amine plant sulphur-related corrosion
DESCRIPTION
Amine Plant Sulphur-Related CorrosionTRANSCRIPT
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AminePlantSulphurRelatedCorrosion
BenSpooner,P.EngAmine Experts Inc.
NACECalgarySectionElemental Sulfur Corrosion & its Mitigation
AmineExpertsInc.
Elemental Sulfur Corrosion&itsMitigation
October8th,2010Calgary,ABg y
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HowCorrosionOccurs:1Ionization
Mild Steel
e-Fe
e-
Fe+2
Fe Fe+2 + 2e-
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HowCorrosionOccurs:2
Mild Steel
e- e-e- e-e- e
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F +2Fe+2 Fe+2 Fe+2
l t t i i l ti electrons cannot survive in an aqueous solution -they hide in the metal, making it negatively charged (polarized) and eventually stopping the reaction(polarized), and eventually stopping the reaction unless
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HowCorrosionOccurs:3
Mild Steel
H
e- Fe+2H
He-
F +2 H+H+ H
th ti h i th t l i h
Fe+2Fe+2
H+H2
... the negative charge in the metal is somehow reduced- H+ ions can do this by reacting with e- to form hydrogeny g y g- if the circuit is completed in this way, corrosion will
continue until the system runs out of either Fe or H+
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HowCorrosionOccurs:4
Overall,thesituationis:Fe+2H+Fe2+ +H2
asH+ isoneofthereactants,thehigherits, gconcentration,thefasterthecorrosionreaction
the lower the pH, the greater the amount of H+ ionsthelowerthepH,thegreatertheamountofH ionsinsolution
a decrease of one pH unit increases the H+ adecreaseofonepHunitincreasestheHconcentrationbyafactoroften
this is why corrosion is so severe in acid conditionsthisiswhycorrosionissosevereinacidconditions
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BasicCorrosionEquationsq
H2SattackFe+H2SFeS+2H0
ifH2Spartialpressureishighenough,FeSfilmformsaprotective layerprotectivelayer
CO attackCO2 attackFe+2H2CO3 Fe2+ +2HCO3 +2H0
iron carbonate film is not strong eno gh to protect metal ironcarbonatefilmisnotstrongenoughtoprotectmetalfromfurtherattack
mostlysolubley
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HowH2SProtects:1
withacidspresent,steelcatalysesthep , yformationofmolecularhydrogen
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HowH2SProtects:2
if H2S is present, the H-combination reaction is greatly reduced and H diffuses into the metalgreatly reduced and H diffuses into the metal until the FeS layer is formed
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HowH2SProtects:3
FeS scale slows corrosion and acts as a barrier to hydrogen penetration so that blistering mayto hydrogen penetration so that blistering may not occur
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ReasonsforCorrosion
acid contamination reduces pH acidcontaminationreducespH
amineloadingtoohigh
CO is present in large quantities CO2 ispresentinlargequantitieswilldissolveFeSfilm
high amine degradation levels highaminedegradationlevels
erosion(dirt)removesFeSlayerunit velocities are too highunitvelocitiesaretoohigh
gasorliquiddistributorsarefouledorincorrectlydesigneddesigned
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CorrosionCorrosionSymptoms
fouledsolution;coffeecolour
highfilterchangeoutfrequency
equipmentplugging
highFe,Mn,Cr,Niinsolvent
excessiveprobecorrosionrates
inspectionreports
equipmentfailure
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Corrosion H2S and other acidsCorrosion H2Sandotheracids
critical areas are at location of desorption or criticalareasareatlocationofdesorptionorevolutionofH2Sorotheracidgasses
gas evolution rate greatest in equipment where gasevolutionrategreatestinequipmentwheretemperatureishighest
equipment most prone to corrosion:equipmentmostpronetocorrosion: lean/richexchanger regeneratorbottoms reboiler associatedhotsidepiping
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Flow ObstructionFlowObstruction
Acid gas breakout
after flow obstruction
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Metal Attack
Gasket from LC Valve(pressure let-downvalve) prior to regenerator
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Regenerator C iCorrosion
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Acids condensing and dripping down from the bottom traydown from the bottom tray
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Non spray-metallized surfaceNon spray metallized surface
Spray-metallized surface
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Mackinawite or l t llno scale at all
P itPyriteScale
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PreventingCorrosiond l guidelines:
maximum rich amineloading:80%ofeq.acidgas/amine0 4 0 55 mol/mol0.4 0.55mol/mol
maximum leanamineloadings MEA,DGA0.1;DEA0.04;MDEA0.01mol/mol
maximum velocityof 1m/s(3ft/s) inexchangers
/ ( f / ) 2m/s(7ft/s)inpipes
filteroutsolids
t l h t t bl lt controlheatstablesalts
properregeneration
postweldheattreatallaminerelatedvessels
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Cool end of L/Rof L/R Exchanger
LeanSide Build-upp
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Classic h li hshoe polishdeposit in exchanger
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CorrosionCase Fouling
Packingandsupportdamageg pp g heavyhydrocarbonfouledpackingofahighpressure(2200psi)recyclegasscrubber
subsequentmaldistributionofaminecausedlocalizedhighloading(0.8 0.9mol/mol)
l li d i f l ll i d localizedcorrosionofcolumnwallincreasedfoulingandmaldistribution
support plate of packing was almost entirely gone supportplateofpackingwasalmostentirelygone columnwalllost3 6mmthicknessatseveralplacesinonly18months
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Lean MDEALean MDEA
Note clarityNote clarityand absence ofabsence of solids
