This paper contains the results of a case history where oxygen contamination took place in a slightly
sour system. Details are also given on the laboratory testing results and development of corrosion
inhibitors for such an environment.
The ingress of oxygen had been occasionally detected in the slight sour water injection system via
storage tanks, the process system, pump seals and electrical cable to the aquifer wells. As a
consequence, severe localized corrosion (> 500 mpy) developed on the corrosion coupons when
oxygen intrusion was recorded during the exposure period. As a stronger oxidant than H2CO3, oxygen
greatly aggravates the corrosion attack by directly participating in the cathodic reaction, generally under
full or partial diffusion control. Oxygen intrusion can also create a more acidic local environment
through reaction with FeS solids generating elemental sulfur in the H2S containing system. However, to
the author’s knowledge, few publications have systematically addressed the effect of O2 in the inhibition
of carbon steel in the slightly sour system, particularly on the initiation and propagation of localized
attack.
In this paper, the effect of oxygen on the inhibition of slightly sour corrosion was studied by using
bubble testing cells with continuous H2S/CO2 mixture gas sparging and O2 intrusion. The corrosion
attack was quantified by and weight loss corrosion coupons and linear polarization resistance (LPR)
measurements.
Significant findings include the magnitude of localized attacks with and without the presence of
corrosion inhibitors.
Keywords: Oxygen corrosion, Iron sulfide, Waterflood, H2S, LPR, Slightly sour