water in oil what's the big deal
TRANSCRIPT
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Water In Oi lWhat's The Big Deal?
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Water In Oil , What's the Big Deal?
Waterrepresentsarealrisktoequipmentand
shouldbe
aggressively
controlled.
Moisture
in
hydraulicfluidsandlubricatingoilshasa
degradingeffectonboththelubricantandthe
machine.Althoughsomeadditivesclingtothe
waterandareremovedwhenthewater
separatesfromtheoil(knownaswater
washing),othersaredestroyedbywater
inducedchemicalreactions(oxidationand
hydrolysis).Wateralsopromotesoxidationof
theoilsbasestock,increasingtheriskofsludge
andvarnish
formation.
Water
also
causes
rust
andcorrosionofmachinesurfacesandreduces
critical,loadbearingfilmstrength.
Watercoexistswithoilinadissolved,
emulsified,orfreestate.Freeandemulsified
waterposethegreatestrisktothemachineand
thelubricant,andtheyshouldbecarefully
monitoredandcontrolled.
Three Forms of Water
1. Dissolvedwater referstowaterthathasbeenchemicallyabsorbedintotheoil.Whiledissolved
waterpossessesnodirectthreattothecomponentbeinglubricated,itspresencecanserveasa
catalystto
oxidation.
Dissolved
water
is
normally
not
visible
in
an
oil.
2. Emulsifiedwateriswaterthatmaintainsitschemicalintegrity,butisheldinsuspensioninthe
oilbyadditivesandcontaminants.Emulsifiedwaterwillseverelyaltertheloadhandlingability
ofanoil.Whentemperatureandpressureareappliedtoacontaminatedfluid,theoxidation
processissignificantlyaccelerated,leadingtoprematuredegradation.Internalcorrosionand
rustwillalsoresultinallareasofthesystem.Whenanoilhasemulsifiedwater,itwilltakeona
hazyormilkyappearance.
3. Freewater describeswaterthatispresentintheoil,butnotheldinsuspension.Sinceoiland
waterdontmix,anoilsbasestockwillbeconstantlytryingtoseparatefromwater.Without
additivesorcontaminantstobondwiththewater,itwillseparaterapidlyandsettletothe
bottomoftheoil.Freewaterwillbevisibleinanoilasaseparatephaseatthebottomoftheoil
reservoir.
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Effects on Lubrication
Ingeneral,waterisapoorlubricant.Proper
lubricationisdependentontheformationofan
oilfilmtoseparateopposingfrictionsurfaces.
Whenpressureisappliedtoanoilfilm,theoils
viscositywillincreaseproportionallytomaintain
protection.Waterdoesnotexhibitthis
tendencyandwillcauseboundarylubricationto
occurwherefullfluidfilmlubricationwould
otherwisebepresent.
AlarmLimits
Waterisconsideredtobeamongthemost
detrimentalofpossiblecontaminants.Studies
haveshownthatwaterpresentatanylevelcan
reducebearinglifefrom10to100times.While
theoveralltoleranceforwatervariesfrom
machinetomachine,agoodgeneralalarmlimit
forwatercontaminationis0.05%(500ppm).
Somesystemsmaybemoretoleranttowater,
whileothersmaybemoresensitive.Some
manufacturershavesetlimitsaslowas30ppm.
Best practicewouldtendtoindicatethatitis
beneficialtokeepwatercontaminationatthe
lowestlevelpossible.
Controlling WaterContamination
Controllingwatercontaminationrequirestwo
individualconsiderations.First,wemust
addresstheissueofkeepingwateroutofthe
system.Watercancontaminateasystemby
condensationwhenmoistairentersthe
componentandachangeintemperaturecauses
thewatertocondenseanddropintotheoil.
Watercanalsoenterasystemthroughnon
dryingbreathers,faultyhatchesandseals,and
internallyfromleakingheatexchangers.
Second,stepsmustbetakentoremovewater
onceithasenteredasystem.Thiscanbe
accomplishedwithphysicalfiltration,vacuum
dehydration
or
centrifuge.
For
systems
prone
tocontamination,thesetypesofpurification
canbeinstalledinthesystemtoremovewater
continuouslyorondemand.
Systemsthatarepronetowatercontamination
shoulduseanoilthatrapidlyseparatesfrom
water.Anoilsabilitytoseparatefromwateris
knownas
its
demulsibility.
High
detergent
oils
tendtobepoordemulsifiers,whileturbineoils
andmanyindustriallubricantshavebetter
demulsibility.Circulatingsystemsproneto
waterinflux,suchasthosefoundinrollingmills
andpowergenerationplants,cansimplydrain
thewaterfromthereservoirtocontrol
contamination,providedtheoilexhibitsgood
demulsibility.Inthesesituations,theoils
demulsibilityshouldbemonitoredtoensure
thatwatercontaminationdoesnotreachthe
lubricatedcomponents.
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Screening for Moisture: Crackle Test
Oneoftheeasiestwaystomeasurethe
presenceof
free
and
emulsified
water
in
oil
is
withthehotplatecrackletest.Anemulsionis
thestablestateofphysicalcoexistenceof
chemicallyinsolublesubstances,likeoiland
water. Additivesandimpuritiesthatlowerthe
oil'ssurfacetensioncanserveasagentsto
strengthentheemulsion. Waterisinafree
statewhenundissolvedglobulesofwaterare
physicallysuspendedintheoil.
Foryears,oilanalysislaboratorieshave
screenedsampleswiththecrackletest,
performingmoredetailedanalysis,suchasthe
KarlFischertest,onlywhenthecrackletestis
positive.
