Doctor of Philosophy (PhD), Ohio University, 2023, Chemical Engineering (Engineering and Technology)

Internal corrosion of transmission tubulars is a huge concern in the oil and gas industry. Corrosion inhibitors (CIs) are often considered the first step in mitigating internal corrosion due to their high efficiency and cost-effectiveness. Yet, predicting the efficiency of corrosion inhibitors, developed and tested in a laboratory environment, in operating field conditions is very challenging. In addition, the presence of corrosion residues or corrosion products on the internal surface of tubular steels can significantly affect the inhibition performance of organic corrosion inhibitors. This aspect is only rarely considered when characterizing the performance of corrosion inhibitors. Therefore, understanding their effects on corrosion inhibition is of great benefit in applying corrosion inhibitors to tackle internal corrosion issues, particularly in aging pipelines. This work mainly focuses on evaluating the corrosion inhibition and revealing the inhibition mechanisms in the absence and presence of various corrosion residues or products, commonly found in oil and gas production. The first half of this work (Chapter 5 and 6) presents a methodology for the characterization of corrosion inhibitors and proposes several innovations to an inhibition prediction model, originally based on the work of Dominguez, et al.. An inhibitor model compound, i.e., tetradecyl phosphate ester (PE-C14), was synthesized in-house and characterized to obtain necessary parameter values required as inputs for the inhibition model. The updated inhibition model could predict steady state and transient corrosion inhibition behaviors with good accuracy. The second half of the presented work (Chapter 7, 8, and 9) focuses on the effects of corrosion residue (Fe3C) and products (FeCO3 and FeS) on corrosion inhibition and advances the understanding of the associated inhibition mechanisms. The galvanic effect caused by residual Fe3C on corrosion rate and inhibition efficiency was quantitatively (open full item for complete abstract)

Committee: Marc Singer (Advisor); Srdjan Nesic (Committee Member); David Young (Committee Member); Sumit Sharma (Committee Member); Katherine Cimatu (Committee Member); Katherine Fornash (Committee Member) Subjects: Chemical Engineering; Engineering; Materials Science

Doctor of Philosophy (PhD), Ohio University, 2019, Chemical Engineering (Engineering and Technology)

The impact of fluid flow on the mechanical integrity and protectiveness of corrosion product layers formed on the surface of carbon steel pipelines is a crucial aspect of corrosion in CO2/H2S environments typically encountered in oil and gas production. Produced fluids may travel inside pipelines at velocities that can generate high shear stresses on the pipe wall. The effect of shear stress on the development of corrosion product layers, and more specifically iron sulfide layers, or the retention of already developed layers is not known. In addition, high fluid velocities generate high mass transfer rates which impact the corrosion behavior of carbon steel substrates. The effect of high mass transfer rates on the characterization of iron sulfide layers is also yet to be fully understood. The goal of this project is to explore ways to identify the individual contributing effects of wall shear stress and mass transfer rate to the development and retention of iron sulfide layers in representative flow conditions and relate this to the corrosion behavior of a carbon steel substrate. This will help characterize the protectiveness, or lack thereof, of FeS layers and enable the selection of appropriate asset integrity management program. The first part of this project focused on the development of experimental test setups, the glass cell with impeller flow and the channel cell in the single-phase flow loop, which enable representative flow conditions and control of water chemistry. The flow in these systems was characterized using electrochemical methods by developing a Sherwood correlation. The associated shear stress impacting the specimen surface was also characterized through computational fluid dynamics (CFD) techniques. The developed mass transfer correlations were used to model the experimentally determined corrosion rate results successfully. In the next part of this project, the glass cell with an impeller flow experimental setup was used to study the role (open full item for complete abstract)

Committee: Marc Singer (Advisor); Nesic Srdjan (Committee Member); Lopez Dina (Committee Member); Katherine Cimatu (Committee Member); John Staser (Committee Member) Subjects: Chemical Engineering; Chemistry; Engineering; Experiments; Fluid Dynamics; Materials Science; Mechanical Engineering

Master of Science (MS), Ohio University, 2017, Chemical Engineering (Engineering and Technology)

