Understanding the corrosion Understanding the corrosion environmentenvironment
TeachTeach--ininThe CorrosionThe Corrosion
Any method be made more effectiveAny method be made more effective……
CouponsCouponsOnline MonitorsOnline MonitorsInhibition programsInhibition programs
Different methods for corrosion controlDifferent methods for corrosion control
……When you understand the When you understand the effect of the corrosion effect of the corrosion
environmentenvironment
Corrosion rates vary with Corrosion rates vary with process conditionsprocess conditions
It helps to know the effect It helps to know the effect of variations in the fieldof variations in the field
To interpret coupon To interpret coupon and monitor dataand monitor data……
Wait for a failureWait for a failure……??Rely on past experience?Rely on past experience?
To locate where To locate where to place sensors & to place sensors & couponscoupons……
Tell you what has already Tell you what has already happened, happened, notnot what will what will
happenhappen
CouponsCouponsOnline MonitorsOnline Monitors
Protective ScalePassive Film
Active Corrosion (dissolution)
pH
Understand what’s happening in your systemUnderstand what’s happening in your system
Determine the rate limiting redox processesDetermine the rate limiting redox processes
Rate-limiting cathodic process
Activation controlled
Passive region
Determine pitting potential and max growth rateDetermine pitting potential and max growth rate
PittingNo Pitting
Test Corrective ActionsTest Corrective Actions•• Determine optimum pHDetermine optimum pH•• Screen alloys and inhibitorsScreen alloys and inhibitors•• Assess process changesAssess process changes
Focus Lab workFocus Lab work
Eliminate potential problems Eliminate potential problems before they occurbefore they occur
Pro-active AnalysisPro-active Analysis
The Corrosion AnalyzerThe Corrosion Analyzer
Mechanistically-based software toolMechanisticallyMechanistically--based software toolbased software tool
Tool for understanding the corrosion environment
SpeciationKinetics of uniform corrosion
Partial anodic and cathodic processes
Transport propertiesRepassivation
SpeciationSpeciationKinetics of uniform corrosionKinetics of uniform corrosion
Partial anodic and cathodic Partial anodic and cathodic processesprocesses
Transport propertiesTransport propertiesRepassivationRepassivation
Complete speciation model for complex mixtures
Phase and chemical reaction equilibria
Accurate pH prediction
Redox chemistry
Comprehensive coverage of industrial chemical and petroleum systems
Complete speciation model for complex Complete speciation model for complex mixturesmixtures
Phase and chemical reaction equilibriaPhase and chemical reaction equilibria
Accurate pH predictionAccurate pH prediction
Redox chemistryRedox chemistry
Comprehensive coverage of industrial Comprehensive coverage of industrial chemical and petroleum systemschemical and petroleum systems
The Corrosion AnalyzerThe Corrosion AnalyzerBased on the OLI Engine
ThermophysicalThermophysical properties predictionproperties prediction
Phenomenological and unique aqueous Phenomenological and unique aqueous process models including kinetics and process models including kinetics and transporttransport
““OutOut--ofof--thethe--boxbox”” solution and technical solution and technical supportsupport
The Corrosion AnalyzerThe Corrosion AnalyzerBased on the OLI Engine
What It Does…What It DoesWhat It Does……
Predict metal dissolution regime, passive films, and surface depositsPredict metal dissolution regime, passive films, Predict metal dissolution regime, passive films, and surface depositsand surface depositsPredict uniform corrosion rates and the potential for pitting corrosionGenerate real solution stability (Pourbaix) DiagramsProduce theoretical polarization curves
Predict uniform corrosion Predict uniform corrosion rates and the potential for rates and the potential for pitting corrosionpitting corrosionGenerate real solution Generate real solution stability (Pourbaix) stability (Pourbaix) DiagramsDiagramsProduce theoretical Produce theoretical polarization curvespolarization curves
The Corrosion AnalyzerThe Corrosion Analyzer
So you can gain insight on …So you can gain insight on So you can gain insight on ……
Corrosion mechanisms Rate-limiting partial processes for your operating conditionsEffects of process and materials changes
Corrosion mechanisms Corrosion mechanisms RateRate--limiting partial processes for your operating limiting partial processes for your operating conditionsconditionsEffects of process and materials changesEffects of process and materials changes
ThereforeFocusing lab time Reducing risky plant/field testingManaging design, operation, and maintenance
ThereforeThereforeFocusing lab time Focusing lab time Reducing risky plant/field Reducing risky plant/field testingtestingManaging design, operation, Managing design, operation, and maintenanceand maintenance
The Corrosion AnalyzerThe Corrosion Analyzer
Today’s seminar “Hands-on” and “How-To”
Using example problems
Examining plots and
diagrams
Understanding the basis of
the predictions
Today’s seminar “HandsHands--onon”” and and ““HowHow--ToTo””
Using example problemsUsing example problems
Examining plots and Examining plots and
diagramsdiagrams
Understanding the basis ofUnderstanding the basis of
the predictionsthe predictions
Perform “Single point” calculationsConstruct / interpret real solution Pourbaix DiagramsCalculate corrosion rates
Evaluate the effects of pH, T, comp / flow
Evaluate polarization curvesGain insight to corrosion mechanismsSee rate limiting steps Can I read them? Can I trust them?
