understanding the corrosion environment teach-in the corrosion
TRANSCRIPT
Understanding the corrosion Understanding the corrosion environmentenvironment
Teach-inTeach-inThe CorrosionThe Corrosion
Any method be made more effective…Any method be made more effective…
CouponsCoupons
Online MonitorsOnline Monitors
Inhibition 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
5.5% NaCl
5.5% NaCl, 5 atm
5.5% NaCl, 85 °C
5.5% NaCl, 10 °C, 15 atm
It helps to know the effect It helps to know the effect of variations in the fieldof variations in the field
To interpret To interpret coupon and coupon and monitor data…monitor data…
Wait for a failure…?Wait for a failure…?
Rely on past experience?Rely on past experience?
To locate where To locate where to place sensors & to place sensors & coupons…coupons…
Tell you what has already Tell you what has already happened, happened, notnot what will what will
happenhappen
CouponsCoupons
Online MonitorsOnline Monitors
OLI tools can helpOLI tools can help
OLI OLI getsgetsthethechemistrychemistryrightright
?Phase splitsDew pointpH
Protective Scale
Passive 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 Screen alloys and inhibitorsinhibitors• 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 toolMechanistically-based software tool Mechanistically-based software toolMechanistically-based software tool
Tool for understanding the corrosion environment
SpeciationSpeciationKinetics of uniform corrosionKinetics of uniform corrosion
Partial anodic and Partial anodic and cathodic cathodic processesprocessesTransport propertiesTransport propertiesRepassivationRepassivation
SpeciationSpeciationKinetics of uniform corrosionKinetics of uniform corrosion
Partial anodic and Partial anodic and cathodic cathodic processesprocessesTransport propertiesTransport propertiesRepassivationRepassivation
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
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
Thermophysical properties predictionThermophysical properties prediction
Phenomenological and unique aqueous Phenomenological and unique aqueous process models including kinetics and process models including kinetics and transporttransport
““Out-of-the-box” solution and technical Out-of-the-box” solution and technical supportsupport
The Corrosion AnalyzerThe Corrosion AnalyzerBased on the OLI Engine
What It Does…What It Does…What It Does…What It Does…
Predict metal dissolution regime, passive Predict metal dissolution regime, passive films, and surface depositsfilms, and surface deposits
Predict metal dissolution regime, passive Predict metal dissolution regime, passive films, and surface depositsfilms, and surface deposits
Predict uniform Predict uniform corrosion rates and the corrosion rates and the potential for pitting potential for pitting corrosioncorrosion
Generate real solution Generate real solution stability (Pourbaix) stability (Pourbaix) DiagramsDiagrams
Produce theoretical Produce theoretical polarization curvespolarization curves
Predict uniform Predict uniform corrosion rates and the corrosion rates and the potential for pitting potential for pitting corrosioncorrosion
Generate real solution Generate real solution stability (Pourbaix) stability (Pourbaix) DiagramsDiagrams
Produce 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 …So you can gain insight on …
Corrosion mechanisms Corrosion mechanisms Rate-limiting partial processes for your Rate-limiting partial processes for your
operating conditionsoperating conditions Effects of process and materials changesEffects of process and materials changes
Corrosion mechanisms Corrosion mechanisms Rate-limiting partial processes for your Rate-limiting partial processes for your
operating conditionsoperating conditions Effects of process and materials changesEffects of process and materials changes
ThereforeTherefore Focusing lab time Focusing lab time Reducing risky plant/field Reducing risky plant/field
testingtesting Managing design, Managing design,
operation, and operation, and maintenancemaintenance
ThereforeTherefore Focusing lab time Focusing lab time Reducing risky plant/field Reducing risky plant/field
testingtesting Managing design, Managing design,
operation, and operation, and maintenancemaintenance
