Corrosion Teach in PPT

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

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 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

OLI tools can helpOLI tools can helpOLI OLI getsgetsthethechemistrychemistryrightright

Phase splitsDew pointpH

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


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


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

Welcome to the

CORROSION TEACH-IN

Simulating Real World Corrosion Problems

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

Gas SweeteningGas SweeteningSour Gas Absorber

Absorber liquor regenerator

Acid Gas

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

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 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


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% 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





304 Stainless Steel Corrosion @ Dew Point304 Stainless Steel Corrosion @ Dew Point





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

+→+

+→

+→+−+

−−

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 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

Start example on Page 36-39

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

Start example on Page 40-41

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

Why is Stainless Steel Why is Stainless Steel stainless?stainless?

Cr will oxidizes, but the reaction goes through a tough Cr2O3protective layer.

Ni3Fe2O4 is stable in the corrosion region, and will also protect the surface.

Welcome to the

CORROSION TEACH-IN


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.


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.


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


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


300 years to lose 1 mm of metal

.0033 mm/yr @ 25 oC


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


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


-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


Pote

ntia

l V(S

HE)

Hydrogen EvolutionNet CurrentCorrosionOxygen Evolution

Basic polarization curve with water decomposition and corrosion reaction


-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


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


-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0.001 0.1 10 1000 100000 10000000


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 316 SS in Corrosion of 316 SS in Deaerated WaterDeaerated Water

Difference = 0.086 V


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

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 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

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


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

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.

Welcome to the

CORROSION TEACH-IN


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.


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.


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


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 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.


For each subsystemFor each subsystemContact SurfaceContact Surface•• Base metalsBase metals•• AlloysAlloys

FilmsFilms•• SolidsSolids

Solid LinesSolid LinesAqueous LinesAqueous Lines


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.


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


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


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

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.

Documents

Corrosion Teach in PPT