Determine the likelihood of pitting to occur
For your actual field or lab conditions
Perform Perform ““Single pointSingle point”” calculationscalculationsConstruct / interpret real solution Pourbaix DiagramsConstruct / interpret real solution Pourbaix DiagramsCalculate corrosion rates Calculate corrosion rates
Evaluate the effects of pH, T, comp / flowEvaluate the effects of pH, T, comp / flow
Evaluate polarization curvesGain insight to corrosion mechanismsSee rate limiting steps Can I read them? Can I trust them?
Determine the likelihood of pitting to occur
For your actual field or lab conditionsFor your actual field or lab conditions
Today’s SeminarToday’s Seminar
Gas Condensate CorrosionGas Condensate Corrosion
ScopeScopeGas condensates from alkanolamine gas Gas condensates from alkanolamine gas sweetening plants can be highly corrosive.sweetening plants can be highly corrosive.
PurposePurposeDiethanolamine is used to neutralize Diethanolamine is used to neutralize (sweeten) a natural gas stream. This removes (sweeten) a natural gas stream. This removes carbon dioxide and hydrogen sulfide. The off carbon dioxide and hydrogen sulfide. The off gas from the regeneration is highly acidic and gas from the regeneration is highly acidic and corrosivecorrosive
Gas Condensate CorrosionGas Condensate Corrosion
ObjectivesObjectivesDetermine the dew point of the acid gasDetermine the dew point of the acid gasRemove the condensed phase and perform Remove the condensed phase and perform corrosion rate calculationscorrosion rate calculationsMitigate the corrosionMitigate the corrosion
Acid Gas ConcentrationsAcid Gas Concentrations
100 moles100 molesAmountAmount1.2 Atm.1.2 Atm.PressurePressure38 38 ooCCTemperatureTemperature0.030.03PropanePropane0.030.03EthaneEthane0.500.50MethaneMethane16.616.6HH22SS0.020.02NN22
77.477.4COCO22
5.425.42HH22OOConcentration (mole %)Concentration (mole %)SpeciesSpecies
Corrosion Rates: Flow Corrosion Rates: Flow ConditionsConditions
Flow conditions have a direct effect on Flow conditions have a direct effect on massmass--transfertransfer
StaticStaticPipe flowPipe flowRotating diskRotating diskRotating cylinderRotating cylinderComplete agitationComplete agitation
Carbon Steel Corrosion @ Dew PointCarbon Steel Corrosion @ Dew Point
H2CO3(aq)= ½ H+ + HCO3- - e
HS-= ½ H2 + S2- - e
H+= ½ H2 - e
H2S(aq)= ½ H2 + HS- - e
Corrosion Rate = 0.7 mm/yr
Corrosion Potential = -0.43 V
Repassivation Potential = > 2 V
Current Density = 60.5 μA/cm2
MitigationMitigation
Adjusting solution chemistryAdjusting solution chemistryTemperature profilingTemperature profilingAlloy screeningAlloy screeningCathodic protectionCathodic protection
Adjusting the Solution Adjusting the Solution ChemistryChemistry
Changing operating pHChanging operating pHAdd acid or baseAdd acid or base
Screening AlloysScreening Alloys
Select an alloy that has a preferential Select an alloy that has a preferential corrosion ratecorrosion rate
13% chromium13% chromium304 Stainless304 Stainless
13 % Cr Steel Corrosion @ Dew Point13 % Cr Steel Corrosion @ Dew Point
H2CO3(aq)= ½ H+ + HCO3- - e
HS-= ½ H2 + S2- - e
Corrosion Rate = 0.06 mm/yr
Corrosion Potential = -0.32 V
Repassivation Potential = > 2 V
Current Density = 5.7 μA/cm2
304 Stainless Steel Corrosion @ Dew Point304 Stainless Steel Corrosion @ Dew Point
Corrosion Rate = 0.0036 mm/yr
Corrosion Potential = -0.15 V
Repassivation Potential = > 2 V
Current Density = 0.3 μA/cm2
304 Stainless Steel Stability @ Dew Point304 Stainless Steel Stability @ Dew Point
Passivation is possible due to Cr2O3
Why Iron RustsWhy Iron RustsExplaining common observations Explaining common observations
using Stability Diagramsusing Stability Diagrams
