinuities detected by a penetrating colored liquid.

• Penetrant entered into discontinuties and shows indication

• Linear indication is a indication length greater than three times of the width

• Rounded indication is a indication length atleast equal to three times of width

Solvent Removable Method :


* Solvent method is highly sensitive, does not require additional

equipments.* Recommended for spot testing.* Most suitable for field use.

Fluorescent Indications :Pinholes indication in casting.

• When the pinholes are close to each other, indications overlap to produce patches of indications.

Penetrant application by brush :

Liquid Penetrant Testing :

• Applicable to ferro magnetic

materials, Iron, Cobalt, nickel and their magnetic alloys.

• For detection of surface and sub surface flaws

Welding Cracks :Service induced defects

Liquid Penetrant Testing :defect removal by grinding

Water washable process : fast & economical is used where high sensitivity is not required.Good for examination of rough surface, threads, keyways and large number of parts

Water wash process :


• Applicable to ferro magnetic

materials, Iron, Cobalt, nickel and their magnetic alloys.

• For detection of surface and sub surface flaws

Linear [ crack ] indication :

Non relevant indications :Interfering penetrant background will be produced by failure to remove sufficient excess penetrant.

Liquid Penetrant Testing 2

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