Determination of Oxygen Limits for Corrosion Resistant Alloys (CRAs) in Oil & Gas Produced Water Based on Electrochemical Test Methods – Part 2

Small amount of oxygen in production or injection systems can be responsible for the initiation of crevice corrosion of stainless steel. The current limit of 10 ppb dissolved oxygen (DO) recommended for the use of Corrosion Resistant Alloys (CRAs) in produced water system, has been challenged by several authors. The aim of this study is to report the use of electrochemical methods for the study of oxygen limits for stainless steels UNS⁽¹⁾ S31603 (Type 316L) and UNS S31803 (Type 22Cr Duplex) in produced water environments. Crevice corrosion potential (Ecrev) and repassivation potential (Erep) were obtained from cyclic polarization experiments performed in part 1 of this study. These two potentials were used as acceptance criteria during open circuit potential (OCP) measurements to determine the oxygen limits of Type 316L and Type 22Cr Duplex at given test conditions. The effect of the duration of exposure to oxygen as well as the effect of increase of oxygen content were discussed. Results obtained for Type 316L indicate that the current oxygen limit of 10 ppb is relevant for long-term and permanent exposure. A precise determination of oxygen limits for Type 22Cr Duplex could not be performed due to uncertainties related to the variations of Ecrev and Erep at low oxygen concentrations. A re-assessment of oxygen limits based on the data obtained in this study is planned based on revised acceptance criteria. Key words: Crevice corrosion, produced water, Corrosion Resistant Alloys, oxygen, electrochemistry.