BasicsBasicsIron is inherently unstable in water & oxidizes via the Iron is inherently unstable in water & oxidizes via the following reactions to form rustfollowing reactions to form rust
Its severity depends on (among others)Its severity depends on (among others)Conditions (T/P), Conditions (T/P), Composition, Composition, pH, and pH, and oxidation potentialoxidation potential
These four can be plotted on a single chart called a These four can be plotted on a single chart called a stability diagramstability diagram
232
3
22
23)(3
3
32333
HOHFeOHFe
eFeFe
OHHeOH
o
o
+→+
+→
+→+−+
−−
Explaining the EH-pH diagram using Fe, showing solid and dissolved species over range of pH’s and oxidation potentials
H2O is oxidized to O2 and H+
H2O is reduced to H2 and OH-
Elemental iron, Fe(0)o, is stable and will not corrode in this region
H2O is stable and deaerated
H2O is stable and aeratedFe2O3 reduces and dissolves in water
Fe(II) oxidizes and precipitates as Fe2O3
Elemental iron, Fe(0) oxidizes to Fe(II) in the presence of water
FeO(OH), rust is stable in water at moderate to high pH’s
White area is region of iron corrosion
Water Oxidation Line
Water Reduction LineFe3O4 coats the iron surface, protecting it from corrosion
Fe(III)3+ is the dominant ion
Fe(II)2+ is the dominant ion
Elemental iron (gray region) corrodes in water to form one of several phases, depending on pH. At ~9 pH and lower, water oxidizes Fe0 to Fe+2 which dissolves in water (white region of the plot). As the oxidation potential increases (high dissolved O2) Fe+2 precipitates as FeOOH, or rust (green region). The lower the pH, the thicker the white region and the greater driving force for corrosionAt higher pH (10-11), Fe0 forms Fe3O4, a stable solid that precipitates on the iron surface, protecting it from further attack.
H2O is oxidized to O2 and H+
H2O is stable and aeratedWater Oxidation Line
−+ ++→ eHOOH 2221
22
H2O is reduced to H2 and OH-
H2O is stable and deaerated
Water Reduction Line
+− +→+ OHHeOH 22 21
Q: We all know O2 is bad…But how much is bad?
Pure water is here…No air, no acid, no base
0.1 ppT H2
0.1 ppT O2
0.1 ppb H2
3 ppb O2
10 ppm O2
0.1ppm H2
500 ppm O2
80 ppm H2
Elemental Iron (Feo)
++
−+
+−
++→+
+→
+→+
OHHFeOHFeeFeFe
OHHeOH
o
o
222
222
22
2
222
Iron and water react because they are not stable together
Region of instabilityThe reaction generates H2, which puts the EH near the bottom line
The reaction generates 2OH-, which increases the pH
Initial ConditionsDI water, no Feo
7pH, 0.4V
Final Conditions1 ppm Feo added9.38pH, 0.5V
0.9 ppb Feo
7.07pH, -0.27V
0.1 ppm Feo
8.48pH, -0.42V
The reaction ends within the Fe3O4 region. Fe3O4 is a solid that passivates the iron surface protecting it from active corrosion
1.4 g Fe3O4 ppts from 1 Feo
Fe3O4 precipitates when 0.3 mg/l Feo has reactedTh
e pp
tpoi
nt li
nes
up
with
the
stab
ility
cur
ve
Overlaying the Fe3O4 mass on the diagram – once the pH reached 9, Fe3O4 began to precipitate
The EH and pH does not change as Feo reacts with aerated water
If a constant source of O2 is present, then the EH and pH do notchange, and we are stuck in the rust region
Corrosion in SeawaterCorrosion in Seawater
ScopeScopeMetals used for handling sea water face both general Metals used for handling sea water face both general and localized corrosion.and localized corrosion.Various grades of stainless steels have been used to Various grades of stainless steels have been used to mitigate the problems.mitigate the problems.Stainless steels owe their corrosion resistance to a Stainless steels owe their corrosion resistance to a thin adherent film of oxides on their surface. thin adherent film of oxides on their surface. Disruption of the films can lead to localized corrosion Disruption of the films can lead to localized corrosion and premature failure.and premature failure.
