Monitoring and Alarming Wear Metals
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Transcript of Monitoring and Alarming Wear Metals
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7/26/2019 Monitoring and Alarming Wear Metals
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Alarming
Monitoring
Wear Metals
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Table Of Contents
WhatAlarmLevelsMeanforMachineWear ............................................................................................................................................. 3
UnderstandingAlarmLevels....................................................................................................................................................................... 4
BlendingTheTechniques ............................................................................................................................................................................ 7
AboutTESTOIL............................................................................................................................................................................................. 8
ContactUs................................................................................................................................................................................................... 8
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What Alarm Levels Mean for Machine Wear
Whileitiscertainlytruethat
maintainingahealthy,cleanlubricant
willminimizemachinewear,thereare
stillmanywearmodesthatcanarisein
spite
of
these
efforts
misalignment,
imbalance,overloading,improper
installation,fatigue,andthelistgoes
on.Abnormalwear,forwhatever
reason,happensmoreoftenthanwe
liketothinkabout.Therefore,itis
essentialtohaveastrategyinplaceto
monitormachine
wear.
Oilanalysisremainsthebesttoolfor
earlydetectionofwearproblems.
Wearmetallevelsdetectedusing
spectroscopywillbegintorisewell
before
the
machine
exhibits
symptoms
intheformofvibration,temperature,
ornoise. Asweseeincreasinglevels
weneedtodetermineanappropriate
alarmleveltoalertusofapotential
problem. However,itisverydifficult
todeterminewhatalarmstosetfor
wearmetal
levels
particularly
in
industrialapplicationswhere
equipmentcategories,suchas
gearboxes,aresogeneral.
Doyouknowhowmuchironistoo
muchinagearbox?Considerhow
manydifferent
sizes,
types,
loads,
environments,andapplicationscould
beincludedinthatquestion. Nowadd
themanylubricationsystemsand
lubricanttypesthatareinuse.This
simplequestionbecomesmuchmore
complicated. Doesitseemrealistic
thattherecouldbeagoodanswerto
suchaquestion?Probablynot.Yetin
mostcases,thisisexactlythetypeof
questionthatweareaskingeachtime
we
take
an
oil
sample.
If
we
expect
our
oilanalysisprogramstodetect
machinewearproblemseffectively,we
needtoaskbetterquestions.
Whatwereallywanttoknowiswhatis
normal.Butfirstweneedtodefine
normal.According
to
Websters
Dictionary,normalisconformingtoa
usualortypicalpattern.Nowweare
gettingsomewhere.
Nowhowcanweidentifyapatternina
broadcategorysuchasgearbox? The
answeris
really
fairly
simple
by
evaluatingasmuchdataaswepossibly
can.However,beforewegettoofar
intothis,letslookathowwearmetals
havetraditionallybeenevaluatedin
thepast.
Inoilanalysiswellplacedalarmsandlimits
areliketripwiresalertingoperatorsand
technicianstoathreateningcondition.
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Understanding Alarm Levels
Fixed Limits
Manyprogramshaveusedfixedlimits,
whichgivesasimplepassorfailcriteria
foreachwearmetal.Figure1isan
exampleofwhatfixedalarmsmight
looklike.
Thedrawbacktothistypeofalarming
techniqueisthatitdoesnotaccount
fordifferentcontributingfactors.
Lookingback
at
our
example
of
gearboxes,therearemanysizesand
shapesofgearboxes. Somegearboxes
arelightlyloadedandhaveaconstant
speed,whichwouldlenditselftoalow
wearrate.Suchagearboxmightbein
serioustroubleiftheironlevelwereto
reach200ppm.Ontheothersideof
thespectrum,youmayhavealow
speed,reversing,heavilyloaded
gearboxthathasneverhadlessthan
500ppmofironinitsoil.
Thelubricationmethodcanhavea
largeimpact
on
wear
metal
levels
as
well.Manygearboxesaresplash
lubricatedwithsmalloillevelsystems.
Thissituationwouldrevealasteady
increaseinwearmetallevelsand
causeafalsepositivereadingwhenthe
levelbroachesthefixedalarm.Other
gearboxesmightbelubricatedbya
filteredcirculatingsystem,wherewear
particlesareremovedbyfiltrationas
rapidlyastheyaregenerated.Inthis
case,thewearmetaltrendwouldbe
flat,andasignificantchangecould
occurwithoutsurpassingthefixed
alarm.Such
an
exception
would
likely
bemissedbyafixedlimitsystem.