The Corrosion AnalyzerThe Corrosion Analyzer
Today’s seminar
“Hands-on” and “How-To”Hands-on” and “How-To”
Using example problemsUsing example problems
Examining plots and Examining plots and
diagramsdiagrams
Understanding the basis ofUnderstanding the basis of
the predictionsthe predictions
Today’s seminar
“Hands-on” and “How-To”Hands-on” and “How-To”
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” calculationsPerform “Single point” calculations Construct / interpret real solution Pourbaix Construct / interpret real solution Pourbaix
DiagramsDiagrams Calculate 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
Perform “Single point” calculationsPerform “Single point” calculations Construct / interpret real solution Pourbaix Construct / interpret real solution Pourbaix
DiagramsDiagrams Calculate 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
Welcome to the
CORROSION TEACH-IN
Simulating Real World Corrosion Problems
Gas Condensate CorrosionGas Condensate Corrosion
ScopeScope Gas condensates from alkanolamine gas Gas condensates from alkanolamine gas
sweetening plants can be highly corrosive.sweetening plants can be highly corrosive. PurposePurpose
Diethanolamine 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
ObjectivesObjectives Determine the dew point of the acid gasDetermine the dew point of the acid gas Remove the condensed phase and perform Remove the condensed phase and perform
corrosion rate calculationscorrosion rate calculations Mitigate the corrosionMitigate the corrosion
Gas SweeteningGas SweeteningSour Gas Absorber
Absorber liquor regenerator
Acid Gas
Acid Gas ConcentrationsAcid Gas Concentrations
SpeciesSpecies Concentration (mole %)Concentration (mole %)
HH22OO 5.425.42
COCO22 77.477.4
NN22 0.020.02
HH22SS 16.616.6
MethaneMethane 0.500.50
EthaneEthane 0.030.03
PropanePropane 0.030.03
TemperatureTemperature 38 38 ooCC
PressurePressure 1.2 Atm.1.2 Atm.
AmountAmount 100 moles100 moles
Application TimeApplication Time
Dew PointDew Point
•Dew Point = 37.6 oC
•pH = 3.93
•ORP = 0.576 V
Corrosion Rates: Flow Corrosion Rates: Flow ConditionsConditions
Flow conditions have a direct effect on Flow conditions have a direct effect on mass-transfermass-transfer StaticStatic Pipe flowPipe flow Rotating diskRotating disk Rotating cylinderRotating cylinder Complete agitationComplete agitation
Application TimeApplication Time
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 A/cm2
MitigationMitigation
Adjusting solution chemistryAdjusting solution chemistry Temperature profilingTemperature profiling Alloy screeningAlloy screening Cathodic protectionCathodic protection
Adjusting the Solution Adjusting the Solution ChemistryChemistry
Changing operating pHChanging operating pH Add acid or baseAdd acid or base
Application TimeApplication Time
Adjusting solution pH = 8.0Adjusting solution pH = 8.0
Screening AlloysScreening Alloys
Select an alloy that has a preferential Select an alloy that has a preferential corrosion ratecorrosion rate 13% chromium13% chromium 304 Stainless304 Stainless
Application TimeApplication Time
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 A/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 A/cm2
304 Stainless Steel Stability @ Dew Point304 Stainless Steel Stability @ Dew Point
Passivation is possible due to Cr2O3
Why Iron RustsWhy Iron Rusts
Explaining common observations Explaining common observations using Stability Diagramsusing Stability Diagrams
BasicsBasics Iron 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
Start example
Explaining the EH-pH diagram using Fe, showing solid and dissolved species over range of pH’s and oxidation
potentials
H2O is oxidized to O
2 and H+
H2O is reduced to H
2 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 aeratedFe
2O3 reduces and dissolves in water
Fe(II) oxidizes and precipitates as Fe2O
3
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 O
2 and H+
H2O is stable and aerated
Water Oxidation Line
eHOOH 2221
22
H2O is reduced to H
2 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)
OHHFeOHFe
eFeFe
OHHeOH
o
o
22
2
222
22
2
2
22
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
Why is Stainless Steel Why is Stainless Steel stainless?stainless?
Cr will oxidizes, but the reaction goes through a tough Cr2O3 protective layer.