Corrosion in SeawaterCorrosion in Seawater
PurposePurposeChlorine and oxygen in sea water can attack Chlorine and oxygen in sea water can attack the films used to passivate the steels.the films used to passivate the steels.The CorrosionAnalyzer will be used to model The CorrosionAnalyzer will be used to model the effects of chloride and oxygen on the the effects of chloride and oxygen on the rates of uniform corrosion and the possibility rates of uniform corrosion and the possibility of pitting on the surface of the metals.of pitting on the surface of the metals.
Corrosion in SeawaterCorrosion in Seawater
ObjectivesObjectivesReconcile a sea water sample for Reconcile a sea water sample for electroneutralityelectroneutralityReconcile a gas analysisReconcile a gas analysisCalculate uniform rates of corrosion forCalculate uniform rates of corrosion for•• 304 stainless steel304 stainless steel•• 316 stainless steel316 stainless steel•• S31254 stainless steelS31254 stainless steel
Corrosion in SeawaterCorrosion in Seawater
Objectives (continued)Objectives (continued)Determine the probability of pitting using the Determine the probability of pitting using the localized corrosion feature.localized corrosion feature.
Kinetic Model of General Kinetic Model of General Corrosion: MassCorrosion: Mass--TransferTransfer
All reactions take place on the All reactions take place on the metal surface.metal surface.Films are a diffusion barrier to Films are a diffusion barrier to corrosive speciescorrosive species
Reduce massReduce mass--transfertransfer--limited limited currents.currents.
MassMass--transfer from solution is transfer from solution is calculated from a concentrationcalculated from a concentration--dependent diffusion coefficient.dependent diffusion coefficient.
film
Metal
Surface
Solution
ChemistryChemistry
The rates of corrosion use a subset of the OLI The rates of corrosion use a subset of the OLI ChemistryChemistry
Neutral SpeciesNeutral Species•• HH--22O, OO, O22, CO, CO22, H, H--22S, NS, N22 and all inert gases, Cland all inert gases, Cl22, SO, SO22, S, Soo and and
NHNH33, organic molecules that do not undergo electrochemical , organic molecules that do not undergo electrochemical reactionsreactions
AnionsAnions•• OHOH--, , ClCl--, Br, Br--, I, I--, HCO, HCO33
--, CO, CO33--22, HS, HS--, S, S22--, SO, SO44
22--, HSO, HSO44--, SO, SO33
22--, , NONO22
--, NO, NO33--, MoO, MoO44
22--, CN, CN--, ClO, ClO44--, ClO, ClO33
--, , ClOClO--, acetate, formate, , acetate, formate, Cr(VI) anions, As(III) anions, P(V) anions, W(VI) anions, Cr(VI) anions, As(III) anions, P(V) anions, W(VI) anions, B(III) anions and B(III) anions and Si(IVSi(IV) anions.) anions.
ChemistryChemistry
CationsCations•• HH++, alkali metals, alkaline earth metals, Fe(II) , alkali metals, alkaline earth metals, Fe(II)
cations, Fe(III) cations, Al(III) cations, cations, Fe(III) cations, Al(III) cations, Cd(IICd(II) ) cations, cations, Sn(IISn(II) cations, Zn(II) cations, Cu(II) ) cations, Zn(II) cations, Cu(II) cations, cations, Pb(IIPb(II) cations and NH) cations and NH44
++..
