Metal Samples MS1000 Bedienungsanleitung
MS1000
Corrosion Meter
Owner’s Manual
Metal Samples
A Division of Alabama Specialty Products, Inc.
152 Metal Samples Rd., Munford, AL 36268
Phone: (256) 358-4202 Fax: (256) 358-4515
Table of Contents
I. Introduction .....................................................................1
A. Background ...................................................................1
B. InstrumentCapabilities ...................................................2
C. ApplicationsfortheMS1000 .........................................6
II. MS1000Specifications and Features ..............................7
III. MS1000Operation ...........................................................9
A. Test Readings ................................................................9
B. DataAcquisition .............................................................9
1. InstantaneousCorrosionRateMeasurements ............9
2. ZRAandEPRMeasurements .................................10
C. Electrode Installation, ReplacementandCare ...............10
D. CorrectingforLowSolutionConductivity Effects.......... 11
IV. UNSConstantTable.......................................................14
V. Maintenance ...................................................................16
VI. Troubleshooting ..............................................................16
VII. ReplacementParts .........................................................18
VIII.Warranty ........................................................................20
IX. References......................................................................21
MS1000 manual - rev. 15.12
I. Introduction
A. Background
TheMS1000isaportable,hand-held,battery-poweredcorrosion
meter. Thisversatileinstrumentmeasurestheinstantaneouscorrosion
ratewiththe LinearPolarizationResistance(LPR) technique. Italso
measuresthecurrentflowingbetweenelectrodes intheshort-circuited
conditionwithahighprecisionzeroresistanceammeter(ZRA). The
MS1000cananalyze two-electrodelinearpolarizationresistanceor
galvanictypeprobes.
Theprincipleuse ofthisinstrument istomeasurecorrosion ratesunder
variousconditionsintheplant,field,orlab.Inadditiontousingthis
instrumenttomonitor corrosionrates,corrosionengineers canalsouse
theMS1000to monitorinhibitoreffectiveness, identityprocessupsets,
identifylocalizedcorrosionevents,andevaluatecorrectiveactionsin
realtime. Thesemeasurements areveryimportantsince achangeinthe
processconditionscanleadto dramatic changes intheobserved
corrosionrate.
1
B. Instrument Capabilities
Instantaneous Corrosion Rate Measurements
Instantaneouscorrosionrate measurementsaremade withthelinear
polarizationresistance(LPR)technique. Thistechnique isareliable
electrochemicalprocedurebased onprinciplesoutlinedinASTMG59
StandardPracticeforConductingPotentiodynamicPolarizationResis-
tanceMeasurements.1Anexcellenttechnicalreviewofthistechniqueis
givenelsewherebyMansfeld.2,3
Thedeterminationof a corrosionratefromthe parameters measured
withcorrosionprobesdependsonFaraday’slaw. Themassloss,
current,potential,andchanges inthesevariablesareconverted intoa
corrosionrate. ASTMG102StandardPractice for Calculation of
CorrosionRatesandRelatedInformationfrom ElectrochemicalMea-
surementsprovides allnecessaryinformationforthe directcalculationof
thecorrosionrate.4
ThemethodusedbytheMS1000 for calculating the corrosionrateisas
follows. Alow amplitudedcvoltageisapplied across theelectrodes
andthenthe resultingcurrent,normalized tocurrentdensity, ismea-
sured. Thevoltageis heldconstantforthirty secondsbeforemeasuring
thecurrent sothat anycapacitanceinthe oxidelayerwillbe fully
charged. Thepolarityofthe applied voltage isthenchangedandthe
measurementcycleis repeated. Polarityisreversedto minimizepoten-
tialerrorsdue topossibleelectrodedissimilaritiesorchangesin the
opencircuitpotentialoftheelectrodesduringthemeasurement.
Thepolarizationresistance,Rp, ofthecorrodingelectrodes is calcu-
latedfromtheslope of thepotential-currentdensityplot. Rpisdefined
as:
Rp=E
i
2
where Eis thepolarizationfrom theopencircuitpotential ofthe
electrodesandiisthemeasuredcurrentdensityat E.Sternand
Gearyshowedthat thereisalinear relationship betweenpotentialand
appliedcurrentatpotentialsonlyslightlyremovedfromthecorrosion
potential.1Basedonthe kineticsofelectrochemicalreactions and
conceptsofmixedpotentialtheory,asdiscussed byWagnerandTraud,
anequationwas derivedwhichrelatedthe polarizationresistancetothe
corrosioncurrentdensity,icorr.6Thecorrosion currentdensityiscalcu-
latedas:
whereßaandßc aretheanodicandcathodicTafelconstants (ie., the
slopesofthe anodicandcathodicpolarization curvesintheTafel
region).
