Sweet Corrosion Precursors: A Surface Science Approach

Abstract

It is well-known that oil production remains as the world’s leading energy source. Economics drive oilfield equipment to be largely fabricated from carbon steel, which performs well mechanically, but is highly susceptible to corrosion. Therefore, corrosion in oilfield facilities is of enormous concern, not only due to the huge economic costs (with an estimated annual cost of $1.372 billion) but also the health and environmental risks associated with the potential failure of equipment. In spite of the significant effort expended to keep oilfield corrosion under control and mitigate it, surprisingly little is known about the mechanisms underpinning pertinent corrosion phenomena, especially in the initial stages of the process. This lack of mechanistic insight is restricting progress, including understanding the lifecycle of potentially protective CO2-induced corrosion scales. Given the above, the goal of this research aims to address this lack of knowledge and develop a molecular level understanding of CO2-induced corrosion scale initiation. From an engineering perspective, such data will facilitate more knowledge-based design of strategies to control oilfield corrosion. In contrast to the other work in this area, a surface science approach is being adopted, i.e. undertaking studies on model single crystal substrates. More specifically, in an attempt to address more realistic conditions beyond UHV studies, STM LEED and AES were employed to study the interaction of CO2 and H2O with Fe(110), under near ambient pressure conditions (NAP) and at high temperature. When simultaneously dosing both CO2(g) and H2O(g) under NAP conditions, the interaction with the metallic surface was observed to be dominated by the H2O chemistry, which has not been previously reported. Moreover, highly ordered overlayers solely composed of chemisorbed O atoms were obtained after all the exposures performed, which suggests that the dissociation of both species is catalysed on the Fe (110) surface. Regarding the chemical characterization, Hard X-ray Photoelectron Spectroscopy (HAXPES) was also employed to probe “true” bulk composition unhindered by surface contributions in 2 model single-crystal iron oxides: α-Fe2O3(0001) and Fe3O4(110). This allowed more reliable interpretations of spectra from complex iron systems, like the solid/liquid interface studied in the NAP-XPS experiment. We found that the intrinsic asymmetry displayed by the O 1s core level of the Fe3O4(110) is not related to any surface defect, as previously reported, but to energy losses from the excitation of electrons into the conduction band immediately above the Fermi edge. Finally, the NAP- XPS revealed that both H2O (l) and the CO2 are required to form the new carbonate- related adsorbates on top of the polycrystalline Fe sample, which are suggested to be the intermediates that drive the cathodic reaction in sweet corrosion. Moreover, these new weakly-bonded species do not appear if the thickness of this water layer significantly increases, suggesting that the Fe substrate surface catalyses the formation of these species.

Date of Award	22 Jun 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Christopher Muryn (Co Supervisor) & Rob Lindsay (Main Supervisor)