Corrosion of 304 Stainless Steel in Corrosion of 304 Stainless Steel in Deaerated Sea WaterDeaerated Sea Water
LabAnalyzer used LabAnalyzer used to reconcile to reconcile electroneutralityelectroneutralityNaOH/HClNaOH/HCl Used Used to adjust pHto adjust pH
8.08.0pHpH25 25 ooCCTemperatuTemperatu
rere
150150HCOHCO33--
1 1 atmatm..PressurePressure
27502750SOSO44--22
400400CaCa+2+2
13001300MgMg+2+2
1070010700NaNa++
1900019000ClCl--
ConcentratiConcentration (mg/L)on (mg/L)
SpeciesSpecies
Screening ConsiderationsScreening Considerations
Some alloys do not perform well in Some alloys do not perform well in seawaterseawaterWe will evaluate 3 stainless steelsWe will evaluate 3 stainless steels
Uniform corrosion ratesUniform corrosion ratesPitting possibilityPitting possibility
Considering both deaerated and aerated Considering both deaerated and aerated conditionsconditions
Corrosion of 304 Stainless Steel in Corrosion of 304 Stainless Steel in Deaerated Sea WaterDeaerated Sea Water
300 years to lose 1 mm of metal
.0033 mm/yr @ 25 oC
Corrosion of 304 Stainless Steel in Corrosion of 304 Stainless Steel in Deaerated Sea WaterDeaerated Sea Water
Corrosion Potential
Repassivation PotentialLarge difference means that pits are unlikely to form
Or if a pit forms, then it will passivate
Difference = 0.05 V
WhatWhat’’s on a Polarization Curve?s on a Polarization Curve?
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
1.0E-09 1.0E-06 1.0E-03 1.0E+00 1.0E+03 1.0E+06 1.0E+09
|Current Density| μA/cm2
Pote
ntia
l V(S
HE)
Standard Tafel Behavior
Transition to mass-transfer limited current density
WhatWhat’’s on a Polarization s on a Polarization Curve?Curve?
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
1.0E-09 1.0E-06 1.0E-03 1.0E+00 1.0E+03 1.0E+06 1.0E+09
|Current Density| μA/cm2
Pote
ntia
l V(S
HE)
Net CurrentHydrogen EvolutionOxygen Evolution
Intersection indicates location of the corrosion potential
Current density at corrosion potential also read at intersection
The curve is only valid in aqueous systems and will be bounded by the decomposition of water.
−+ ++→ eHOOH 442 22
−− −+→ eOHHOH 222 22
WhatWhat’’s on a Polarization s on a Polarization Curve?Curve?
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
1.0E-09 1.0E-06 1.0E-03 1.0E+00 1.0E+03 1.0E+06 1.0E+09
|Current Density| μA/cm2
Pote
ntia
l V(S
HE)
Hydrogen EvolutionNet CurrentCorrosionOxygen Evolution
Basic polarization curve with water decomposition and corrosion reaction
WhatWhat’’s on a Polarization s on a Polarization Curve?Curve?
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
1.0E-09 1.0E-06 1.0E-03 1.0E+00 1.0E+03 1.0E+06 1.0E+09
|Current Density| μA/cm2
Pote
ntia
l V(S
HE)
NetHydrogen EvolutionCorrosionH2CO3 ReductionH+ reductionOxygen Evolution
Polarization curve with water decomposition, corrosion reaction and two mass-transfer-limited reactions.
WhatWhat’’s on a Polarization Curve?s on a Polarization Curve?
Active Corrosion
Corrosion Potential and Corrosion current
Passive region
Transpassive regionThis is what is measured experimentally
WhatWhat’’s on a Polarization s on a Polarization Curve?Curve?
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0.001 0.1 10 1000 100000 10000000
|Current Density| μA/cm2
Pote
ntia
l V(S
HE)
Forward SweepReverse Sweep
Polarization curve demonstrating a galvonostatic sweep. The arrows indicate how the potential is changing as one moves along the line.
Transpassive
Passive
Active
There are many processes that There are many processes that make up the polarization curve.make up the polarization curve.
