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Understanding the corrosion environment Teach-in The Corrosion.

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1 Understanding the corrosion environment Teach-in The Corrosion

2 Any method be made more effective… Coupons Online Monitors Inhibition programs Different methods for corrosion control

3 …When you understand the effect of the corrosion environment Corrosion rates vary with process conditions

4 5.5% NaCl

5 5.5% NaCl, 5 atm

6 5.5% NaCl, 85 °C

7 5.5% NaCl, 10 °C, 15 atm

8 It helps to know the effect of variations in the field To interpret coupon and monitor data …

9 Wait for a failure…? Rely on past experience? To locate where to place sensors & coupons …

10 Tell you what has already happened, not what will happen Coupons Online Monitors

11 OLI tools can help OLI gets the chemistry right

12 ? Phase splits Dew point pH

13 Protective ScalePassive FilmActive Corrosion (dissolution) pH Understand whats happening in your system

14 Determine the rate limiting redox processes Rate-limiting cathodic process Activation controlled Passive region

15 Determine pitting potential and max growth rate Pitting No Pitting

16 Test Corrective Actions Test Corrective Actions Determine optimum pHDetermine optimum pH Screen alloys and inhibitorsScreen alloys and inhibitors Assess process changesAssess process changes Focus Lab work Focus Lab work Eliminate potential problems before they occur Eliminate potential problems before they occur Pro-active Analysis

17 The Corrosion Analyzer Mechanistically-based software tool Mechanistically-based software tool Tool for understanding the corrosion environment Speciation Speciation Kinetics of uniform corrosion Partial anodic and cathodic processes Kinetics of uniform corrosion Partial anodic and cathodic processes Transport properties Transport properties Repassivation Repassivation Speciation Speciation Kinetics of uniform corrosion Partial anodic and cathodic processes Kinetics of uniform corrosion Partial anodic and cathodic processes Transport properties Transport properties Repassivation Repassivation

18 Complete speciation model for complex mixtures Complete speciation model for complex mixtures Phase and chemical reaction equilibria Phase and chemical reaction equilibria Accurate pH prediction Accurate pH prediction Redox chemistry Redox chemistry Comprehensive coverage of industrial chemical and petroleum systems Comprehensive coverage of industrial chemical and petroleum systems Complete speciation model for complex mixtures Complete speciation model for complex mixtures Phase and chemical reaction equilibria Phase and chemical reaction equilibria Accurate pH prediction Accurate pH prediction Redox chemistry Redox chemistry Comprehensive coverage of industrial chemical and petroleum systems Comprehensive coverage of industrial chemical and petroleum systems The Corrosion Analyzer Based on the OLI Engine

19 Thermophysical properties prediction Thermophysical properties prediction Phenomenological and unique aqueous process models including kinetics and transport Phenomenological and unique aqueous process models including kinetics and transport Out-of-the-box solution and technical support Out-of-the-box solution and technical support The Corrosion Analyzer Based on the OLI Engine

20 What It Does… Predict metal dissolution regime, passive films, and surface deposits Predict metal dissolution regime, passive films, and surface deposits Predict uniform corrosion rates and the potential for pitting corrosion Predict uniform corrosion rates and the potential for pitting corrosion Generate real solution stability (Pourbaix) Diagrams Generate real solution stability (Pourbaix) Diagrams Produce theoretical polarization curves Produce theoretical polarization curves Predict uniform corrosion rates and the potential for pitting corrosion Predict uniform corrosion rates and the potential for pitting corrosion Generate real solution stability (Pourbaix) Diagrams Generate real solution stability (Pourbaix) Diagrams Produce theoretical polarization curves Produce theoretical polarization curves The Corrosion Analyzer

