c 2015 AARON JOSEPH STENTA ALL RIGHTS RESERVED

242 Pages·2015·2.61 MB·English

c 2015
(cid:13)
AARON JOSEPH STENTA
ALL RIGHTS RESERVED
SPECIES-DEPENDENT MODELING OF CREVICE CORROSION SYSTEMS
A Dissertation
Presented to
The Graduate Faculty of The University of Akron
In Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy
Aaron Joseph Stenta
August, 2015
SPECIES-DEPENDENT MODELING OF CREVICE CORROSION SYSTEMS
Aaron Joseph Stenta
Dissertation
Approved: Accepted:
Advisor Department Chair
Dr. Curtis Clemons Dr. Timothy Norfolk
Committee Member Acting Dean of the College
Dr. Gerald Young Dr. Rex Ramsier
Committee Member Interim Dean of the Graduate School
Dr. Kevin Kreider Dr. Chand Midha
Committee Member Date
Dr. Scott Lillard
Committee Member
Dr. Chelsea Monty
Committee Member
Dr. Graham Kelly
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ABSTRACT
A species dependent, one-dimensional mathematical model is developed to describe
localized crevice corrosion applications. An asymptotic procedure taking advantage
of disparity in length scales is used to derive the governing system. The equations
are rotated to eliminate bulk reactions, and formulate a boundary value problem for
numerical solution. This research extends previous 1D well-mixed approaches [1, 2]
to non well-mixed electrolytes, and explores its capabilities. To create this concen-
tration dependent crevice corrosion model with damage evolution we propose: (i) 1D
simplified configurations that have government and industrial corrosion applications;
(ii) multiple formulations of 1D rotated systems that simplify the complex system of
higher order nonlinear equations; (iii) a numerical procedure that is efficient and open
source; (iv) the use of standard practice experimental inputs to predict Ni-625 crevice
corrosion metal dissolution that validates experimental time history damage profiles;
(v) a COMSOL 2D time-dependent finite element model to assist and validate the 1D
modeling efforts; (vi) to benchmark the numerical procedure with analytical solutions
and known literature; (vii) localized modeling insight to the scientific corrosion com-
munity that may allow for the development of commercially available, user-friendly
software packages, further experimental efforts, and increased scientific knowledge of
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corrosion phenomena; and (viii) a generalized modeling procedure and solution for
application to additional material systems.
The Ni-625 modeling effort includes a three-stage model to determine the
spatial andtemporal potential, current, ionic species, anddamage profiles in seawater
crevice corrosion applications. Stage one is oxygen depletion inside the crevice, stage
two is the development of a critical crevice solution (induction stage), and stage
three is long-term agressive dissolution that is consistent with a nearly well mixed,
IR drop controlled crevice system. In stage one deoxygenation allows separation of
the anodic and cathodic sites. In stage two local initiation occurs at the crevice tip
that diffuses towared the crevice mouth. Minimal dissolution occurs in stage two
and complete initiation occurs when the total anodic current is such that the critical
IR drop is observed. In stage three the crevice is saturated at or near the critical
crevice solutionandmetal salt precipitates allowstable crevice corrosionpropagation.
The key inputs to the three stage model are concentration dependent polarization
curves and non-equilibrium hydrolysis reaction data. The analytical solutions and
2D COMSOL modeling efforts are used to validate the proposed 1D approach for
simplified systems leading up to the complex Ni-625 system. All results agree under
a thin-film approximation. Further, we show that with appropriate experimental
inputdata, andknowledge fromsolutionofthespecies-dependent system, thedamage
evolution well-mixed model provides comparable results.
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ACKNOWLEDGEMENTS
The past four years of my academic career, including my MS and PhD programs,
have been quite memorable. Throughout the entire process, all of my advisors and
professors have supported me and my work, and treated me not as a student, but as
fellow colleague. I am greatly appreciative of everything they have done, and I hope
that all of them can say the same about my contribution to them and the university.
I especially would like to thank my dissertation director Dr. Young, whom
convinced me to join UAkron and the corrosion modeling team from day one. To-
gether, with Dr. Clemons and Dr. Kreider, this group of mathematicians has been
a tremendous pleasure to work with. The communication and team effort on all
projects is always maintained to great extent. The lessons learned and knowledge
gained, outside of coursework and research, far surpass what anyone could have ex-
pected. I am confident that, because of their efforts, I will accelerate in my career
opportunities and be a valuable asset to any organization.
Additionally, the members of the corrosion squad have been a pleasure to
work with for all of the academia research that I participated in, all of my engineering
coursework, and outside of the classroom on a personal and professional level. The
few most direct influences that I would like to acknowledge include, Dr. Lillard, Dr.
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Payer, Dr. Monty, and Paul Young. Outside of the chemical engineering faculty and
fellowstudents, Dr. KellyandDr. Povitskyofthemechanical engineeringdepartment
were a pleasure to work with. They helped me to broaden my applied mathematics
background through additional engineering applications. I would also like to thank
Dr. Golovaty for his valuable discussions throughout this research and support with
COMSOL related modeling efforts.