Iron carbonate (FeCO3) is the commonest corrosion product that forms on the surface of mild steel as a by-product of the CO2 corrosion process. This FeCO3 layer slows down further corrosion by acting as a diffusion barrier, blocking corrosive species from reaching the steel surface. However, high flow velocities, which can be common in various industrial operations, have been postulated either to lead to partial mechanical removal of FeCO3 layers or to impede the nucleation of FeCO3 crystals on the steel surface altogether. In the experimental study described herein, corrosion product formation in highly turbulent conditions was investigated with surface analysis techniques. Experiments were divided in relation to three different sets of tasks focusing on high initial saturation values, low and constant saturation values, and high velocity experiments. The first set of experiments was performed in a three electrode glass cell and rotating cylinder setup and investigated the presence/attachment/adherence of FeCO3 on the steel surface in short term experiments with high initial saturation values (S(FeCO3) = 150). The aim was to study the precipitation of FeCO3 in conditions where the bulk solution has a high concentration of ferrous ions at continuous rotational speeds, from the start to the end of each experiment. It was found that as the fluid velocity increased, there was less attachment of FeCO3, with the highest velocity of 2.0 m/s (wall shear stress of 7 Pa) showing no FeCO3 formation/attachment on the metal surface. The second task focused on controlling the pH and ferrous ion concentration in solution, in order to better mimic actual field conditions. Additionally, a controlled mass transfer setup was utilized that eliminated any non-uniformity of flow and centrifugal forces often associated with rotating cylinder working electrodes. In this set of experiments, four different materials and/or microstructures were tested, namely pure Fe (99.8%), UNS G101 (open full item for complete abstract)

Committee: Marc Singer (Advisor); Srdjan Nesic (Committee Member); Reza M. Toufiq (Committee Member); Craig Grimes (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy (PhD), Ohio University, 2016, Chemical Engineering (Engineering and Technology)

Degradation of metals associated with hydrocarbon production, combustion processes, and carbon capture is a pernicious problem in the energy sector. Consequently, laboratory simulation of CO2-containing aqueous environments is of vital importance for the study of steel corrosion. However, discrepancies between predicted, experimental, and field corrosion rate data in a midrange of operating parameters have been reported. These discoveries necessitate improving the accuracy of corrosion prediction models. Based upon preliminary experiments, iron carbonate formation near its saturation condition was identified as a major factor observed corrosion rate discrepancies. Therefore, it is imperative to conduct a systematic study to gain more understanding of corrosion product layer formation mechanisms in controlled water chemistry conditions. Small scale CO2 corrosion experiments have lacked control of pH and ferrous ion concentration, potentially creating misleading conditions related to the growth of protective iron carbonate (FeCO3). An improved experimental apparatus to study steel corrosion and associated formation of FeCO3 was developed. The design incorporates a flow-through system, enabling control of water chemistry, and newly developed sample holders that eliminate non-uniformity of flow associated with hanging samples as well as centrifugal effects associated with rotating cylinder electrodes. Corrosion experiments were conducted in a conventional glass cell and the newly developed flow-through system. Significantly different corrosion product morphologies were observed in these different systems. In controlled water chemistry conditions, iron carbide (Fe3C) was found to play a crucial role in the development of the corrosion product as it provided a favorable environment for the formation of a FeCO3 layer at the steel surface. Three different kinds of material (X65 with tempered-martensitic microstructure, C1018 with ferritic-pearlitic microstructure, an (open full item for complete abstract)

Committee: Srdjan Nesic (Advisor); Rebecca Barlag (Committee Member); Craig Grimes (Committee Member); Marc Singer (Committee Member); Yoon-Seok Choi (Committee Member); David Young (Committee Member) Subjects: Chemical Engineering

Master of Science (MS), Ohio University, 2014, Chemical Engineering (Engineering and Technology)

Several types of mild steel are used in pipeline transmission. Steels with similar mechanical properties, e.g., yield strengths, have different contents and structures of iron carbide. This leads to different corrosion behaviors and corrosion inhibitor performance. The purpose of the present study is to develop an understanding of how iron carbide layers, derived from the different microstructures of carbon steels during corrosion, affect corrosion behavior and inhibitor performance. Glass cell experiments were conducted with 2 liters of 1 wt. % NaCl as the electrolyte at the desired temperature. A magnetic stirrer, set to 200 rpm, was used to ensure a fully mixed solution as carbon dioxide gas was constantly sparged into the test electrolyte. The solution pH was adjusted to the desired pH by addition of deoxygenated 1.0 M sodium hydroxide (NaOH) or sodium bicarbonate (NaHCO3) solutions. Hydrochloric acid (HCl) was used to maintain the pH around 5.0 ± 0.1. Three steel samples were immersed in the glass cell once the pH stabilized and tests were run for 3 days. Steels with different microstructures and chemical compositions were used in separate sets of experiments. After 24 hours of each experiment, a sample was withdrawn for surface analysis. In addition, experiments show that iron carbide layer development is dependent upon the microstructure and chemical composition, particularly carbon content, of the carbon steel from which it is derived. In each case, iron carbide impairs the performance of tested imidazoline-type inhibitors. The Fe3C developed from X65 (0.14 wt. % C) steel (ferrite-discrete cementite) has significantly more effect (i.e. decreases the inhibition efficiency) on the performance of inhibitors than the Fe3C developed from other types of steel. The performance of the inhibitor on X65 (0.05 wt. % C) spheroidized was less impaired than the performance of the inhibitor on other types of steel. In addition, the performance of the inhibit (open full item for complete abstract)

Committee: David Young (Advisor) Subjects: Chemical Engineering