21 So you can gain insight on … Corrosion mechanisms Corrosion mechanisms Rate-limiting partial processes for your operating conditions Rate-limiting partial processes for your operating conditions Effects of process and materials changes Effects of process and materials changes Corrosion mechanisms Corrosion mechanisms Rate-limiting partial processes for your operating conditions Rate-limiting partial processes for your operating conditions Effects of process and materials changes Effects of process and materials changes Therefore Focusing lab time Focusing lab time Reducing risky plant/field testing Reducing risky plant/field testing Managing design, operation, and maintenance Managing design, operation, and maintenanceTherefore Focusing lab time Focusing lab time Reducing risky plant/field testing Reducing risky plant/field testing Managing design, operation, and maintenance Managing design, operation, and maintenance The Corrosion Analyzer

22 Todays seminar Hands-on and How-ToHands-on and How-To Using example problems Using example problems Examining plots and diagrams Examining plots and diagrams Understanding the basis of the predictions Understanding the basis of the predictions Todays seminar Hands-on and How-ToHands-on and How-To Using example problems Using example problems Examining plots and diagrams Examining plots and diagrams Understanding the basis of the predictions Understanding the basis of the predictions

23 Perform Single point calculations Perform Single point calculations Construct / interpret real solution Pourbaix Diagrams Construct / interpret real solution Pourbaix Diagrams Calculate corrosion rates Calculate corrosion rates Evaluate the effects of pH, T, comp / flow Evaluate the effects of pH, T, comp / flow Evaluate polarization curves Gain insight to corrosion mechanisms See 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 Single point calculations Perform Single point calculations Construct / interpret real solution Pourbaix Diagrams Construct / interpret real solution Pourbaix Diagrams Calculate corrosion rates Calculate corrosion rates Evaluate the effects of pH, T, comp / flow Evaluate the effects of pH, T, comp / flow Evaluate polarization curves Gain insight to corrosion mechanisms See 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 Todays Seminar

24 Welcome to the CORROSION TEACH-IN Simulating Real World Corrosion Problems

25 Gas Condensate Corrosion Scope Scope Gas condensates from alkanolamine gas sweetening plants can be highly corrosive. Gas condensates from alkanolamine gas sweetening plants can be highly corrosive. Purpose Purpose Diethanolamine is used to neutralize (sweeten) a natural gas stream. This removes carbon dioxide and hydrogen sulfide. The off gas from the regeneration is highly acidic and corrosive Diethanolamine is used to neutralize (sweeten) a natural gas stream. This removes carbon dioxide and hydrogen sulfide. The off gas from the regeneration is highly acidic and corrosive

26 Gas Condensate Corrosion Objectives Objectives Determine the dew point of the acid gas Determine the dew point of the acid gas Remove the condensed phase and perform corrosion rate calculations Remove the condensed phase and perform corrosion rate calculations Mitigate the corrosion Mitigate the corrosion

27 Gas Sweetening Sour Gas Absorber Absorber liquor regenerator Acid Gas

28 Acid Gas Concentrations Species Concentration (mole %) H2OH2OH2OH2O5.42 CO N2N2N2N20.02 H2SH2SH2SH2S16.6 Methane0.50 Ethane0.03 Propane0.03 Temperature 38 o C Pressure 1.2 Atm. Amount 100 moles

29 Application Time

30 Dew Point Dew Point = 37.6 o C pH = 3.93 ORP = V

31 Corrosion Rates: Flow Conditions Flow conditions have a direct effect on mass-transfer Flow conditions have a direct effect on mass-transfer Static Static Pipe flow Pipe flow Rotating disk Rotating disk Rotating cylinder Rotating cylinder Complete agitation Complete agitation

32 Application Time

33 Carbon Steel Dew Point H 2 CO 3(aq) = ½ H + + HCO e HS - = ½ H 2 + S 2- - e H + = ½ H 2 - e H 2 S (aq) = ½ H 2 + HS - - e Corrosion Rate = 0.7 mm/yr Corrosion Potential = V Repassivation Potential = > 2 V Current Density = 60.5 A/cm 2

34 Mitigation Adjusting solution chemistry Adjusting solution chemistry Temperature profiling Temperature profiling Alloy screening Alloy screening Cathodic protection Cathodic protection