Outside of my academia experiences I would like to thank my previous work
colleaguesatAirForceResearchLaboratory,Dr. Dudis, Dr. Hunter, andDr. Juzuko-
nis, fortheopportunitytoparticipateinvariousDODresearchprojects. Theseoppor-
tunities allowed me to enhance my professional career far beyond what was possible
through academia alone. Finally, I am greatly appreciative of all of my family and
friends that have supported me and pushed me to never give up throughout my entire
academic career. Without them I truly would not be where I am today.
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TABLE OF CONTENTS
Page
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii
CHAPTER
I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 General Problem Statement and Motivation . . . . . . . . . . . . . . 1
1.2 General Understanding of Crevice Corrosion . . . . . . . . . . . . . . 3
1.3 Experimental Background and Ni-625 Literature Review . . . . . . . 6
1.3.1 Ni-625 Thermodynamics and Passivity Stability . . . . . . . 7
1.3.2 In-situ Crevice Profile Measurements . . . . . . . . . . . . . 9
1.3.3 Crevice Corrosion Mechanisms . . . . . . . . . . . . . . . . 11
1.3.4 Experimental Polarization Curves . . . . . . . . . . . . . . 14
1.3.5 Potentio-static Measurements (Total Current) . . . . . . . . 21
1.4 Lillard/Salgado Experimental Support . . . . . . . . . . . . . . . . . 24
1.5 Modeling Background . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.6 Model Definition and Formal Hypothesis . . . . . . . . . . . . . . . . 33
II. MATHEMATICAL FORMULATION . . . . . . . . . . . . . . . . . . . . 41
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2.1 Governing System of Equations . . . . . . . . . . . . . . . . . . . . . 41
2.2 Asymptotic Reduction of Order - 1D Formulation . . . . . . . . . . . 45
2.3 Rotation of the 1D Equations (Preparation for bvp5c): . . . . . . . . 49
2.3.1 Two Species System - No Bulk Reactions . . . . . . . . . . 54
2.3.2 Three Species System - No Bulk Reactions . . . . . . . . . 56
2.3.3 Six Species Engelhardt System . . . . . . . . . . . . . . . . 59
2.3.4 Five Species Ni-625 Lillard System . . . . . . . . . . . . . . 64
2.4 Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
III. ANALYTIC SOLUTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.1 Two Species System - No Bulk Reactions . . . . . . . . . . . . . . . 75
3.2 Three Species System - No Bulk Reactions . . . . . . . . . . . . . . . 76
3.3 Analytical Bulk Solution . . . . . . . . . . . . . . . . . . . . . . . . . 78
3.4 Migration and Diffusion Dominated Systems . . . . . . . . . . . . . . 82
IV. NUMERICAL FORMULATIONS AND PROCEDURES . . . . . . . . . 84
4.1 1D System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
4.1.1 Matlab bvp5c . . . . . . . . . . . . . . . . . . . . . . . . . . 84
4.1.2 COMSOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.2 Interior/Exterior Species . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.3 Interior Species/Exterior Well-Mixed . . . . . . . . . . . . . . . . . . 89
4.4 Diffusion Dominated Systems . . . . . . . . . . . . . . . . . . . . . . 91
4.5 Discretization of the Damage Equation . . . . . . . . . . . . . . . . . 94
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4.6 Higher Dimensional Governing System . . . . . . . . . . . . . . . . . 94
4.6.1 Bulk Reactions . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.7 Numerical Parameters and Conditions . . . . . . . . . . . . . . . . . 97
V. RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
5.1 Two Species System . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
5.2 Three Species System . . . . . . . . . . . . . . . . . . . . . . . . . . 109
5.3 Six Species System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
5.3.1 Interior/Exterior Results . . . . . . . . . . . . . . . . . . . 114
5.4 Five Species Lillard System . . . . . . . . . . . . . . . . . . . . . . . 118
5.4.1 Experimental Input Data . . . . . . . . . . . . . . . . . . . 119
5.4.1.1 GeneralImplementation ofSpecies-Dependent Po-
larization Curves . . . . . . . . . . . . . . . . . . . . 124
5.4.1.2 Implementation of HCl Simulated Polarization Curves 125
5.4.2 Experimental Corrosion History . . . . . . . . . . . . . . . 127
5.4.3 Stage 1 - Deoxygenation . . . . . . . . . . . . . . . . . . . . 137
5.4.4 Stage 2 - Metal Ion Diffusion - Initiation . . . . . . . . . . . 141
5.4.5 Stage 3 - CCS Crevice - Damage Evolution . . . . . . . . . 151
5.4.6 Additional Ni-625 Investigations . . . . . . . . . . . . . . . 174
5.5 General Approach for Additional Material Systems . . . . . . . . . . 183
VI. CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
6.1 Summary of Contributions/Findings . . . . . . . . . . . . . . . . . . 191
6.2 Future Work and Recommendations . . . . . . . . . . . . . . . . . . 194
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