Ni3Fe2O4 is stable in the corrosion region, and will also protect the surface.
Welcome to the
CORROSION TEACH-IN
Simulating Real World Corrosion Problems
Corrosion in SeawaterCorrosion in Seawater
ScopeScope Metals 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
PurposePurpose Chlorine 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
ObjectivesObjectives Reconcile a sea water sample for Reconcile a sea water sample for
electroneutralityelectroneutrality Reconcile a gas analysisReconcile a gas analysis Calculate 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: Mass-TransferCorrosion: Mass-Transfer
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 mass-transfer-limited Reduce mass-transfer-limited
currents.currents.
Mass-transfer from solution is Mass-transfer from solution is calculated from a concentration- calculated 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
• H H 22O, OO, O22, CO, CO22, H , H 22S, NS, N22 and all inert gases, Cl and 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--, Cl, Cl--, Br, Br--, I, I--, HCO, HCO33--, CO, CO33
-2-2, HS, HS--, S, S2-2-, SO, SO442-2-, HSO, HSO44
--, SO, SO332-2-, ,
NONO22--, NO, NO33
--, MoO, MoO442-2-, CN, CN--, ClO, ClO44
--, ClO, ClO33--, ClO, ClO--, 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 Si(IV) anions.B(III) anions and Si(IV) 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, Cd(II) cations, Fe(III) cations, Al(III) cations, Cd(II) cations, Sn(II) cations, Zn(II) cations, Cu(II) cations, Sn(II) cations, Zn(II) cations, Cu(II) cations, Pb(II) cations and NHcations, Pb(II) 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 electroneutralityelectroneutrality
NaOH/HCl Used NaOH/HCl Used to adjust pHto adjust pH
SpeciesSpecies ConcentratiConcentration (mg/L)on (mg/L)
ClCl-- 1900019000
NaNa++ 1070010700
MgMg+2+2 13001300
CaCa+2+2 400400
SOSO44-2-2 27502750
HCOHCO33-- 150150
pHpH 8.08.0
TemperatuTemperaturere
25 25 ooCC
PressurePressure 1 atm.1 atm.
Application TimeApplication Time
Screening ConsiderationsScreening Considerations
Some alloys do not perform well in Some alloys do not perform well in seawaterseawater
We will evaluate 3 stainless steelsWe will evaluate 3 stainless steels Uniform corrosion ratesUniform corrosion rates Pitting 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
Application TimeApplication Time
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 316 SS in Corrosion of 316 SS in Deaerated WaterDeaerated Water
Difference = 0.086 V
Application TimeApplication Time
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
Corrosion of 254 SMO in Corrosion of 254 SMO in Deaerated WaterDeaerated Water
Difference = 2.7 V
Summary in Deaerated WaterSummary in Deaerated Water
StainlessStainless Rate @ 25 Rate @ 25 ooC (mm/yr)C (mm/yr)
Potential Potential difference difference (V)(V)
304304 0.00330.0033 0.050.05
316316 0.000530.00053 0.0860.086
254 SMO254 SMO 0.000330.00033 2.72.7
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 pressures
You can set the You can set the water/gas ratiowater/gas ratio
SpeciesSpecies Partial Partial Pressure Pressure (atm)(atm)
NN22 0.78970.7897
OO22 0.210.21
COCO22 0.00030.0003
WGRWGR 0.01 bbl/scf0.01 bbl/scf
Application TimeApplication Time
304 SS in Aerated Solutions304 SS in Aerated Solutions
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
Application TimeApplication Time
316 SS Corrosion in Aerated 316 SS Corrosion in Aerated WaterWater
Pitting occurs at higher oxygen concentrations = .21V at max O2
Application TimeApplication Time
S31254 Corrosion in Deaerated S31254 Corrosion in Deaerated WaterWater
Pitting should not occur
Stability Diagram for 316L SSStability Diagram for 316L SS
Stability Diagram for 316 LStability Diagram for 316 LNickel OnlyNickel Only
MitigationMitigation
Change AlloysChange Alloys S31254 seems the best at 25 S31254 seems the best at 25 ooCC S31254 increased potential for pitting at higher S31254 increased potential for pitting at higher
temperaturestemperatures Cathodic ProtectionCathodic Protection
Shifting 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 CP Polarization curves can help determine the change in Polarization curves can help determine the change in
potential.potential.