35 Adjusting the Solution Chemistry Changing operating pH Changing operating pH Add acid or base Add acid or base

36 Application Time

37 Adjusting solution pH = 8.0

38 Screening Alloys Select an alloy that has a preferential corrosion rate Select an alloy that has a preferential corrosion rate 13% chromium 13% chromium 304 Stainless 304 Stainless

39 Application Time

40 13 % Cr Steel Dew Point H 2 CO 3(aq) = ½ H + + HCO e HS - = ½ H 2 + S 2- - e Corrosion Rate = 0.06 mm/yr Corrosion Potential = V Repassivation Potential = > 2 V Current Density = 5.7 A/cm 2

41 304 Stainless Steel Dew Point Corrosion Rate = mm/yr Corrosion Potential = V Repassivation Potential = > 2 V Current Density = 0.3 A/cm 2

42 304 Stainless Steel Dew Point Passivation is possible due to Cr 2 O 3

43 Why Iron Rusts Explaining common observations using Stability Diagrams

44 Basics Iron is inherently unstable in water & oxidizes via the following reactions to form rust Iron is inherently unstable in water & oxidizes via the following 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 potential oxidation potential These four can be plotted on a single chart called a stability diagram These four can be plotted on a single chart called a stability diagram

45 Start example

46 Explaining the EH-pH diagram using Fe, showing solid and dissolved species over range of pHs and oxidation potentials H 2 O is oxidized to O 2 and H + H 2 O is reduced to H 2 and OH - Elemental iron, Fe(0) o, is stable and will not corrode in this region H 2 O is stable and deaerated H 2 O is stable and aerated Fe 2 O 3 reduces and dissolves in water Fe(II) oxidizes and precipitates as Fe 2 O 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 pHs White area is region of iron corrosion Water Oxidation Line Water Reduction Line Fe 3 O 4 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 Fe 0 to Fe +2 which dissolves in water (white region of the plot). As the oxidation potential increases (high dissolved O 2 ) Fe +2 precipitates as FeOOH, or rust (green region). The lower the pH, the thicker the white region and the greater driving force for corrosion At higher pH (10-11), Fe 0 forms Fe 3 O 4, a stable solid that precipitates on the iron surface, protecting it from further attack.

47 H 2 O is oxidized to O 2 and H + H 2 O is stable and aerated Water Oxidation Line H 2 O is reduced to H 2 and OH - H 2 O is stable and deaerated Water Reduction Line Q: We all know O 2 is bad…But how much is bad? Pure water is here… No air, no acid, no base 0.1 ppT H ppT O ppb H 2 3 ppb O 2 10 ppm O 2 0.1ppm H ppm O 2 80 ppm H 2

48 Elemental Iron (Fe o ) Iron and water react because they are not stable together Region of instability The reaction generates H 2, which puts the EH near the bottom line The reaction generates 2OH -, which increases the pH

49 Start example on Page 36-39

50 Initial Conditions DI water, no Fe o 7pH, 0.4V Final Conditions 1 ppm Fe o added 9.38pH, 0.5V 0.9 ppb Fe o 7.07pH, -0.27V 0.1 ppm Fe o 8.48pH, -0.42V The reaction ends within the Fe 3 O 4 region. Fe 3 O 4 is a solid that passivates the iron surface protecting it from active corrosion

51 1.4 g Fe 3 O 4 ppts from 1 Fe o Fe 3 O 4 precipitates when 0.3 mg/l Fe o has reacted The ppt point lines up with the stability curve Overlaying the Fe3O4 mass on the diagram – once the pH reached 9, Fe3O4 began to precipitate

52 Start example on Page 40-41

53 The EH and pH does not change as Fe o reacts with aerated water If a constant source of O2 is present, then the EH and pH do not change, and we are stuck in the rust region

54 Why is Stainless Steel stainless?

55 Cr will oxidizes, but the reaction goes through a tough Cr 2 O 3 protective layer.

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

57 Welcome to the CORROSION TEACH-IN Simulating Real World Corrosion Problems

58 Corrosion in Seawater Scope Scope Metals used for handling sea water face both general and localized corrosion. Metals used for handling sea water face both general and localized corrosion. Various grades of stainless steels have been used to mitigate the problems. Various grades of stainless steels have been used to mitigate the problems. Stainless steels owe their corrosion resistance to a thin adherent film of oxides on their surface. Stainless steels owe their corrosion resistance to a thin adherent film of oxides on their surface. Disruption of the films can lead to localized corrosion and premature failure. Disruption of the films can lead to localized corrosion and premature failure.