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Solution has turned green / black and contains many suspendedand contains many suspended solids after H2S contact
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Corrosion Case DesignCorrosionCase Design
Local absorber wall corrosionLocalabsorberwallcorrosion thewallwascorrodedoppositetheabsorbergasinlet (180)inlet(180 )
aminefromthedowncomerofthelasttraywasentrainedagainstthewallg
extendingthedowncomertotheliquidleveldowninthecolumnsolvedtheproblemp
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Corrosion - Design
Corrosion zone
Amine raining down from bottomAmine raining down from bottom tray
Gas Inlet
Entrained amine dropletsin gas impinge on vessel surfacein gas impinge on vessel surface
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Ripple type erosion from high vapour flow impinging on liquid raining downflow impinging on liquid raining down from the chimney tray of an absorber
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HIC on absorber faceopposite feed gas pointopposite feed gas point
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Hydrogen DamageHydrogenDamage
H2 inducedcracking HIC2 g blisteringandcrackingalonginclusionsthatoccursinlowerstrengthsteelssubjectedtohighH2g j g 2concentrations
atomicHformedbyFecorrosionreactions prevention:
useofsteelwithlowlevelsofimpurities modifyingtheenvironmenttoreduceHcharging useofsurfacecoatingsandeffectiveinhibitors
ll bl f f h l f generally,blisteringisafunctionofthequalityofworkmanshipinvesselconstruction
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HIC in absorberHIC in absorber
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Hydrogen induced blisteringblistering
in amine flash drumdrum
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Galvanic CorrosionGalvanicCorrosion
twodissimilarmetalscoupledtogetherinaconductingelectrolyte
theelectrochemicalpotentialbetweenthetwometalscausestheleastresistantmetaltocorrode carbonsteelboltswouldpreferentiallycorrodeoverstainlesssteeltraystheyareholdingdown(sacrificialanode)
reverseisnotasseriousbecauseofthelargeareaoftheanode(tray)versusthesmallareaofcathode(bolt)
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410 SS bolts holding downg316 SS trays
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316SS valvesd band carbon
steel tray deck
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Pitting CorrosionPittingCorrosion
highly localized and intense corrosionhighlylocalizedandintensecorrosion resultsinrapidanddestructivepenetrationatrelativelyfewspots
equipmentfailuresassociatedwithpittingarequiteoftensuddenandunexpected
promotedbychloridesandstagnantareas
carbonsteelismoreresistanttopittingcorrosionthanstainlesssteel
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CO2 pitting in regeneratorbottom note highlylocalized attack zones
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Erosion CorrosionErosionCorrosion
exposureoffreshmetaltoacidgasduetoabrasionofanyprotectivecoatingorfilm
excessiveliquidorvapourvelocitiesaretheprimarycause
aggravatedbysolidsinsolution
systemlayoutisimportant(impingementplates,)elbows,inletorientations,etc.)
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ErosionErosion
Note attack at non-amine wetted surface
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CorrosionCoupons theoldestandsimplestmonitoringdevice
strips of system metallurgy inserted into the stripsofsystemmetallurgyinsertedintotheprocessstreamandremovedafterasetperiodoftime for studytimeforstudy
determinesaverage corrosionrateovertheperiodofexposurep p
measurethecouponbeforeandafterexposureforweightlossg
corrosionratedeterminedfromweightloss,initialsurfaceareaandtime
atleast30daysexposureneeded
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Untreated Treated
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Ultrasonic MeasurementUltrasonicMeasurement
specialized equipment is requiredspecializedequipmentisrequired
almostexclusivelyaninspectiontool AScans provide a simple depth measurement fromA Scans provideasimpledepthmeasurementfromtheexteriorsurfaceofapipeorvesseltothenextinterfacethatreflectssoundwaves(generallymeasureswall thickness but can be fooled by mid wall flaws)wallthickness,butcanbefooledbymidwallflaws)
BScans producemorepowerfulcrosssectionalimagessimilartoxraysg y
CScans producea3dimensionalviewofasurfaceusingcomplexandexpensiveequipment(rarelyusedinplant applications)plantapplications)
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Blistering as viewedviewedby C-scan
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Chemical AnalysisChemicalAnalysis
appearencepp
isthemonitoringofthechemicalcompositionorcharacteristicsoftheprocessfluids
sincecorrosionisanelectrochemicalphenomenon,chemicalanalysiscanbeausefulindicatorofthecorrosivityoftheprocess
testforFe,Mn,Cr,Ni
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Visual InspectionVisualInspection rarelypracticalinaworkingprocessplant,however whenever an opportunity presents itselfhowever,wheneveranopportunitypresentsitself,weMUST takeadvantage
only through direct visual inspection can we be onlythroughdirectvisualinspectioncanwebeabsolutelycertainoftheconditionofaprocessunit
duringturnarounds,visualinspectionsareimportanttoolsto:
verifytheresultsofonlinemonitoring choosenewlocationsformonitoring assesspreviousrepairwork
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Corrosion SummaryCorrosionSummary
corrosion is primarily caused by liberation of acidcorrosionisprimarilycausedbyliberationofacidgasesandtheirsubsequentcontactwithwarm,wetsteel
anythingthataffectsthetemperature,pressureorvelocityofanaminestreamcanresultinacidgasbreakout
generally,aminewettedsurfacesexhibitlowerd h d fcorrosivetendenciesthannonwettedsurfaces
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Canyouguesstheaminelevelinthis vessel?thisvessel?