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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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