59 Corrosion in Seawater Purpose Purpose Chlorine and oxygen in sea water can attack the films used to passivate the steels. Chlorine and oxygen in sea water can attack the films used to passivate the steels. The CorrosionAnalyzer will be used to model the effects of chloride and oxygen on the rates of uniform corrosion and the possibility of pitting on the surface of the metals. The CorrosionAnalyzer will be used to model the effects of chloride and oxygen on the rates of uniform corrosion and the possibility of pitting on the surface of the metals.

60 Corrosion in Seawater Objectives Objectives Reconcile a sea water sample for electroneutrality Reconcile a sea water sample for electroneutrality Reconcile a gas analysis Reconcile a gas analysis Calculate uniform rates of corrosion for Calculate uniform rates of corrosion for 304 stainless steel304 stainless steel 316 stainless steel316 stainless steel S31254 stainless steelS31254 stainless steel

61 Corrosion in Seawater Objectives (continued) Objectives (continued) Determine the probability of pitting using the localized corrosion feature. Determine the probability of pitting using the localized corrosion feature.

62 Kinetic Model of General Corrosion: Mass-Transfer All reactions take place on the metal surface. All reactions take place on the metal surface. Films are a diffusion barrier to corrosive species Films are a diffusion barrier to corrosive species Reduce mass-transfer-limited currents. Reduce mass-transfer-limited currents. Mass-transfer from solution is calculated from a concentration- dependent diffusion coefficient. Mass-transfer from solution is calculated from a concentration- dependent diffusion coefficient. film Metal Surface Solution

63 Chemistry The rates of corrosion use a subset of the OLI Chemistry The rates of corrosion use a subset of the OLI Chemistry Neutral Species Neutral Species H­ 2 O, O 2, CO 2, H­ 2 S, N 2 and all inert gases, Cl 2, SO 2, S o and NH 3, organic molecules that do not undergo electrochemical reactionsH­ 2 O, O 2, CO 2, H­ 2 S, N 2 and all inert gases, Cl 2, SO 2, S o and NH 3, organic molecules that do not undergo electrochemical reactions Anions Anions OH -, Cl -, Br -, I -, HCO 3 -, CO 3 -2, HS -, S 2-, SO 4 2-, HSO 4 -, SO 3 2-, NO 2 -, NO 3 -, MoO 4 2-, CN -, ClO 4 -, ClO 3 -, ClO -, acetate, formate, Cr(VI) anions, As(III) anions, P(V) anions, W(VI) anions, B(III) anions and Si(IV) anions.OH -, Cl -, Br -, I -, HCO 3 -, CO 3 -2, HS -, S 2-, SO 4 2-, HSO 4 -, SO 3 2-, NO 2 -, NO 3 -, MoO 4 2-, CN -, ClO 4 -, ClO 3 -, ClO -, acetate, formate, Cr(VI) anions, As(III) anions, P(V) anions, W(VI) anions, B(III) anions and Si(IV) anions.

64 Chemistry Cations Cations H +, alkali metals, alkaline earth metals, Fe(II) cations, Fe(III) cations, Al(III) cations, Cd(II) cations, Sn(II) cations, Zn(II) cations, Cu(II) cations, Pb(II) cations and NH 4 +.H +, alkali metals, alkaline earth metals, Fe(II) cations, Fe(III) cations, Al(III) cations, Cd(II) cations, Sn(II) cations, Zn(II) cations, Cu(II) cations, Pb(II) cations and NH 4 +.

65 Corrosion of 304 Stainless Steel in Deaerated Sea Water LabAnalyzer used to reconcile electroneutrality LabAnalyzer used to reconcile electroneutrality NaOH/HCl Used to adjust pH NaOH/HCl Used to adjust pH Species Concentrati on (mg/L) Cl Na Mg Ca SO HCO pH8.0 Temperatur e 25 o C Pressure 1 atm.