Fe = Fe+2 + 2e-
2H2O=O2+4H++4e-
H2O + e- = ½ H2+OH-
H+ + e- = ½ H2
The Polarization Curve for 304 The Polarization Curve for 304 SS in Deaerated WaterSS in Deaerated Water
Measurable polarization curve
Corrosion of 304 ss
Peak Current density in the pit with the highest corrosion rate
Breakdown of water to H2
Oxidation of water to O2
Open circuit potential and current density
May 20, 1997May 20, 1997 OLI Systems, Inc,OLI Systems, Inc,
Kinetic Model of General Kinetic Model of General Corrosion: PhenomenaCorrosion: Phenomena
Partial electrochemical processes in the active state:Partial electrochemical processes in the active state:Cathodic reactions (e.g., reduction of protons, water molecules,Cathodic reactions (e.g., reduction of protons, water molecules,oxygen, etc.)oxygen, etc.)Anodic reactions (e.g., oxidation of metals)Anodic reactions (e.g., oxidation of metals)
Adsorption of species on the metal surfaceAdsorption of species on the metal surfaceActiveActive--passive transition influenced bypassive transition influenced by
Acid/base properties of passive oxide filmsAcid/base properties of passive oxide filmsTemperatureTemperatureAdditional species that influence the dissolution kinetics of Additional species that influence the dissolution kinetics of oxide layersoxide layers
Synthesis of the partial processes according to the mixed Synthesis of the partial processes according to the mixed potential theorypotential theory
Corrosion of 316 SS in Corrosion of 316 SS in Deaerated WaterDeaerated Water
.00053 mm/yr @25 oC
1886 years to lose 1 mm of metal
Much better corrosion rate than 304 ss
Corrosion of 254 SMO in Corrosion of 254 SMO in Deaerated WaterDeaerated Water
Corrosion rate = 0.00033 mm/yr @ 25 oC
> 3000 years to lose 1 mm of metal
Summary in Deaerated WaterSummary in Deaerated Water
2.72.70.000330.00033254 SMO254 SMO
0.0860.0860.000530.00053316316
0.050.050.00330.0033304304
Potential Potential difference difference (V)(V)
Rate @ 25 Rate @ 25 ooC (mm/yr)C (mm/yr)
StainlessStainless
Adding Air/OxygenAdding Air/Oxygen
The CorrosionAnalyzer The CorrosionAnalyzer allows you to add a gas allows you to add a gas phase based only on phase based only on partial pressurespartial pressuresYou can set the You can set the water/gas ratiowater/gas ratio
0.01 bbl/0.01 bbl/scfscfWGRWGR
0.00030.0003COCO22
0.210.21OO22
0.78970.7897NN22
Partial Partial Pressure Pressure ((atmatm))
SpeciesSpecies
304 SS in Aerated Solution304 SS in Aerated Solution
The corrosion potential is greater than the passivation potential = .37 V at max O2
Pitting will occur
304 SS Polarization in 304 SS Polarization in Aerated WaterAerated Water
0 ppm O2
8 ppm O2
Corrosion potential shifted anodically of the repassivation potential.
The surface will couple galvanicallywith the pits to increase their rate of corrosion.
316 SS Corrosion in Aerated 316 SS Corrosion in Aerated WaterWater
Pitting occurs at higher oxygen concentrations = .21V at max O2
MitigationMitigationChange AlloysChange Alloys
S31254 seems the best at 25 S31254 seems the best at 25 ooCCS31254 increased potential for pitting at higher S31254 increased potential for pitting at higher temperaturestemperatures
Cathodic ProtectionCathodic ProtectionShifting of potential to less corrosive potentials via a Shifting of potential to less corrosive potentials via a sacrificial anode.sacrificial anode.Analyzers do not model CPAnalyzers do not model CPPolarization curves can help determine the change in Polarization curves can help determine the change in potential.potential.
Dealloying of Copper Nickel Dealloying of Copper Nickel AlloysAlloys
ScopeScopeA copperA copper--nickel pipe made of Cupronickel 30 nickel pipe made of Cupronickel 30 has been preferentially has been preferentially dealloyeddealloyed while in while in contact with a 26 weight percent calcium contact with a 26 weight percent calcium chloride brine. It appears that the nickel in the chloride brine. It appears that the nickel in the alloy has been preferentially removed.alloy has been preferentially removed.
Dealloying of Copper Nickel Dealloying of Copper Nickel AlloysAlloys
PurposePurposeThe OLI/CorrosionAnalyzer will be used to The OLI/CorrosionAnalyzer will be used to show the relative stability of nickel and copper show the relative stability of nickel and copper in the cupronickel alloy in an aqueous in the cupronickel alloy in an aqueous solution. It will show that protective films were solution. It will show that protective films were not present as originally thought.not present as originally thought.