Welcome to the
CORROSION TEACH-IN
Simulating Real World Corrosion Problems
Dealloying of Copper Nickel Dealloying of Copper Nickel AlloysAlloys
ScopeScope A copper-nickel pipe made of Cupronickel 30 A copper-nickel pipe made of Cupronickel 30
has been preferentially dealloyed while in has been preferentially dealloyed 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
PurposePurpose The 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
ObjectivesObjectives Input information into the software and Input information into the software and
perform calculationsperform calculations Use stability diagrams to display information Use stability diagrams to display information
about the alloy and the protective filmsabout the alloy and the protective films Change 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 Copper-Nickel AlloysCopper-Nickel Alloys
A cupronickel 30 A cupronickel 30 pipe (30 mass % pipe (30 mass % copper) was used.copper) was used.
26 wt % CaCl26 wt % CaCl22 solution 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 diagrams diagrams Real-solution activity coefficientsReal-solution activity coefficients Elevated temperaturesElevated temperatures Elevated pressuresElevated pressures Interactions between species and overlay of Interactions between species and overlay of
diagrams.diagrams.
The Pourbaix DiagramThe Pourbaix Diagram
Application TimeApplication Time
Time to start working with the OLI Corrosion Analyzer
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 water Stability fields for nickel metal and copper metalStability fields for nickel metal and copper metal Stability fields for nickel and copper oxidesStability fields for nickel and copper oxides Stability 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
SubsystemsSubsystems A base species in its neutral state and all of A base species in its neutral state and all of
its possible oxidation states.its 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 subsystem Contact SurfaceContact Surface
• Base metalsBase metals• AlloysAlloys
FilmsFilms• SolidsSolids
Solid LinesSolid Lines Aqueous LinesAqueous Lines
Stability Diagram FeaturesStability Diagram Features
Natural pHNatural pH Prediction based on the bulk fluid Prediction based on the bulk fluid
concentrationsconcentrations Displayed as a vertical lineDisplayed as a vertical line
SolidsSolids All solids included by defaultAll solids included by default The chemistry can be modified to eliminate The chemistry can be modified to eliminate
slow forming solids.slow forming solids.
Stability Diagram FeaturesStability Diagram Features
PassivityPassivity Thin, 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 agent Water is reduced to hydrogen, HWater is reduced to hydrogen, H22
Water can act as a reducing agentWater can act as a reducing agent Water 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.
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
Application TimeApplication Time
CorrosionAnalyzer CalculationCorrosionAnalyzer Calculation
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 dealloying occur?Why did dealloying 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 stability Nickel does not lie within the region of water stabilityNickel does not lie within the region of water stability The presence of CuThe presence of Cu++ ions in equilibrium with copper ions in equilibrium with copper
metal promotes replating of copper metal driven by metal promotes replating of copper metal driven by the oxidation of nickel.the oxidation of nickel.
ChemistryChemistry
Standard OLI ChemistryStandard OLI Chemistry 7400 components7400 components 9100 individual species9100 individual species 82 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
AlloysAlloys 6 predefined classes supported6 predefined classes supported
• Cu-NiCu-Ni• Carbon Steels – Fe, Mn, and CCarbon Steels – Fe, Mn, and C• Ferritic Stainless steels – Fe, Cr, Ni, Mo and CFerritic Stainless steels – Fe, Cr, Ni, Mo and C• Austenitic stainless steels - Fe, Cr, Ni, Mo and CAustenitic stainless steels - Fe, Cr, Ni, Mo and C• Duplex stainless steels FCC phase - Fe, Cr, Ni, Duplex stainless steels FCC phase - Fe, Cr, Ni,
Mo, C and NMo, C and N User 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 pressure
Oxide 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.