66 Application Time

67 Screening Considerations Some alloys do not perform well in seawater Some alloys do not perform well in seawater We will evaluate 3 stainless steels We will evaluate 3 stainless steels Uniform corrosion rates Uniform corrosion rates Pitting possibility Pitting possibility Considering both deaerated and aerated conditions Considering both deaerated and aerated conditions

68 Corrosion of 304 Stainless Steel in Deaerated Sea Water 300 years to lose 1 mm of metal o C

69 Corrosion of 304 Stainless Steel in Deaerated Sea Water Corrosion Potential Repassivation Potential Large difference means that pits are unlikely to form Or if a pit forms, then it will passivate Difference = 0.05 V

70 Whats on a Polarization Curve? Standard Tafel Behavior Transition to mass-transfer limited current density

71 Whats on a Polarization Curve? 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.

72 Whats on a Polarization Curve? Basic polarization curve with water decomposition and corrosion reaction

73 Whats on a Polarization Curve? Polarization curve with water decomposition, corrosion reaction and two mass-transfer-limited reactions.

74 Whats on a Polarization Curve? Active Corrosion Corrosion Potential and Corrosion current Passive region Transpassive region This is what is measured experimentally

75 Whats on a Polarization Curve? Polarization curve demonstrating a galvonostatic sweep. The arrows indicate how the potential is changing as one moves along the line. Transpassive Passive Active

76 There are many processes that make up the polarization curve. Fe = Fe e - 2H 2 O=O 2 +4H + +4e - H 2 O + e - = ½ H 2 +OH - H + + e - = ½ H 2

77 The Polarization Curve for 304 SS 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 H 2 Oxidation of water to O 2 Open circuit potential and current density

78 May 20, 1997OLI Systems, Inc, Kinetic Model of General Corrosion: Phenomena Partial electrochemical processes in the active state: Partial electrochemical processes in the active state: Cathodic reactions (e.g., reduction of protons, water molecules, oxygen, etc.) Cathodic reactions (e.g., reduction of protons, water molecules, oxygen, etc.) Anodic reactions (e.g., oxidation of metals) Anodic reactions (e.g., oxidation of metals) Adsorption of species on the metal surface Adsorption of species on the metal surface Active-passive transition influenced by Active-passive transition influenced by Acid/base properties of passive oxide films Acid/base properties of passive oxide films Temperature Temperature Additional species that influence the dissolution kinetics of oxide layers Additional species that influence the dissolution kinetics of oxide layers Synthesis of the partial processes according to the mixed potential theory Synthesis of the partial processes according to the mixed potential theory

79 Application Time

80 Corrosion of 316 SS in Deaerated Water o C 1886 years to lose 1 mm of metal Much better corrosion rate than 304 ss

81 Corrosion of 316 SS in Deaerated Water Difference = V

82 Application Time

83 Corrosion of 254 SMO in Deaerated Water Corrosion rate = o C > 3000 years to lose 1 mm of metal

84 Corrosion of 254 SMO in Deaerated Water Difference = 2.7 V

85 Summary in Deaerated Water Stainless 25 o C (mm/yr) Potential difference (V) SMO

86 Adding Air/Oxygen The CorrosionAnalyzer allows you to add a gas phase based only on partial pressures The CorrosionAnalyzer allows you to add a gas phase based only on partial pressures You can set the water/gas ratio You can set the water/gas ratio Species Partial Pressure (atm) N2N2N2N O2O2O2O20.21 CO WGR 0.01 bbl/scf

87 Application Time

88 304 SS in Aerated Solutions

89 304 SS in Aerated Solution The corrosion potential is greater than the passivation potential =.37 V at max O 2 Pitting will occur

90 304 SS Polarization in Aerated Water 0 ppm O 2 8 ppm O 2 Corrosion potential shifted anodically of the repassivation potential. The surface will couple galvanically with the pits to increase their rate of corrosion.

