Mitigation of top‐ and bottom‐of‐the‐line CO₂ corrosion in the presence of acetic acid (II): Inhibition using azole derivatives

Abstract

Carbon steel flowlines transporting hydrocarbon fluids are susceptible to internal corrosion in the aqueous phase at the base (6 o'clock position) and in aqueous condensed droplets at the top (12 o'clock position). Respectively, these issues are known as “bottom‐of‐the‐line” corrosion and “top‐of‐the‐line” corrosion and inhibitors that are used to control internal pipeline corrosion need to be effective at both locations. Here, we explore whether 2‐mercaptobenzimidazole (2‐MBI), 2‐phenyl‐2‐imidazoline (2‐PI), 2‐amino‐5‐ethyl‐1,3,4‐thiodiazole (2‐AETD), are able to control CO2 corrosion simultaneously at both the top‐ and the bottom‐of‐the‐line in the presence and absence of acetic acid, a common minor constituent of produced hydrocarbon fluids. The performance of the species varied between highly effective (2‐MBI), moderately effective (2‐AETD) to ineffective (2‐PI). Inhibition was effective at both bottom‐ and top‐of‐the‐line, and with acetic acid present. Given that the vapor pressure of these species is negligible, it is suggested that they are carried from the bulk phase to the top‐of‐the‐line dissolved in aerosol droplets rather than in the vapor phase.