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The Effect of Turbulent Flow on Corrosion of Mild Steel in High Partial CO2 Environments

Mohammed Nor, Azmi
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1363706400

Abstract Details

2013, Doctor of Philosophy (PhD), Ohio University, Chemical Engineering (Engineering and Technology).
The need to develop natural gas hydrocarbon gas fields that have high concentrations of CO2 necessitates technical evaluation of the feasibility of using carbon steels as infrastructure material particularly as its use would positively impact the economic viability of such development projects. This requires a suitable CO2 corrosion prediction model. However, the upper pressure limit of existing CO2 corrosion prediction models is 20 bar, well below the encountered subcritical and supercritical pressures (73.4 bar). Employing existing models for the design of the production assets would lead to over prediction, resulting in over design and high costs. A further requirement for the development of a suitable corrosion model for high CO2 partial pressure environments was the inclusion of the effect of flow. Therefore, this study focused on three parameters that might affect the flow-sensitivity of CO2 corrosion: CO2 partial pressure, pH, and temperature. To accomplish the objectives, two types of flow geometries were used to study flow-sensitive corrosion at elevated CO2 partial pressure and high temperature environment: rotating cylinder electrode (RCE) and thin-channel flow cell (TCFC). Since TCFC was a new flow apparatus, the mass transfer behavior of TCFC was characterized using limiting current density technique. In the experiment, the limiting current density of API 5L X-65 carbon steel was measured at various velocities in 1 wt% NaCl electrolyte at pH 3.0 for each of the test temperatures of 30o C and 50o C. The data showed good correlation with the mass transfer correlation of Sleicher and Rouse for a smooth pipeline. This established TCFC as being suitable for study of flow-sensitive corrosion. In RCE experiments, the effect of pH (pH 3.0 to pH 5.0) was studied at CO2 partial pressure of 10 bar and temperature of 25o C and 50o C in 1 wt% NaCl electrolyte. The findings indicated that the increase in pH led to the decrease in corrosion rate. Most importantly, the findings revealed that the effect of pH on flow-sensitivity as compared against a mass transfer correlation was not considerable even when the concentration of hydrogen ions was relatively high. This was attributed to the dominant effect of flow-insensitive chemical-reaction controlled hydration of dissolved CO2 that precedes the direct reduction of carbonic acid. The effect of temperature (25o C, 50o C, and 80o C) at CO2 partial pressure of 10 and 80 bar and at pH 3.0 and pH4.0 showed that the increase in temperature considerably accelerated CO2 corrosion rates. However, the increase in temperature even at 80o C did not seem to significantly enhance the flow-sensitivity of CO2 corrosion. This again may be attributed to the dominance of direct reduction of carbonic acid that was limited by the slow hydration of aqueous CO2. The effect of increasing CO2 partial pressure (10, 40, and 80 bar) as carried out at pH 3.0 and 50o C was to enhance CO2 corrosion rate due to the increase in the direct reduction of carbonic acid as its concentration increased. However, the increase was not linear and became relatively smaller as the CO2 partial pressure increased further probably due to the saturation of adsorbed carbonic acid on the steel surface. In fact, in the RCE experiments, the corrosion rate decreased at high CO2 partial pressure and temperature (80 bar and 80o C). However, this was more due to the formation of protective iron carbonate layers, resulting from the change in water chemistry. Nevertheless, the TCFC experiments with a larger volume of test solution produced more realistic results with no iron carbonate layer formation at 80 bar and 80o C test conditions. Even in the absence of iron carbonate layers in the TCFC, the flow-sensitivity of CO2 corrosion at elevated CO2 partial pressure was still relatively low due to the dominance of flow-insensitive hydration of aqueous CO2. Notwithstanding this, the fact that the corrosion rates at low temperature (25o C) in the RCE and TCFC with similar mass transfer coefficients correlated well indicated that CO2 corrosion was geometry-independent.
Srdjan Nesic, Prof. (Advisor)
Howard Dewald, Prof. (Committee Member)
Jeffrey Rack, Prof. (Committee Member)
Dusan Sormaz, Assoc. Prof. (Committee Member)
David Young, Dr (Committee Member)
215 p.
Chemical Engineering
Supercritical CO2; thin-channel flow cell; rotating-cylinder electrode; high CO2 corrosion; modeling; mass-transfer characterization

Recommended Citations

Citations

  • Mohammed Nor, A. (2013). The Effect of Turbulent Flow on Corrosion of Mild Steel in High Partial CO2 Environments [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1363706400

    APA Style (7th edition)

  • Mohammed Nor, Azmi. The Effect of Turbulent Flow on Corrosion of Mild Steel in High Partial CO2 Environments . 2013. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1363706400.

    MLA Style (8th edition)

  • Mohammed Nor, Azmi. "The Effect of Turbulent Flow on Corrosion of Mild Steel in High Partial CO2 Environments ." Doctoral dissertation, Ohio University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1363706400

    Chicago Manual of Style (17th edition)

ohiou1363706400
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© 2013, some rights reserved.Creative Commons License The Effect of Turbulent Flow on Corrosion of Mild Steel in High Partial CO2 Environments by Azmi Mohammed Nor is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by Ohio University and OhioLINK.