Assessment of general and localized corrosion behavior of X65 and 13Cr steels in water-saturated supercritical CO2 environments with SO2/O2

Abstract

To mitigate the corrosive effect encountered in carbon steel pipelines during dense phase CO2 transport the general consensus is that the CO2 stream must be sufficiently dehydrated. Although such a process will undoubtedly help prevent the breakout of free water, it can contribute significantly towards the handling costs, particularly in the context of offshore installations. As opposed to drying the CO2 stream to excessive levels, one alternative option is the application of corrosion resistant alloys such as 13Cr. This paper performs a comparison between X65 carbon steel and 13Cr in pure and impure CO2, evaluating the influence of SO2 and O2 on the general and localized corrosion rate of both materials at 80bar and 35°C. The results show that 13Cr is able to perform exceptionally well in comparison to X65 in pure CO2 as well as when SO2 and O2 are present in the system individually, producing no localized corrosion and general corrosion rates below 0.02mm/y. However, when SO2 and O2 were combined, the formation of sulfuric acid was permitted which proved detrimental to 13Cr, producing excessive localized attack much greater than that observed on X65. Raman spectrosopy, XRD and SEM/EDX are used to analyse the corrosion products.