A Preliminary Molecular Simulation Study on the Use of HS⁻ as a Parameter to Assess the Effect of Surface Deposits on the SRB-Initiated Pitting on Metal Surfaces

ABSTRACT

Studies in microbiologically influenced corrosion (MIC) have reported on the effects of pre-corrosion surface deposits on the localized pitting which occurs on metals. But due to the complexity and heterogeneity of these deposits, which include biofilms, it is necessary to investigate how the components of these deposits and the conditions therein influence the formation of pits on the metal surfaces. To gain a better understanding of the occurrence and growth of pits under these deposits, it is imperative to consider their interactions with the metal surface at the atomistic level. In this work, molecular modelling is used to study these interactions, with the focus being on parameterizing the role of HS^- in microbiologically influenced pitting. The bond length of HS^- is used as a predictive parameter in the molecular model to study the MIC interface. It is observed that changes in the HS^- bond length denote HS^- reactivity and the subsequent production of sulfides which are the main by-products of MIC. This study also shows how changes in temperature impact HS^- reactivity and thus MIC activity.

INTRODUCTION

Since microbiologically influenced corrosion (MIC) was identified as one of the main threats to asset integrity management in the oil and gas industry, numerous studies have been done to understand the reactions that occur at the corrosion interface.^1-4 While these studies have contributed to the knowledge base with respect to MIC, there are still knowledge gaps and contradictions between studies.⁵⁶ This is largely due to the complexity of the deposits which form on the metal surface. These surface deposits include inorganic compounds from the environment and biofilms which accumulate on metals before pitting occurs.^7-9 In addition to its microbial communities, surface deposits on metals are composed of a heterogenous mixture of large organic molecules such as polysaccharides, proteins, lipids and nucleic acids, smaller inorganic species produced as intermediates and end-products of corrosion, metal deposits, and other metabolic products.^7,10 This results in chemical reactions which can impact the thermodynamics and kinetics of MIC development, thus making the process more difficult to understand.