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IntroductionLiquid penetrant testing is a nondestructivemeans of locating surface discontinuities based

on capillarity or capillary action.

The liquid penetrant method , the liquid isapplied to the surface of the specimen, and

sufficient time is allowed for penetration of

surface discontinuities. If the discontinuity is

small or narrow , as in a crack or pinhole ,capillarity assists the penetration.

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DEVELOPMENT

Historically , penetrant inspection was called

the oil and whiting method as it used

kerosene and a white powder for the inspection

of railed road parts. However , in the past 40

years the process has been improved

tremendously top the point where it is a

reliable and accurate inspection technique.

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After sufficient time haspassed for the penetrant to

enter the discontinuity, the

surface of the part is cleaned ,capillary action is again

employed to act as a blotter todraw penetrant from the

discontinuity.

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To insure visibility , the liquidpenetrant contains either a colored

dye easily seen in white light, or a

florescent dye visible under blacklight.

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LIMITATIONS

Discontinuities that are subsurface in stage of

production could be open to the surface at another

stage, such as after grinding , machining.

Nonmetallic inclusions and porosity in the ingotmay cause stringers, seams forging laps. Cold

shuts, and the like as the billet or slab is processed

in the manner shown below.

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BEWARE OF THINGS

Anything that could block the penetrant from enteringthe discontinuity must be removed.

A last of contaminates that must be removed wouldinclude dirt, grease, rust, scale, acids, and evenwater. The cleaning solvent used must be volatile (Readily vaporized) so that it easily evaporates out ofthe discontinuity and does not dilute the penetrant.

Surface preparation by shot or sandblasting is notrecommended.

Discontinuities that were open to the surface may beclosed by the shot or sand blasting

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TYPES OF PENETRANTS

VISIBLE DYE PENETRANTS

FLORESCENT PENETRANTS

DUAL SENSITYVITY PENETRANTS

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CATEGORIZED BY THE PROCESSES USED TO REMOVE THE

EXCESS PENETRANT

WATER WASHABLE

POST EMILISIFIED

SOLVENT REMOVABLE

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WHY CLEANING IS REQUIRED?

IF THE SPECIMEN IS NOT CLEAN ANDDRY, PENETRANT TESTING ISINEFFECTIVE

IF ALL TRACES OF PENETRANTMATERIALS ARE NOT REMOVED AFTERTHE TEST, THEY MAY HAVE AHARMFUL EFFECT ON THESPECIMEN.(CHLORINE AND SULFARMAY AFFET SOME ALLOYS)

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DIFFERENT CLEANING

METHOD

DETERGENT CLEANING

VAPOUR DEGREASING

STEAM CLEANING

SOLVENT CLEANING

ALKALINE CLEANING

ETCHING(ALKALINE SOLUTION)

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WHY SURFACE CLEANING NOT

RECOMENDED?

SURFACE CLEANING PROCESSES TEND

TO CLOSE DISCONTINUITIES BY

PEENING OR COLD WORKING THE

SURFACE OF THE SPECIMEN

THESE PROCESSES ARE SHOT

BLASTING, SAND BLASTING, GRIT

BLASTING, LIQUID HONING, EMERYCLOTH AND METAL SCRAPPERS.

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SELECTION OF BEST PROCESS

Sensitivity required

Number of articles to be tested

Surface condition of part being inspected

Configuration of test specimen

Availability of water, electricity , compressed

air, suitable testing area, etc.

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ADVANTAGES OF PENETRANT

TESTING

Penetrant testing is successfully used on metals suchas aluminum, magnesium , brass, copper, cast iron,stainless steel , titanium, and most other commonalloys.

It ca also be used test other materials , includingceramics plastics , molded rubber, powdered metalproducts, or glass.

Penetrant testing is limited by its inability to , testmaterial with discontinuities that are not open to thesurface or having an extremely porous surface.

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PENETRANT TEST EQUIPMENT

(STAINNARY)

Pre-cleaning station (usually in remote area)

Penetrant station (Tank)

Drain station

Emulsification station (Tank) Rinse station (Tank)

Developing station( Tank)

Drying station (Usually oven)

Inspection station (Enclosed booth or table withproper lighting)

Post cleaning station (Usually in remote area

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VISIBLE PENETRANT TEST

EQUIPMENT (PORTABLE)

A visible dye penetrant kit usually contains:

Pressurized spray cans of cleaning or removal

fluid.

Pressurized spray cans of visible dye

penetrant

Pressurized spray cans of non-aqua'sdeveloper

Wiping cloths and brushes

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FLOURESCENT DYE

PENETRANT EQUIPMENT

A Fluorescent dye penetrant kit usually contains:

A portable black light and transformer

Pressurized spray cans of cleaning or removal fluid

Pressurized spray cans of fluorescent dye penetrant

Pressurized spray cans of non-aqueous developer

Wiping cloths and brushes

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PENETRANT TESTING

MATERIALS

SOLVENT REMOVABLE PENETRANTS

WATER WASHABLE PENETRANTS

POST EMULSIFIABLE PENETRANTS

EMULSIFIERS

REMOVERS(SOLVENT)

DRY DEVELOPERS

WET DEVELOPERS

NON AQUEOUS WET DEVELOPERS

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CHARECTERISTIC PENETRANT

Readily penetrate very fine openings Be able to remain in relatively coarse openings.

Not evaporate or dry too rapidly.

Be removed easily from the surface on which it has been applied.

Bleed from discontinuities when developer is applied.

Have ability to spread out in very thin florescence, even when spread

in very thin films. Have permamnce of colour in exposure to heat , light and / or black

light.

Have great brilliance of colur or fluorescence, even when spread invery thin films.

Be inert with respect to the materials being tested and to thecontainers

Odorless.

Nonflammable.

Stable under conditions of storage and use

Nontoxic

Low in cost.

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CHARACTERISTICS OF

DEVELOPER HIGH ABSORPTION TO OCCURE MAXIMUM BLOTTING ACTION

ESAILY DISPERSED TO EXPOSE THE DISCONTINUITYBY ASMALL AMOUNT OF PENETRANT COVERING A LARGESURFACE AREA. THIS PROVIDES A STRONG INDICATION WITHSHARP DEFINITION.

PROVIDE A CONTRAST BACKGROUND FOR INDICATIONS,PARTICULARLY WITH VISIBLE DYE PENETRANTS.

EASILY EVENLY, AND READILY APPLIED.

FORM A THIN UNIFORM COATING OVER THE SURFACE.

EASILY WET T ALLOW PENETRANT TO SPREAD OVER THEPARITICLE SURFACES.

NONFLUORESCENT IF USED WITH FLOURESCENT PENETRANT EASILY REMOED AFTER THE INSPECTION IS EQUIPMENT BEING

USED.

NONTOXIC

INEXPENSIVE

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TYPES OF DISCONTINUITIES

INHERENT

INHERENT WROUGHT

DISCONTINUITIES

INHERENT CAST DISCONTINUITIES

PROCESSING DISCONTINUITIES

SERVICE DISCONTINUITIES

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QUIZ

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