Dealloying of Copper Nickel Dealloying of Copper Nickel AlloysAlloys
ObjectivesObjectivesInput information into the software and Input information into the software and perform calculationsperform calculationsUse stability diagrams to display information Use stability diagrams to display information about the alloy and the protective filmsabout the alloy and the protective filmsChange the diagrams to view different Change the diagrams to view different aspects of the stability of the alloyaspects of the stability of the alloy
Application: Dealloying of Application: Dealloying of CopperCopper--Nickel AlloysNickel Alloys
A cupronickel 30 A cupronickel 30 pipe (30 mass % pipe (30 mass % copper) was used.copper) was used.26 wt % CaCl26 wt % CaCl22solution was in solution was in contact with the contact with the pipe.pipe.Nickel was Nickel was preferentially preferentially removed.removed.
Dealloyed cupronickel pipe.
Questions?Questions?
Why did the nickel dealloy from the pipe?Why did the nickel dealloy from the pipe?What could we do to prevent this from What could we do to prevent this from occurring?occurring?Which tools are available to understand Which tools are available to understand this phenomenon?this phenomenon?
Which Tools are Available?Which Tools are Available?
A Pourbaix diagram can help us determine A Pourbaix diagram can help us determine where metals are stable.where metals are stable.
CorrosionAnalyzerCorrosionAnalyzer™™
Creating the First Stability Creating the First Stability DiagramDiagram
We will use the CorrosionAnalyzer We will use the CorrosionAnalyzer ™™ to create a to create a stability diagram for this system.stability diagram for this system.Features of CorrosionAnalyzer Features of CorrosionAnalyzer ™™ diagramsdiagrams
RealReal--solution activity coefficientssolution activity coefficientsElevated temperaturesElevated temperaturesElevated pressuresElevated pressuresInteractions between species and overlay of Interactions between species and overlay of diagrams.diagrams.
The Pourbaix DiagramThe Pourbaix Diagram
There are quite a few things to look at on this There are quite a few things to look at on this diagram.diagram.
Stability field for waterStability field for waterStability fields for nickel metal and copper metalStability fields for nickel metal and copper metalStability fields for nickel and copper oxidesStability fields for nickel and copper oxidesStability fields for aqueous species.Stability fields for aqueous species.
We will now break down the diagram in to more We will now break down the diagram in to more manageable parts.manageable parts.
Stability Diagram FeaturesStability Diagram Features
SubsystemsSubsystemsA base species in its neutral state and all of its A base species in its neutral state and all of its possible oxidation states.possible oxidation states.•• CuCuoo, Cu, Cu+1+1, Cu, Cu+2+2
•• NiNioo, Ni, Ni+2+2
All solids and aqueous species that can be All solids and aqueous species that can be formed from the bulk chemistry for each formed from the bulk chemistry for each oxidation state.oxidation state.
Stability Diagram FeaturesStability Diagram Features
For each subsystemFor each subsystemContact SurfaceContact Surface•• Base metalsBase metals•• AlloysAlloys
FilmsFilms•• SolidsSolids
Solid LinesSolid LinesAqueous LinesAqueous Lines
Stability Diagram FeaturesStability Diagram Features
Natural pHNatural pHPrediction based on the bulk fluid Prediction based on the bulk fluid concentrationsconcentrationsDisplayed as a vertical lineDisplayed as a vertical line
SolidsSolidsAll solids included by defaultAll solids included by defaultThe chemistry can be modified to eliminate The chemistry can be modified to eliminate slow forming solids.slow forming solids.
Stability Diagram FeaturesStability Diagram Features
PassivityPassivityThin, oxidized protective films forming on Thin, oxidized protective films forming on metal or alloy surfaces.metal or alloy surfaces.Transport barrier of corrosive species to metal Transport barrier of corrosive species to metal surface.surface.Blocks reaction sitesBlocks reaction sites
Water StabilityWater Stability
Water can act as an oxidizing agentWater can act as an oxidizing agentWater is reduced to hydrogen, HWater is reduced to hydrogen, H22
Water can act as a reducing agentWater can act as a reducing agentWater is oxidized to oxygen, OWater is oxidized to oxygen, O22
To be stable in aqueous solution, a To be stable in aqueous solution, a species must not react with water through species must not react with water through a redox process.a redox process.
