Corrosion Simulation. OLI Simulation Conference A. Anderko, G. Engelhardt and M.M. Lencka

Transcription

1 OLI Simulation Conference 2010 Corrosion Simulation Think Simulation! Harnessing the power of the OLI Engine A. Anderko, G. Engelhardt and M.M. Lencka

2 General and localized corrosion models Single-phase flow in electrochemical models Electrochemistry of metal solution interface Fluid flow effects Cr / Mo grain boundary depletion model AQ and MSE thermodynamic models + stability diagrams Chemistry / corrosion thermodynamics Corrosion modeling Alloy microstructure effects Probabilistic aspects of propagation Reactive transport / propagation of localized phenomena Structure of corrosion modeling Extreme value statistics Standalone models for crevice corrosion, SCC, corrosion fatigue (not in CA)

3 Scope Review of corrosion simulation models Progress in the general and localized corrosion models Corrosion mechanisms for Cu and Cu-Ni alloys Localized corrosion of duplex alloys including the effect of heat treatment Algorithms for propagation of corrosion Propagation of crevice corrosion Further development plans

4 Electrochemical model for predicting general corrosion Partial electrochemical processes Cathodic reactions (e.g., reduction of protons, water molecules, oxygen, etc.) Anodic reactions (e.g., oxidation of metals) Adsorption phenomena Passive dissolution and active-passive transition as a function of Acid/base properties of passive oxide films Temperature Additional aggressive or inhibitive species Synthesis of the processes using mixed potential theory

5 Potential Potential Potential Potential Predicting localized corrosion: Repassivation and corrosion potentials versus environmental conditions E rp E rp Ecorr Ecorr Chloride Localized corrosion E rp Ecorr Temperature Localized corrosion E c orr E rp Localized corrosion Inhibitor Oxidant Localized corrosion

6 Electrochemical models for general and localized corrosion Metals Carbon steel Stainless steels: 13Cr, 304, 316, 254SMO Nickel-base alloys: 22, 276, 625, 825, 600, 690, and Ni Aluminum Copper

7 General corrosion of Cu and Cu-Ni alloys Mechanistic aspects Proximity of the reversible potential plays a key role Both oxidation of Cu and reduction of Cu ions need to be considered In the presence of Cl - or other complexing ions: Anodic dissolution is controlled by formation and mass transfer of complexes such as CuCl 2 - Mass transfer has a strong effect on anodic dissolution Anodic dissolution may lead to the formation of salt layers (e.g., CuCl (s) ), which may lead to a plateau of current density [Cl - ] 0 Metal CuCl [Cl - ] [CuCl 2- ] [Cl - ] [CuCl 2- ]

8 Corr. Rate (mm/y) Corrosion rate in nearly-pure water ph Jacobs and Edwards (2000) 295 K, 6.5 ppm O2 Pehkonen et al. (2002) 296 K, 6.9 ppm O2 Pehkonen et al. (2002) 296 K, 0.7 ppm O2 Calc, 298 K, 6.9 ppm O2 Calc, 298 K, 0.7 ppm O2 Corrosion rate nearly parallels the stability diagram Cu is passive only in the neutral to alkaline ph range It becomes very low in the passive range In the passive range, it is weakly dependent on O 2 concentration but this dependence increases at lower and higher ph

9 Corr. Rate (mm/y) Corr. Rate (mm/y) m H 2 SO m CuSO 4 (Cu 2+ and O 2 reduction) 0.5m H 2 SO 4 (O 2 reduction only) rpm Sorokin and Romasenko (1974) 293 K, 0.51 m H2SO4, air Sorokin and Romasenko (1974) 293 K, 0.51 m H2SO4, 0.5 m CuSO4, air 293 K, 0.51 m H2SO4, cal 293 K, 0.51 m H2SO4, 0.5 m CuSO4 cal Corrosion rate in aerated H 2 SO 4 Strong effect of flow conditions on both the cathodic and anodic process O2 (vol%) ASM Handbook (1987) 297 K, m H2SO4 Calc, static Strong effect of oxygen concentration Oxygen-free H 2 SO 4 is very weakly corrosive (H + reduction plays a minor role)

10 Ecorr (V/SHE) Corr. Rate (mm/y) Dhar et al. (1985) 295 K, m NaCl, air Bjorndahl and Nobe (1984) 298 K, m NaCl, air Bjorndahl and Nobe (1984) 298 K, m NaCl, deoxygenated Calc, 295 K, m NaCl, air Calc, 298 K, m NaCl, air Calc, m NaCl, dearated (0.8ppm O2) rpm Corrosion rate and potential in chloride solutions Chlorides reduce the corrosion potential because of their effect on anodic dissolution Strong effect of aeration King et al.(1995) 298 K, 1.02 m NaCl, M O2 King et al.(1995) 298 K, 1.02 m NaCl, M O2 King et al.(1995) 298 K, 1.02 m NaCl, M O2 King et al.(1995) 298 K, 1.02 m NaCl, M O2 King et al.(1995) 298 K, 0.1 m NaCl, M O2 Calc, 298 K, 1.02 m NaCl, M O2 Calc, 298 K, 1.02 m NaCl, M O2 Calc, 298 K, 1.02 m NaCl, M O2 Calc, 298 K, 1.02 m NaCl, M O2 Strong effect of flow on both corrosion rate and potential rpm Calc, 295 K, m NaCl, ph 6.5, air