91 Application Time

92 316 SS Corrosion in Aerated Water Pitting occurs at higher oxygen concentrations =.21V at max O 2

93 Application Time

94 S31254 Corrosion in Deaerated Water Pitting should not occur

95 Stability Diagram for 316L SS

96 Stability Diagram for 316 L Nickel Only

97 Mitigation Change Alloys Change Alloys S31254 seems the best at 25 o C S31254 seems the best at 25 o C S31254 increased potential for pitting at higher temperatures S31254 increased potential for pitting at higher temperatures Cathodic Protection Cathodic Protection Shifting of potential to less corrosive potentials via a sacrificial anode. Shifting of potential to less corrosive potentials via a sacrificial anode. Analyzers do not model CP Analyzers do not model CP Polarization curves can help determine the change in potential. Polarization curves can help determine the change in potential.

98 Welcome to the CORROSION TEACH-IN Simulating Real World Corrosion Problems

99 Dealloying of Copper Nickel Alloys Scope Scope A copper-nickel pipe made of Cupronickel 30 has been preferentially dealloyed while in contact with a 26 weight percent calcium chloride brine. It appears that the nickel in the alloy has been preferentially removed. A copper-nickel pipe made of Cupronickel 30 has been preferentially dealloyed while in contact with a 26 weight percent calcium chloride brine. It appears that the nickel in the alloy has been preferentially removed.

100 Dealloying of Copper Nickel Alloys Purpose Purpose The OLI/CorrosionAnalyzer will be used to show the relative stability of nickel and copper in the cupronickel alloy in an aqueous solution. It will show that protective films were not present as originally thought. The OLI/CorrosionAnalyzer will be used to show the relative stability of nickel and copper in the cupronickel alloy in an aqueous solution. It will show that protective films were not present as originally thought.

101 Dealloying of Copper Nickel Alloys Objectives Objectives Input information into the software and perform calculations Input information into the software and perform calculations Use stability diagrams to display information about the alloy and the protective films Use stability diagrams to display information about the alloy and the protective films Change the diagrams to view different aspects of the stability of the alloy Change the diagrams to view different aspects of the stability of the alloy

102 Application: Dealloying of Copper-Nickel Alloys A cupronickel 30 pipe (30 mass % copper) was used. A cupronickel 30 pipe (30 mass % copper) was used. 26 wt % CaCl 2 solution was in contact with the pipe. 26 wt % CaCl 2 solution was in contact with the pipe. Nickel was preferentially removed. Nickel was preferentially removed. Dealloyed cupronickel pipe.

103 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 occurring? What could we do to prevent this from occurring? Which tools are available to understand this phenomenon? Which tools are available to understand this phenomenon?

104 Which Tools are Available? A Pourbaix diagram can help us determine where metals are stable. A Pourbaix diagram can help us determine where metals are stable. CorrosionAnalyzer CorrosionAnalyzer

105 Creating the First Stability Diagram We will use the CorrosionAnalyzer to create a stability diagram for this system. We will use the CorrosionAnalyzer to create a stability diagram for this system. Features of CorrosionAnalyzer diagrams Features of CorrosionAnalyzer diagrams Real-solution activity coefficients Real-solution activity coefficients Elevated temperatures Elevated temperatures Elevated pressures Elevated pressures Interactions between species and overlay of diagrams. Interactions between species and overlay of diagrams.

106 The Pourbaix Diagram

107 Application Time Time to start working with the OLI Corrosion Analyzer

108 The Pourbaix Diagram There are quite a few things to look at on this diagram. There are quite a few things to look at on this diagram. Stability field for water Stability field for water Stability fields for nickel metal and copper metal Stability fields for nickel metal and copper metal Stability fields for nickel and copper oxides Stability 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 manageable parts. We will now break down the diagram in to more manageable parts.

