Corrosion Inhibitor Development For Slightly Sour Environment With O2 Intrusion

This paper contains the results of the field observation when oxygen contamination took place in a slightly sour system, as well as the laboratory testing results on the development of corrosion inhibitors for such environment. The ingress of oxygen has been occasionally reported in the slight sour water injection system through the vapor space in the storages tanks, the pump seals, and electrical cable to the source water wells. As a consequence, severe localized corrosion (> 500 mpy) was developed on the corrosion coupons when oxygen intrusion was recorded during the exposure period. As a stronger oxidant than H2CO3 and proton, O2 would greatly aggravate the corrosion attack by directly participating in the cathodic reaction which is generally under full or partial diffusion control and create a more acidic local environment by reacting with FeS solids to generate 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, particular on the initiation and propagation of localized attack. In this paper, the effect of oxygen on the inhibition of slight sour corrosion was studied by using bubble testing cells with continuous H₂S/CO₂ mixture gas sparging and occasional O₂ intrusion of a period of 2-4 hours in the total 7-day long test. The corrosion attack was quantified by linear polarization resistance (LPR) measurements and weight loss corrosion coupons. Significant findings include the magnitude of localized attacks at different O2 concentrations and intrusion periods without and with the presence of corrosion inhibitors.