11 Erp(SHE) Erp (SHE) Erp (V/SHE) m Cl - m Cl m Cl t=23c, ph=9, borate t=60c, ph=9, borate t=95c, ph=9, borate t=23c, ph=11 t=23c, ph=11, borate t=60c, ph=11 t=95c, ph=11 Cal, t=23c, borate Cal, t=60c, borate Cal, t=95c, borate Cal, t=23c, no borate Cal, t=60c, no borate Cal, t=95c, no borate t=25c, ph= t=23c, ph=9, buffer t=60c, ph=9, buffer t=23c, ph=11 t=60c, ph=11 t=95c, ph=11 t=25c, ph=10.3 t=25c, ph= Cal, t=23c, borate Cal, t=60c, borate Cal, t=95c, borate Cal, t=23c, no borate Cal, t=60c, no borate Cal, t=95c, no borate 303 K, m HCO3, m SO4 303 K, m HCO3, m SO4 303 K, m HCO3, m SO4 303 K, m HCO3, m SO4 368 K, m HCO3, m SO4 368 K, m HCO3, m SO4 368 K, m HCO3, m SO4 368 K, m HCO3, m SO4 Calc. 303 K, m HCO3, m SO4 Calc 303 K, m HCO3, m SO4 Calc 303 K, m HCO3, m SO4 Calc 303 K, m HCO3, m SO4 Calc 368 K, m HCO3, m SO4 Calc 368 K, m HCO3, m SO4 Calc 368 K, m HCO3, m SO4 Calc 368 K, m HCO3, m SO4 Repassivation potential of Cu and Cu-Ni alloys CuNi7030 CuNi9010 Cu In the low-slope region, the E rp vs. Cl - relationship is exactly the same This is in contrast with Fe-Ni-Cr-Mo-W alloys, in which E rp is a strong and complex function of alloy composition in all regions This indicates a common controlling mechanism

12 E rp measurements of Cu70Ni30 in 0.05 M Cl - E rp E corr No hysteresis in the 2 nd and 3 rd cycle This indicates deactivation at the measured E rp hysteresis would indicate oxide formation Deactivation is controlled by Cu dissolution because Cu has a much higher reversible potential than Ni The E rp model can reproduce this behavior because it includes the dissolution mediated by the formation of chloride complexes It still accounts for the reformation of oxides but at lower chloride concentrations

13 How predictive is the localized corrosion model? A generalized correlation has been developed for predicting E rp for Fe-Ni-Cr-Mo-W-N alloys as a function of alloy composition Application to 0.6 duplex alloy 2205: Only 3 experimental data points are available However, the correlation gives us a complete prediction Erp (SHE) a Cl - 60 C, exp 150 C, cal 95 C, cal 60 C, cal 23 C, cal

14 E (SHE) Critical crevice corrosion temperature (CCT) test CCT can be tested in a 6% FeCl 3 solution E corr is controlled by the reduction of Fe(III) ions There are no E corr data for alloy 2205 in Fe(III) but it should be very similar on similar alloys The predicted CCT is 19 C The experimental CCT is 18 C Predicted critical crevice temperature Erp, 6% FeCl3 Ecorr, 6% FeCl t, C

15 Can we predict the susceptibility to localized corrosion of alloy phases with altered composition? Sensitization of duplex alloys leads to the formation of M 23 C 6 carbides, followed by decomposition of ferrite into secondary austenite and sigma phase Secondary austenite is depleted with respect to Cr This creates a wide, asymmetric Cr depletion zone Preferential corrosion in the ferrite phase: Austenite Ferrite + sigma + austenite

16 Mo i Cr i Ni i duplex: Heat treatment increases susceptibility to localized corrosion Secondary austenite i Boundary Primary austenite nm The depletion profile measured on both sides of the primary/secondary austenite boundary (thermally aged at 700 C for 5h) Erp (SHE) / V a Cl mill-annealed 700 C, 5 h 700 C, 24 h Cal., annealed Cal., 700 C, 5 h Cal., 700 C, 24 h The Cr-depleted area is more susceptible to localized corrosion and controls E rp E rp can be predicted based on experimental secondary austenite composition

17 Progress in modeling propagation of localized attack: Crevice corrosion Electrolyte 0 Insulator w(x) x ds dx x+dx w(x+dx) Metal crevice L x What crevice geometries are susceptible to localized corrosion? What is the critical depth of the crevice (i.e., the minimum depth below which crevice corrosion will not occur)? Determining factors: Acidification within crevice Ohmic (IR) drop, which may cause the crevice walls to be in the active state even though the rest of the metal is passive

18 Potential drop within crevice More than one steadystate (stable or metastable) solutions are possible Strong effect of conductivity and crevice geometry E 0 (mv SCE ) Potential at the crevice mouth S/m 3.0 S/m E L,1 E L,2 E L,3 E 0 =E L L = 10 mm w = 0.5 mm E L (mv SCE ) Potential at the crevice tip

19 Calculated crevice gap as a function of time Crevice gap (mm) Crevice propagation after 6, 12, and 24 h E m = 750 mv sce E L,0 = -545 mv sce Crevice corrosion often propagates the most at intermediate distance from the crevice mouth Ohmic drop is the direct reason This agrees with experiments Distance into the crevice (mm)

20 Summary Technology in Corrosion Analyzer Stability diagrams Electrochemical kinetics of general corrosion Prediction of localized corrosion using repassivation potential Prediction of Cr/Mo grain boundary depletion and its effect on localized corrosion Extreme value statistics for time evolution of corrosion Recent developments General and localized corrosion of base alloys Corrosion mechanisms for Cu and Cu-Ni alloys Effect of heat treatment on localized corrosion Implementation of heat treatment effects in Corrosion Analyzer Progress in algorithms for propagation of localized corrosion

21 Future Development Short-term Implementation of the general corrosion model for CuNi9010 and CuNi7030 Implementation of the model for alloy 2205 Long-term Model for general and localized corrosion in mixed-solvent environments The same range of applicability as the MSE model Modeling passivity in the presence or absence of various oxygen donors Modeling salt film formation Effects of solvent on electrochemical reactions