Dye Penetration Test

8/11/2019 Dye Penetration Test

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*mportant considerations

espite being one of the popular *! methods, liquid penetrant testing is often misused

!est surfaces are not cleaned adequately, the contact time between the penetrant and thetest surface is too short, or the excess penetrant is removed carelessly (ie from flaws as

well as from the test surface) "or these reasons, it is important that personnel carryingout liquid penetrant inspection are properly trained and qualified (for example, inaccordance with the +ritish nstitute of *on estructive !esting's .* certification

scheme or equivalent schemes such as those operated by ./0 and #/*!)

Where is it used?

f applied correctly, liquid penetrant testing offers a fast, cheap and relatively simplemeans of surface inspection, making it attractive to a number of industries #t the 'high-

tech' end of the market, the aerospace industry use automated fluorescent penetrant

testing to look for fatigue cracking in turbine blades #t the other end of the scale, theconstruction industry uses dye penetrant testing as a quick and simple method for

checking that welds and other susceptible areas are free from surface-breaking flaws


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$&e penetrant inspection($P*), also called liquid penetrant inspection(LP*) or

penetrant testing(P+), is a widely applied and low-cost inspection method used to

locate surface-breaking defects in allnon-porous materials (metals, plastics, or ceramics)!he penetrant may be applied to all non-ferrous materials, but for inspection of ferrous

components magnetic-particle inspectionis preferred for its subsurface detection

capability L is used to detect casting and forging defects, cracks, and leaks in newproducts, and fatigue cracks on in-service components

1 /ection of material with a surface-breaking crack that is not visible to the naked eye$ enetrant is applied to the surface

2 3xcess penetrant is removed

4 eveloper is applied, rendering the crack visible

Principles

is based upon capillary action, where low surface tension fluid penetrates into clean

and dry surface-breaking discontinuities enetrant may be applied to the test componentby dipping, spraying, or brushing #fter adequate penetration time has been allowed, the

excess penetrant is removed, a developer is applied !he developer helps to draw

penetrant out of the flaw where a visible indication becomes visible to the inspectornspection is performed under ultraviolet or white light, depending upon the type of dye

used - fluorescent or nonfluorescent (visible)

,aterials

enetrants are classified into sensitivity levels isible penetrants are typically red incolor, and represent the lowest sensitivity "luorescent penetrants contain two or more

dyes that fluoresce when excited byultraviolet(-#) radiation (also known as black

light) /ince "luorescent penetrant inspectionis performed in a darkened environment,and the excited dyes emit brilliant yellow-green light that contrasts strongly against the

dark background, this material is more sensitive to small defects
http://en.wikipedia.org/wiki/Porosityhttp://en.wikipedia.org/wiki/Magnetic-particle_inspectionhttp://en.wikipedia.org/wiki/Capillary_actionhttp://en.wikipedia.org/wiki/Fluorescenthttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/Fluorescent_penetrant_inspectionhttp://en.wikipedia.org/wiki/Porosityhttp://en.wikipedia.org/wiki/Magnetic-particle_inspectionhttp://en.wikipedia.org/wiki/Capillary_actionhttp://en.wikipedia.org/wiki/Fluorescenthttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/Fluorescent_penetrant_inspection


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0hen selecting a sensitivity level one must consider many factors, including the

environment under which the test will be performed, the surface finish of the specimen,

and the si5e of defects sought 6ne must also assure that the test chemicals arecompatible with the sample so that the examination will not cause permanent staining, or

degradation !his technique can be quite portable, because in its simplest form the

inspection requires only 2 aerosol spray cans, some paper towels, and adequate visiblelight /tationary systems with dedicated application, wash, and development stations, are

more costly and complicated, but result in better sensitivity and higher sample through-

put

*nspection steps

+elow are the main steps of Liquid enetrant nspection7

-. Precleaning:

!he test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale thatcould either keep penetrant out of a defect, or cause irrelevant or false indications.leaning methods may include solvents,alkaline cleaning steps, vapor degreasing,or

media blasting !he end goal of this step is a clean surface where any defects present are

open to the surface, dry, and free of contamination *ote that if media blasting is used, it

may 8work over8 small discontinuities in the part, and an etching bath is recommended asa post-bath treatment

/. Application of Penetrant:

!he penetrant is then applied to the surface of the item being tested !he penetrant is

allowed time to soak into any flaws (generally 9 to 2% minutes) !he dwell time mainlydepends upon the penetrant being used, material being testing and the si5e of flaws

sought #s expected, smaller flaws require a longer penetration time ue to their

incompatible nature one must be careful not to apply solvent-based penetrant to a surfacewhich is to be inspected with a water-washable penetrant

0. '1cess Penetrant 2emo#al:

!he excess penetrant is then removed from the surface !he removal method is controlled

by the type of penetrant used 0ater-washable, solvent-removable, lipophilicpost-

emulsifiable, or hydrophilicpost-emulsifiable are the common choices 3mulsifiers

represent the highest sensitivity level, and chemically interact with the oily penetrant tomake it removable with a water spray 0hen using solvent remover and lint-free cloth it

is important to not spray the solvent on the test surface directly, because this can theremove the penetrant from the flaws f excess penetrant is not properly removed, once

the developer is applied, it may leave a background in the developed area that can mask

indications or defects n addition, this may also produce false indications severelyhindering your ability to do a proper inspection
http://en.wikipedia.org/wiki/Solventhttp://en.wikipedia.org/wiki/Vapor_degreasinghttp://en.wikipedia.org/wiki/Lipophilicityhttp://en.wikipedia.org/wiki/Hydrophilicityhttp://en.wikipedia.org/wiki/Emulsifierhttp://en.wikipedia.org/wiki/Solventhttp://en.wikipedia.org/wiki/Vapor_degreasinghttp://en.wikipedia.org/wiki/Lipophilicityhttp://en.wikipedia.org/wiki/Hydrophilicityhttp://en.wikipedia.org/wiki/Emulsifier