Inthecrackletest,adropofoilisplacedona
hotplatethathasbeenheatedtoapproximately
400F. Thesamplethenbubbles,spits,crackles,
orpopswhenmoistureispresent.Ifthecrackle
testisnegative,itsimplymeansthatthelevelof
waterpresentinthesampleisbelowthe
detectionlimit;itdoesntnecessarilymeanthe
sampleis
void
of
water.
Sometimesthecrackletestmaynotbe
appropriateandyouwouldneedaKarlFischer
testdoneonallsamplesfromthatmachine.
Thecrackleisnotascientifictestbutan
estimatethat
is
affected
by
oil
type.
KarlFischerorCrackle?
Herearesomequestionstothinkaboutto
helpyoudecidewhichtesttorequest:
Whatisthedetectionlimitforthe
test?
Doesthedetectionlimitchange
dependingonthelubricanttype?
Doyouknowwhatyourlimitsfor
watershouldbe?
Howimportantisittoknowany
watercontamination?
Aredetectionlimitsabovemy
condemnationlimits?
Thefollowingsectionsexplainthesideeffects
ofwaterinoilanddescribeastudyperformed
byTestOilanalyststomeasurethe
effectiveness
of
the
crackle
test.
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Check Out The Limitations of The Crackle Test
Inanefforttocommunicatethelimitationsof
thecrackle
test
in
detecting
water
contamination,TestOilembarkedonalabstudy
touncovercrackledetectionlimits.Atotalof
493samplescomprisedofavarietyoflubricant
typeswererunona400Fhotplate.The
sampleswereassessedforapositiveor
negativecrackle.Thesesamesampleswere
thenanalyzedforwatercontaminationusinga
KarlFischer
titration
(ASTM
D6304
C).
The
waterresultswererecordedinpartspermillion
(ppm).Thetablebelowsummarizestheresults
ofthestudy.Thetablelistsoiltype,thenumber
ofsamplesinthestudy,thedetectionlimit
range,thelowestnegativecracklevalue,and
thehighestpositivecracklevalue.
Thelowestpositivevaluesrepresentthose
samplesthat
exhibited
apositive
crackle
and
theassociatedKarlFischerresultwhilethe
highestnegativevaluesrepresentthose
samplesthatclearlyhadwaterpresent
accordingtotheKarlFischerresults,yetdidnt
crackle. Clearly,thestudydemonstratesthat
quiteabitofvarianceexistsinthewater
detectionlimitofthecrackletest.Youreally
needto
know
your
lubricant
type
before
makingassumptionsonwhatthecracklecan
detect.Insomecases,yourwaterlimitsmayfall
belowcrackledetectionandrunningtheKarl
Fischertestoneverysamplemaybeworththe
cost.
OILTYPE SamplesTested DetectionLimit(ppm)Lowest
Positive(ppm)
Highest
Negative(ppm)
Turbine 111 110610 110 610
MineralGear 62 2401190 240 1190
SyntheticGear 86 100460 100 460
AWHydraulic 86 320750 320 750
PolyolEster 36 3401830 340 1830
PhosphateEster 37 4501140 450 1140
Engine
40
320580
320
580
WindTurbine
(Optigear) 35 7801070 780 1070
Combined 493 1001830 100 1830
Make sure you understand the detection l imits for thecrackle test and know your lubricants tolerance for water.
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Quanti fying the Amount of Water: Karl Fischer Water Test
Ifacrackletest(seetheprecedingsection)is
positive,furthertestingisneededintheformof
theKarlFischerWaterTest.TheKarlFischer
coulometricmoisturetestisaseriesofchemical
reactionsdiscoveredin1935bytheGerman
chemistKarlFischer.Thismethodanalyzes
waterinthemicrogramorpartpermillion
range.Thistestisveryaccurate,to.001%.
WaterdeterminationbyKarlFischerisdefined
inASTM
D
6304.
Forthistest,asampleofoilisintroducedintoa
titrationvesselinknownmassorvolume.Any
waterpresentinthesamplewillreactwith
iodineinthetitrationvessel.Theamountof
iodinerequiredtoreactwiththewaterandthe
knownmassorvolumeofthesampleareused
tocalculate
the
amount
of
water
present
in
the
sample.Resultscanbeclearlyexpressedin
percentorpartspermillion.
Anelectriccurrentpassesthroughagenerator
containingaKarlFischersolution.Iodineis
producedattheanodethatconsumesthe
waterintheintroducedsample.Whenan
excessofiodineisdetected,theanalysisis
complete.Inchoosingthismethod,makesure
thattestspecimensarecompatiblewiththe
chosenreagentandthatnosidereactions
occur.Thismethodistypicallyusedtoanalyze
hydrocarbons,alcohols,andethers.Note:
AnalysisofketonesmustemployaKarlFischer
solutionthatisspecificallyformulatedfor
ketoneanalysis.
Lowlevelsofwater(lessthan2percent)are
typicallytheresultofcondensation.Higher
levelscanindicateasourceofwateringress.
Watercanenterasystemthroughseals,
breathers,hatches,
and
fill
caps.
Internal
leaks
fromheatexchangersandwaterjacketsare
otherpotentialsources.
Remember This...
Whenfreewaterispresentinoil,itposesa
seriousthreattotheequipment.Waterisavery
poorlubricantandpromotesrustandcorrosion
tothecomponents.Dissolvedwaterinanoil
promotesoiloxidationandreducestheload
handlingabilityoftheoil.Watercontamination
canalsocausetheoilsadditivepackageto
precipitate.Waterinanyformcauses
acceleratedwear,increasedfriction,andhigh
operatingtemperatures.Ifleftunchecked,
water
can
lead
to
premature
component
failure.
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Analystsinmakingequipmentandlubrication
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