The instantaneouscorrosionrate inmilsperyear (mpy)isdetermined
fromicorr withthefollowingequation:
icorr =2.303Rp(ßa+ ßc)
ßaßc
whereEWis theequivalentweight, Kisaconstant forunitsconversion,
and isthedensity. Theequivalentweightdepends upon the composi-
tionofthealloy. Guidelinesfordeterminingtheequivalentweightare
giveninASTMG102.4
Notethatthis instrument hasbeendesignedto calculatethecorrosion
rateofcarbonsteel and commongradesofstainlesssteel in milsper
year. Inother words, the programmedvaluesoftheTafelslopes,
equivalentweight,anddensityaretypical forcarbonsteelandcommon
gradesofstainlesssteel. Multiplicationfactorsfor copper,admiralty
brass,andleadare includedonthefrontpanel of theinstrument.
COR(mpy) =icorr • EW • K
3
Theinstrumentisprogrammedforelectrodeswithsurfaceareas offive
cm2. Multiplicationfactorsarealsoincludedforflushmountelectrodes
withsurfaceareasof0.5cm2.
Zero Resistance Ammeter (ZRA) and Equivalent Pitting Rate
Ahighprecisionzeroresistanceammeterisusedformonitoring the
short-circuitcurrentbetweenelectrodes. Thistotalcurrent flowing
betweentheelectrodes intheshort-circuitedcondition ismonitored.
Thecurrentis displayedinmicroamps. Thezero resistanceammeter
(ZRA)functionmayalsobeusedtomonitorthe galvaniccurrent
betweenelectrodesof differentalloysorthe areaeffectofgalvanic
corrosion.
Generally,ifthemagnitudeoftheZRAreading dividedby2islessthan
thecorrosionrate, then pittingmaybeoccurring but thepitswillprob-
ablybeshallow andwide;however,pittingmaybe aseriousconcernif
theZRA/2 isgreaterthanthecorrosionrate.
Faraday’slaw may be used tocalculatethemassofmateriallostasa
resultof thelocalizedcorrosionasfollows:
W=[( ZRA)/n] • t • EW
F
whereWisthemassofthecorrodedmetal in grams, ( ZRA)/nis the
time-integratedZRAdivided by n,thenumber ofdaysofexposure,tis
thetime thecurrentisflowingin seconds,EWistheequivalentweight
aspreviouslydefined,andF istheFaraday constant, 96480Coulombs/
mol. Themassofthecorrodedmaterialmaybeusedto calculate a
4
corrosionrate,designatedasthe equivalent pitting rate, basedonthe
ZRA. Thisequivalentpittingrateisdefinedas:
whereEPRisthe equivalentpittingrateinmpy,K’isa constantfor
unitsconversion,Aisthe surface areaincm2, Wis the masslossin
grams, tisthetimeofexposureinseconds,and isthedensity of the
alloyingrams/cm3.
Additionaltechnicalinformationonthisinstrumenthasbeenpublishedin
theProceedingsofthe1994 InternationalWaterConference.7
EPR =K’ • W
A • t •
5
C. ApplicationsfortheMS1000
• Measuretheinstantaneous corrosionrateinaqueous solutions.
Forexample,thecontent anddosageofinhibitorsin water
treatmentfacilitiesandchemicalprocessplantscanbemonitored
andoptimized.
• Monitorthe actuallifetimeofplantequipment.Corrosion
monitoringprovidesdatathatmaybe combinedwithother forms
ofdatatoestimatethelifetimeofequipmentintheplant.
• Detectionoflocalizedcorrosion due toprocessconditionsor
upsets.
• Evaluatealternatematerials foraspecificpurpose. Optionfor
otheralloys,heat treatments,orfinishesmay beevaluatedand
comparedtotheperformance ofthespecificalloyconsidered.
• Analyzegalvanic probesandmeasurethegalvaniccurrent
betweenelectrodes. Areaeffects ingalvaniccorrosioncanalso
beinvestigated.
6
Inhaltsverzeichnis
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