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3. Application of $e#eloper:

#fter excess penetrant has been removed a white developer is applied to the sample

/everal developer types are available, including7 non-aqueous wet developer,dry powder,water suspendable, and water soluble .hoice of developer is governed by penetrant

compatibility (one can't use water-soluble or suspendable developer with water-washablepenetrant), and by inspection conditions 0hen using non-aqueous wet developer

(*#0) or dry powder, the sample must be dried prior to application, while soluble andsuspendable developers are applied with the part still wet from the previous step *#0

is commercially available in aerosol spray cans, and may employacetone,isopropyl

alcohol,or a propellant that is a combination of the two eveloper should form a semi-transparent, even coating on the surface!he developer draws penetrant from defects out

onto the surface to form a visible indication, commonly known as bleed-out #ny areas

that bleed-out can indicate the location, orientation and possible types of defects on thesurface nterpreting the results and characteri5ing defects from the indications found may

require some training and:or experience

4. *nspection:

!he inspector will use visible light with adequate intensity (1%%foot-candlesor 11%%lux

is typical) for visible dye penetrant ltraviolet (-#) radiation of adequate intensity(1,%%% micro-watts per centimeter squared is common), along with low ambient light

levels (less than $ foot-candles) for fluorescent penetrant examinations nspection of the

test surface should take place after a 1% minute development time !his time delay allowsthe blotting action to occur !he inspector may observe the sample for indication

formation when using visible dye t is also good practice to observe indications as they

form because the characteristics of the bleed out are a significant part of interpretation

characteri5ation of flaws

5. Post "leaning:

!he test surface is often cleaned after inspection and recording of defects, especially if

post-inspection coating processes are scheduled

Ad#antages and disad#antages

!he main advantages of are the speed of the test and the low cost !he main

disadvantages are that it only detects surface flaws and it does not work on very rough

surfaces #lso, on certain surfaces a great enough color contrast cannot be achieved or thedye will stain the workpiece

Limited training is required for the operator ; although experience is quite valuable

roper cleaning is necessary to assure that surface contaminants have been removed and

any defects present are clean and dry /ome cleaning methods have been shown to bedetrimental to test sensitivity, so acid etching to remove metal smearing and re-open the

defect may be necessary
http://en.wikipedia.org/w/index.php?title=Non-aqueous_wet_developer&action=edit&redlink=1http://en.wikipedia.org/wiki/Acetonehttp://en.wikipedia.org/wiki/Isopropyl_alcoholhttp://en.wikipedia.org/wiki/Isopropyl_alcoholhttp://en.wikipedia.org/wiki/Foot-candleshttp://en.wikipedia.org/wiki/Luxhttp://en.wikipedia.org/w/index.php?title=Non-aqueous_wet_developer&action=edit&redlink=1http://en.wikipedia.org/wiki/Acetonehttp://en.wikipedia.org/wiki/Isopropyl_alcoholhttp://en.wikipedia.org/wiki/Isopropyl_alcoholhttp://en.wikipedia.org/wiki/Foot-candleshttp://en.wikipedia.org/wiki/Lux


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Liquid $&e Penetrant +est- # liquid penetrant test is non-destructive type t detects

flaws that are open to the surface eg, cracks, seams, laps, lack of bond, porosity, cold

shuts, etc t can be effectively used not only in the inspection of ferrous metals but isespecially useful for non-ferrous metal products and on non-porous, non-metallic

materials such as ceramics, plastics and glass

!he principle of liquid penetrant test is that the liquids used enter small openings such ascracks or porosities by capillary action !he rate and extent of this action are dependent

upon such properties as surface tension, cohesion, adhesion and viscosity

!hey are also influenced by factors such as the condition of the surface of material and

the interior of the discontinuity "or the liquid to penetrate effectively, the surface of thematerial must be thoroughly cleaned of all foreign matter that would obstruct the entrance

of the liquid into the defect

#fter cleaning, the liquid penetrant is applied evenly over the surface and allowed toremain long enough to permit penetration into possible discontinuities !he liquid is then

completely removed from the surface of the component and either a wet or a dry

developer is applied !he liquid that has penetrated the defects will then bleed out ontothe surface, and the developer will help delineate them!his will show the location and general nature and magnitude of any defect present !o

hasten this action, the part may be struck sharply to produce vibrations to force the liquid

out of the defect !he oil-whiting test is one of the older and cruder penetrant tests usedfor the detection of cracks too small to be noticed in a visual inspection n this method,

the piece is covered with penetrating oil, such as kerosene, then rubbed dry and coated

with dry whiting

n a short time the oil that has seeped into any cracks will be partially absorbed by thewhiting, producing plainly visible discolored streaks delineating the cracks

!he ye penetrant test (!) based on liquid penetrant is a sensitive extremely versaliteand a very reliable method of test t is quite inexpensive, does not require any specialapparatus and is quite simple in application 6nly a moderate skill is required n this test,

the strongly coloured red penetrant fluid (or dye) has a property of seeping into surface

flaws when applied on an impervious surface!he steps involved in dye penetrant test are

(1) .lean the surface of the component free of dust and dirt with a piece of cloth

($) +rush the surface of the component to remove scale, rust, paint etc, by a soft wire

brush(2) /pray the cleaner to remove oil, grease, etc

(4) #pply the dye penetrant (by spraying) adequately to cover the area to be tested #llow

2 to 9 minutes or more for dye to penetrate into the cracks(9) 0ipe off the excess penetrant on the surface with a rag

() !he crack if any will be indicated with the red dye absorbed by the white absorbent

Documents

Dye Penetration Test