Effect of Calcium on the Formation and Protectiveness of the Iron Carbonate Layer in CO2 Corrosion A thesis presented to the faculty of the Russ College of Engineering and Technology of Ohio University In partial fulfillment of the requirement for the degree Masters of Science Saba Navabzadeh Esmaeely August 2013 © 2013 Saba Navabzadeh Esmaeely. All Rights Reserved 2 This thesis entitled Effect of Calcium on the Formation and Protectiveness of the Iron Carbonate Layer in CO2 Corrosion by SABA NAVABZADEH ESMAEELY has been approved for the Department of Chemical and Biomolecular Engineering and the Russ College of Engineering and Technology by Srdjan Nesic Professor of Chemical and Biomolecular Engineering Dennis Irwin Dean, Russ College of Engineering and Technology 3 ABSTRACT NAVABZADEH ESMAEELY, SABA, M.S., August 2013, Chemical and Biomolecular Engineering Effect of Calcium on the Formation and Protectiveness of the Iron Carbonate Layer in CO2 Corrosion (123 pp.) Director of Thesis: Srdjan Nešić 2+ Due to the isostructurality between calcite (CaCO3) and siderite (FeCO3), the Ca 2+ ion incorporates in the hexagonal FeCO3 lattice and vice versa the Fe ion incorporates 2+ in the hexagonal CaCO3 lattice. Thus, in aqueous CO2 environments, where both Ca 2+ and Fe are present, such as in gas reservoirs or deep saline aquifers, following CO2 injection, mixed metal carbonates with the formula FexCayCO3 (x+y=1) will be expected to form. This will likely have implications for corrosion, so that corrosion product layers will have the potential to be inhomogeneous, with behavior that deviates from that of 2+ pure FeCO3. In the present study, the effect of Ca on the CO2 corrosion behavior of mild steel was investigated with different concentrations of Ca2+ (10, 100, 1,000 and 10,000 ppm). Electrochemical methods (open circuit potential (OCP) and linear polarization resistance (LPR) measurements) were used to measure the corrosion rate with time. Surface analysis techniques (scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD)), were used to characterize the morphology and composition of the corrosion products. The results showed that with low concentrations of Ca2+ (10 and 100 ppm), the corrosion rate decreased with time due to the formation of protective FeCO3 and/or FexCayCO3 (x + y 4 =1). However, the presence of high concentrations of Ca2+ (1,000 and 10,000 ppm) resulted in the change of corrosion product from protective FeCO3 to non-protective CaCO3 and FexCayCO3 (x + y =1) and an increasing corrosion rate with time. While the general corrosion rate was high for both 1,000 and 10,000 ppm Ca2+, surface analysis data revealed that localized corrosion was observed in the presence of 10,000 ppm Ca2+. 2+ - Since Ca was added in the tested conditions as CaCl2, the possible effect of Cl on the non-uniform attack was studied by testing with the equivalent concentration of Cl- using a NaCl solution. However, the result showed that Cl- had no effect on the non-uniform corrosion behavior. Although non-uniform corrosion behavior may be due to many factors, an increasing number of experimental results link the non-homogeneous corrosion product layer to non-uniform corrosion attack. The determination of the relative 2+ 2+ concentrations of Ca and Fe in FexCayCO3 is of key importance in understanding and predicting the relative properties and stabilities of such mixed metal carbonates. Using Bragg’s law and equations to relate interplanar spacings to unit cell parameters, X-ray 2+ diffraction (XRD) data can yield precise values for incorporation of Ca in FexCayCO3 solid solutions. The results show that as the concentration of Ca2+ in the structure of this mixed metal carbonate increases the general corrosion rate increases. Non-uniform 2+ corrosion behavior was observed with 90% concentration of Ca in the FexCayCO3 structure. 1 1 Elements of this abstract have been reproduced in a paper that was presented at NACE 2013 conference. 5 DEDICATION To Parivash Jahanshahi and Heshmat Navabzadeh Esmaeely (my parents) Arash Mojab (my husband) And to All those Iranians who are struggling for freedom and peace in Iran 6 ACKNOWLEDGEMENTS I would like to sincerely thank my advisor Prof. Srdjan Nešić for his constant support, guidance and understanding during my Masters study at Ohio University. I have always been inspired by his generosity in teaching and supporting his students in all aspects. Under his supervision I have been taught challenges are there to be solved, not to stop me. I would also like to thank Dr. David Young for supporting me and believing in me even when I did not believe in myself. His friendship kept me sane. I gratefully appreciate his advice on the chemistry aspects of my research. I would like to take the chance to thank Dr. Yoon-Seok Choi and Mr. Bruce Brown, my project leaders for their invaluable suggestions on my project. The assistance and help of the technicians and especially the lab engineer Mr. Cody Shafer at the Institute for Corrosion and Multiphase Technology (ICMT) is highly appreciated. I would like to express my appreciation to the committee members, Prof. Kevin Crist and Prof. Lauren McMills for their agreement to be my thesis committee. I would like to thank the students and staff at ICMT for making me feel supported. At the end I express my appreciation for the department of Chemical and Biomolecular Engineering for the financial support of my study. 7 TABLE OF CONTENTS Page Abstract ............................................................................................................................... 3 Dedication ........................................................................................................................... 5 Acknowledgements ............................................................................................................. 6 List of tables ........................................................................................................................ 9 List of figures .................................................................................................................... 10 Chapter 1: Introduction ..................................................................................................... 19 Chapter 2: Literature review ............................................................................................. 21 CO2 Corrosion of mild steel in high pressure CO2 ....................................................... 24 Effect of the brine composition ..................................................................................... 25 Effect of Ca2+ on corrosion ........................................................................................... 30 Chapter 3: Research objectives and test matrices ............................................................. 33 Project objectives and hypotheses ................................................................................. 33 Experimental setup and test matrixes ............................................................................ 33 Weight loss measurement procedure............................................................................. 41 Pitting corrosion rate measurement procedure .............................................................. 41 Effect of calcium concentrations on corrosion .............................................................. 42 Effect of pH fluctuation on corrosion in the presence of calcium ................................ 61 8 Chloride or calcium; which one is to be blamed for localized attack ........................... 82 Effect of initial pH at 10,000 ppm Ca2+ on corrosion behavior .................................... 93 Quantitative XRD analysis .......................................................................................... 108 Chapter 5: Conclusions and future work ........................................................................ 113 Conclusions ................................................................................................................. 113 Future work ................................................................................................................. 113 References ....................................................................................................................... 115 Appendix 1: Kinetic study of the scale formation .......................................................... 121 9 LIST OF TABLES Page Table 1. Brine compositon (in mg/kg) of Rose Run, Clinton, Mt. Simon and Grand Rapids deep saline aquifers [1]. ........................................................................................ 27 Table 2. Chemical composition carbon steel CS1018 (%, balance Fe). ........................... 33 Table 3. Experimental parameters for electrochemical measurements. ........................... 35 Table 4. Test conditions. ................................................................................................... 36 Table 5. Test matrix for low to high Ca2+ concentrations. ................................................ 37 Table 6. Test matrix for the effect of Cl- . ......................................................................... 38 Table 7. Test matrix for the effect of initial pH. ............................................................... 39 Table 8. Corresponded data to the tests with 10,000 ppm Ca2+ with different initial pH. ........................................................................................................................................