Hydraulic Gearbox DieselEngine GasolineEngine Transmission Differential
Iron
75
300
150
150
300
1000
Chromium 5 N/A 25 25 10 N/A
Lead 20 N/A 50 150 50 N/A
Copper 75 250 50 75 400 250
Tin 10 250 25 40 20 250
Aluminum 25 250 30 40 50 250
Nickel 5 N/A 10 15 20 N/A
Figure1 | Anexampleoffixedalarms
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Understanding Alarm Levels
Trend Analysis
Trendanalysisallowsthedevelopment
ofapatternofbehaviorforaparticular
unit.Ifthesamplingtechniqueand
intervals
are
consistent,
regular
monitoringofthewearmetallevels
willalsohighlightthechangesinthe
wearrate.Thishelpstoaccountfor
manyofthevariableswithinthe
equipmentgroup. Anuncharacteristic
increaseiniron,asseeninFigure2,
wouldindicate
achange
in
the
wear
rate.
Manytechniquescanbeappliedto
evaluatingtrenddata,suchas
averages,standarddeviations,and
linear
regression.
All
are
intended
to
identifyaconditionthat
isnotnormalinrelationtothe
machinespastbehavior.Whatis
missinghereisidentifyingwhatis
normalforthatmachinetype.Isit
normalforagearboxtogeneratethis
levelof
iron?
100
80
60
40
20
0
10/01/12
11/02/ 12 12/07/12 01/05/13
Figure2 | Anexampleoffixedalarms.
Thisgraphrepresentstheamountofiron
presentinagivensample. Theyellowline
representsthemarginal,therediscritical
andtheblueshowstherisinglevelofiron
overaperiodoftime.
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Understanding Alarm Levels
Family Analysis
Familyanalysisisatechniquethat
comparesthewearmetallevelsof
groupsofsimilaroridentical
equipment
to
identify
what
is
a
usual
ortypicalpattern.
Equipmentisgroupedtogetherby
family. Afamilymayconsistof
identicalequipmentlocatedinmany
plants,suchasGEFrame7turbinesin
manypower
plants
across
the
country.
Youmightalsogroupequipment
togetherbasedonload,size,
lubricationtype,andoperating
parameters,suchasagroupof
agitatorsatachemicalplant.Thewear
metaldataisthenevaluatedasa
whole.The
data
for
each
machine
is
thencomparedtothefamilyto
evaluateitswearrate.
Asanexample,letssaythatwehavea
familyof50motorbearingsatasteel
mill.Theaveragetinreadingis7ppm
with90%ofthebearingsreadingless
than10ppm.Itwouldthenbesafeto
assumethatitisnormalforthese
bearings
to
have
less
than
10
ppm
tin
intheiroil.Ifoneofthebearingswere
foundtohave35ppmoftin,itwould
besafetosaythatitswearrateis
abnormal. Aneffortcouldthenbe
initiatedtodeterminethecauseofthe
higherwearrateandcorrectthe
problem.The
problem
could
be
detected,identified,andresolved
beforeanydamageoccurs.Ultimately,
thisefforthelpedtoavoidpremature
failureandanycostthatmighthave
beenincurredifthebearinghadtobe
replaced.
Familyanalysistechniquescanhavea
significantimpactonbothlargeand
smallprograms.Alargecompanycould
usesuchaprogramtomonitorlarge
fleetsofsimilarequipmentamong
theirplants,aswellastobenchmark
performanceofindividualplants.
Companieswithlessequipmentcan
comparetheirwearratesto
equipment
in
many
other
plants
and
takeadvantageofthelab'svast
databaseofequipmentdata.
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About TESTOIL
TESTOILisafullserviceoiltesting
laboratoryownedbyInsightServices. Since
1988thelaboratoryhasbeenprovidingfast
andreliableoilanalysisresultsacrossall
industriesthroughouttheAmericas.
Thefirmscomprehensiverangeofoil
analysisservicesassistsreliabilityengineers
withconditionmonitoringandidentification
ofmachinewear.
TESTOILemploys
asophisticated
diagnostic
technologythatassiststheirMachine
ConditionAnalystsinmakingequipment
andlubricationconditionassessments.
Contact
Us
Call: 2162512510
Email: [email protected]
Website: www.testoil.com
Tweetusat: @TESTOILanalysis