109 Stability Diagram Features Subsystems Subsystems A base species in its neutral state and all of its possible oxidation states. A base species in its neutral state and all of its possible oxidation states. Cu o, Cu +1, Cu +2Cu o, Cu +1, Cu +2 Ni o, Ni +2Ni o, Ni +2 All solids and aqueous species that can be formed from the bulk chemistry for each oxidation state. All solids and aqueous species that can be formed from the bulk chemistry for each oxidation state.

110 Stability Diagram Features For each subsystem For each subsystem Contact Surface Contact Surface Base metalsBase metals AlloysAlloys Films Films SolidsSolids Solid Lines Solid Lines Aqueous Lines Aqueous Lines

111 Stability Diagram Features Natural pH Natural pH Prediction based on the bulk fluid concentrations Prediction based on the bulk fluid concentrations Displayed as a vertical line Displayed as a vertical line Solids Solids All solids included by default All solids included by default The chemistry can be modified to eliminate slow forming solids. The chemistry can be modified to eliminate slow forming solids.

112 Stability Diagram Features Passivity Passivity Thin, oxidized protective films forming on metal or alloy surfaces. Thin, oxidized protective films forming on metal or alloy surfaces. Transport barrier of corrosive species to metal surface. Transport barrier of corrosive species to metal surface. Blocks reaction sites Blocks reaction sites

113 Water Stability Water can act as an oxidizing agent Water can act as an oxidizing agent Water is reduced to hydrogen, H 2 Water is reduced to hydrogen, H 2 Water can act as a reducing agent Water can act as a reducing agent Water is oxidized to oxygen, O 2 Water is oxidized to oxygen, O 2 To be stable in aqueous solution, a species must not react with water through a redox process. To be stable in aqueous solution, a species must not react with water through a redox process.

114 Water Stability

115 Water Stability – Natural Waters Surface water Ocean water Bog water Organic rich waterlogged soils Organic rich lake water Organic rich saline water

116 Copper Pourbaix Diagram Predominant species Oxidized Species Reduced Species E Independent acid and base chemistry pH independent redox pH dependent redox

117 Copper Pourbaix Diagram Stability field for base metal or alloy Stability field for passivating film Aqueous species Equilibrium between species Equilibrium between species in contact with a solid Natural pH

118 Copper 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.

119 Nickel Pourbaix Diagram No Nickel metal extends into the water stability field The solution pH is in a region where nickel is expected to corrode

120 Ni 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

121 Application Time

122 CorrosionAnalyzer Calculation

123 The oxidation reduction potential is V

124 Ni Overlaid on Cu The potential of V lies above the passivating film. Dealloying can occur.

125 Conclusions Why did dealloying occur? Why did dealloying occur? No protective film at the operating pH and oxidation/reduction potential of the process fluid. No protective film at the operating pH and oxidation/reduction potential of the process fluid. Copper lies within the region of water stability Copper lies within the region of water stability Nickel does not lie within the region of water stability Nickel does not lie within the region of water stability The presence of Cu + ions in equilibrium with copper metal promotes replating of copper metal driven by the oxidation of nickel. The presence of Cu + ions in equilibrium with copper metal promotes replating of copper metal driven by the oxidation of nickel.

126 Chemistry Standard OLI Chemistry Standard OLI Chemistry 7400 components 7400 components 9100 individual species 9100 individual species 82 Elements of the Periodic Table fully covered 82 Elements of the Periodic Table fully covered 8 additional elements partially covered.8 additional elements partially covered. Stability diagrams have access all of this chemistry Stability diagrams have access all of this chemistry

127 Chemistry Alloys Alloys 6 predefined classes supported 6 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, Mo, C and NDuplex stainless steels FCC phase - Fe, Cr, Ni, Mo, C and N User defined alloys User defined alloys

128 Limits to the Standard OLI Chemistry Aqueous Phase X H2O > o C < T < 300 o C 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

129 Limitations of Pourbaix Diagrams 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 temperature and pressure Diagram is valid only for the calculated temperature and pressure Oxide stability fields are calculated thermodynamically and may not provide an actual protective film. Oxide stability fields are calculated thermodynamically and may not provide an actual protective film. Dealloying cannot be predicted from the diagram alone. Dealloying cannot be predicted from the diagram alone.


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