monitoring and alarming wear metals

7/26/2019 Monitoring and Alarming Wear Metals

1/8

Alarming

Monitoring

Wear Metals


2/8

Table Of Contents

WhatAlarmLevelsMeanforMachineWear ............................................................................................................................................. 3

UnderstandingAlarmLevels....................................................................................................................................................................... 4

BlendingTheTechniques ............................................................................................................................................................................ 7

AboutTESTOIL............................................................................................................................................................................................. 8

ContactUs................................................................................................................................................................................................... 8


3/8

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.


4/8

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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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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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.


7/8


8/8

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

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