understanding the corrosion environment teach-in the corrosion

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.