Water StabilityWater Stability
222 HeH →+ −+
[ ] pHH
LogE 059.01059.00 −=⎟⎟⎠
⎞⎜⎜⎝
⎛−= +
OHeOH 22 244 →++ −+
pHE 059.023.1 −=
Water Stability Water Stability –– Natural WatersNatural Waters
Surface water
Ocean waterBog water
Organic rich waterlogged soils
Organic rich lake water
Organic rich saline water
Copper Pourbaix DiagramCopper Pourbaix Diagram
Predominant species
Oxidized Species
Reduced Species
E Independent acid and base chemistry
pH independent redox
pH dependent redox
Copper Pourbaix DiagramCopper Pourbaix Diagram
Stability field for base metal or alloy
Stability field for passivating film
Aqueous species
Equilibrium between species
Equilibrium between species in contact with a solid
Natural pH
Copper Pourbaix DiagramCopper Pourbaix Diagram
Stable copper metal in alloy extending into water stability field.
Copper pipes are used for potable water for this reason.
The solution pH is in a region where the copper metal will be stable.
Nickel Pourbaix DiagramNickel Pourbaix Diagram
No Nickel metal extends into the water stability field The solution pH is in a region
where nickel is expected to corrode
Ni Overlaid on CuNi Overlaid on Cu
Since the nickel is part of a copper-nickel alloy, it is possible that copper could provide a protective film
CuCl(s) may form to protect the alloy at the solution pH.
We need to know the Oxidation/Reduction potential
CorrosionAnalyzer CalculationCorrosionAnalyzer Calculation
The oxidation reduction potential is 0.463 V
Ni Overlaid on CuNi Overlaid on Cu
The potential of 0.463 V lies above the passivating film. Dealloying can occur.
ConclusionsConclusions
Why did Why did dealloyingdealloying occur?occur?No protective film at the operating pH and No protective film at the operating pH and oxidation/reduction potential of the process fluid.oxidation/reduction potential of the process fluid.Copper lies within the region of water stabilityCopper lies within the region of water stabilityNickel does not lie within the region of water stabilityNickel does not lie within the region of water stabilityThe presence of CuThe presence of Cu++ ions in equilibrium with copper ions in equilibrium with copper metal promotes metal promotes replatingreplating of copper metal driven by of copper metal driven by the oxidation of nickel.the oxidation of nickel.
ChemistryChemistry
Standard OLI ChemistryStandard OLI Chemistry7400 components7400 components9100 individual species9100 individual species82 Elements of the Periodic Table fully 82 Elements of the Periodic Table fully coveredcovered•• 8 additional elements partially covered.8 additional elements partially covered.
Stability diagrams have access all of this Stability diagrams have access all of this chemistrychemistry
ChemistryChemistry
AlloysAlloys6 predefined classes supported6 predefined classes supported•• CuCu--NiNi•• Carbon Steels Carbon Steels –– Fe, Fe, MnMn, and C, and C•• FerriticFerritic Stainless steels Stainless steels –– Fe, Cr, Ni, Mo and CFe, Cr, Ni, Mo and C•• Austenitic stainless steels Austenitic stainless steels -- Fe, Cr, Ni, Mo and CFe, Cr, Ni, Mo and C•• Duplex stainless steels FCC phase Duplex stainless steels FCC phase -- Fe, Cr, Ni, Fe, Cr, Ni,
Mo, C and NMo, C and NUser defined alloysUser defined alloys
Limits to the Standard OLI Limits to the Standard OLI ChemistryChemistry
Aqueous Phase
XH2O > 0.65
-50oC < T < 300oC
0 Atm < P < 1500 Atm
0 < I < 30
Non-aqueous Liquid
Currently no Activity Coefficient Model (i.e., no NRTL, Unifaq/Uniqac)
Fugacity Coefficients are determined from the Enhanced SRK
Limitations of Pourbaix Limitations of Pourbaix DiagramsDiagrams
No information on corrosion kinetics is provided.No information on corrosion kinetics is provided.Diagram is produced from only thermodynamics.Diagram is produced from only thermodynamics.
Diagram is valid only for the calculated Diagram is valid only for the calculated temperature and pressuretemperature and pressureOxide stability fields are calculated Oxide stability fields are calculated thermodynamically and may not provide an thermodynamically and may not provide an actual protective film.actual protective film.Dealloying cannot be predicted from the diagram Dealloying cannot be predicted from the diagram alone.alone.