AminePlantSulphurRelatedCorrosion

BenSpooner,P.EngAmine Experts Inc.

NACECalgarySectionElemental Sulfur Corrosion & its Mitigation

AmineExpertsInc.

Elemental Sulfur Corrosion&itsMitigation

October8th,2010Calgary,ABg y

HowCorrosionOccurs:1Ionization

Mild Steel

e-Fe

e-

Fe+2

Fe Fe+2 + 2e-

HowCorrosionOccurs:2

Mild Steel

e- e-e- e-e- e

-

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

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+

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

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

HowH2SProtects:1

withacidspresent,steelcatalysesthep , yformationofmolecularhydrogen

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

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

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

CorrosionCorrosionSymptoms

fouledsolution;coffeecolour

highfilterchangeoutfrequency

equipmentplugging

highFe,Mn,Cr,Niinsolvent

excessiveprobecorrosionrates

inspectionreports

equipmentfailure

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

Flow ObstructionFlowObstruction

Acid gas breakout

after flow obstruction

Metal Attack

Gasket from LC Valve(pressure let-downvalve) prior to regenerator

Regenerator C iCorrosion

Acids condensing and dripping down from the bottom traydown from the bottom tray

Non spray-metallized surfaceNon spray metallized surface

Spray-metallized surface

Mackinawite or l t llno scale at all

P itPyriteScale

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

Cool end of L/Rof L/R Exchanger

LeanSide Build-upp

Classic h li hshoe polishdeposit in exchanger

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

Lean MDEALean MDEA

Note clarityNote clarityand absence ofabsence of solids

Solution has turned green / black and contains many suspendedand contains many suspended solids after H2S contact

Corrosion Case DesignCorrosionCase Design

Local absorber wall corrosionLocalabsorberwallcorrosion thewallwascorrodedoppositetheabsorbergasinlet (180)inlet(180 )

aminefromthedowncomerofthelasttraywasentrainedagainstthewallg

extendingthedowncomertotheliquidleveldowninthecolumnsolvedtheproblemp

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

Ripple type erosion from high vapour flow impinging on liquid raining downflow impinging on liquid raining down from the chimney tray of an absorber

HIC on absorber faceopposite feed gas pointopposite feed gas point

Hydrogen DamageHydrogenDamage

H2 inducedcracking HIC2 g blisteringandcrackingalonginclusionsthatoccursinlowerstrengthsteelssubjectedtohighH2g j g 2concentrations

atomicHformedbyFecorrosionreactions prevention:

useofsteelwithlowlevelsofimpurities modifyingtheenvironmenttoreduceHcharging useofsurfacecoatingsandeffectiveinhibitors

ll bl f f h l f generally,blisteringisafunctionofthequalityofworkmanshipinvesselconstruction

HIC in absorberHIC in absorber

Hydrogen induced blisteringblistering

in amine flash drumdrum

Galvanic CorrosionGalvanicCorrosion

twodissimilarmetalscoupledtogetherinaconductingelectrolyte

theelectrochemicalpotentialbetweenthetwometalscausestheleastresistantmetaltocorrode carbonsteelboltswouldpreferentiallycorrodeoverstainlesssteeltraystheyareholdingdown(sacrificialanode)

reverseisnotasseriousbecauseofthelargeareaoftheanode(tray)versusthesmallareaofcathode(bolt)

410 SS bolts holding downg316 SS trays

316SS valvesd band carbon

steel tray deck

Pitting CorrosionPittingCorrosion

highly localized and intense corrosionhighlylocalizedandintensecorrosion resultsinrapidanddestructivepenetrationatrelativelyfewspots

equipmentfailuresassociatedwithpittingarequiteoftensuddenandunexpected

promotedbychloridesandstagnantareas

carbonsteelismoreresistanttopittingcorrosionthanstainlesssteel

CO2 pitting in regeneratorbottom note highlylocalized attack zones

Erosion CorrosionErosionCorrosion

exposureoffreshmetaltoacidgasduetoabrasionofanyprotectivecoatingorfilm

excessiveliquidorvapourvelocitiesaretheprimarycause

aggravatedbysolidsinsolution

systemlayoutisimportant(impingementplates,)elbows,inletorientations,etc.)

ErosionErosion

Note attack at non-amine wetted surface

CorrosionCoupons theoldestandsimplestmonitoringdevice

strips of system metallurgy inserted into the stripsofsystemmetallurgyinsertedintotheprocessstreamandremovedafterasetperiodoftime for studytimeforstudy

determinesaverage corrosionrateovertheperiodofexposurep p

measurethecouponbeforeandafterexposureforweightlossg

corrosionratedeterminedfromweightloss,initialsurfaceareaandtime

atleast30daysexposureneeded

Untreated Treated

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)

Blistering as viewedviewedby C-scan

Chemical AnalysisChemicalAnalysis

appearencepp

isthemonitoringofthechemicalcompositionorcharacteristicsoftheprocessfluids

sincecorrosionisanelectrochemicalphenomenon,chemicalanalysiscanbeausefulindicatorofthecorrosivityoftheprocess

testforFe,Mn,Cr,Ni

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

Corrosion SummaryCorrosionSummary

corrosion is primarily caused by liberation of acidcorrosionisprimarilycausedbyliberationofacidgasesandtheirsubsequentcontactwithwarm,wetsteel

anythingthataffectsthetemperature,pressureorvelocityofanaminestreamcanresultinacidgasbreakout

generally,aminewettedsurfacesexhibitlowerd h d fcorrosivetendenciesthannonwettedsurfaces

Canyouguesstheaminelevelinthis vessel?thisvessel?