The nature of the iron sulfide films formed on steel surfaces during H2S/CO2 corrosion is
a key parameter for pH stabilisation in sour gas pipelines, and will also affect the efficiency of
corrosion inhibitors. On this background, a series of systematic experimental studies of iron
sulfide corrosion film growth in aqueous H2S/CO2 environments have been initiated. This
contribution presents results obtained in the initial stages of these studies using gravimetric
(mass loss) methods, FE-SEM and EDS.
X65 carbon steel samples were exposed to sour conditions for various periods of time up
to 10 days. Evidence of iron sulfide layer formation governed by the parabolic film growth rate
law was found for the test conditions reported, indicating that the corrosion and film growth
rates in these cases were limited by the electronic conductivity of the film or mass transport,
probably Fe2+ diffusion, across the corrosion film. Assessment of the films by SEM revealed
that the morphology changes with exposure time within the range studied.
Keywords: sour corrosion, FeS film growth, FeS film morphology, localized corrosion