Understanding Naphthenic Acid Corrosion in Refinery Settings

Naphthenic acid corrosion has plagued refineries for nearly a century. However, the vast majority of naphthenic acid corrosion research to date is solely focused on remediation, and not understanding the fundamental mechanism of corrosion. To further the current state of understanding in order to mitigate corrosion, experiments were performed to address the corrosion mechanism of iron, as well as of the ferrous alloying elements. In addition, electrochemical methods were used to determine the presence of acids within nonpolar solvents, such as a crude. The structure of the acids in solution was studied with FT-IR and Raman spectroscopy to understand how the acids self-associate as a function of temperature, concentration and presence of a metal. The results have yielded that iron corrodes via an etch pitting mechanism. In addition, this work has determined that the mechanism of resistance of chromium and molybdenum are their passive films, and that these metals are susceptible to naphthenic acid attack if the passive films break down. The mechanism of resistance of these elements provides insight into the failure mode of 304 and the 400 series stainless steels in naphthenic acid service. A particular result of interest is that nickel catalytically decomposes naphthenic acids at high temperatures (e.g. 270°C) via a catalytic mechanism. Finally, a palladium hydride reference electrode was developed that functions in aprotic solvents, and an ionic liquid was synthesized that allowed for the electrochemical detection of naphthenic acids in toluene