Temperature Sensitivity of the Corrosion Performance of 316L in Concentrated Sweet Brines

There is little data available in the public domain on the performance of UNS S31603 (316L) in concentrated anoxic brines saturated with CO₂ in the absence of H₂S. A series of pitting corrosion and electrochemical tests were performed, aimed at assessing the suitability of 316L in an anoxic brine where the chloride concentration was up to 250 000 mg l^-1. The electrochemical test results obtained found that pitting potentials and re-passivation potentials were lowest at 65 °C. At lower and higher temperatures (25 °C and 112 °C) the pitting and re-passivation potentials were nobler than the corresponding values at 65 °C. It is postulated that the increased risk of corrosion at 65 °C is due to the competing effects of increasing pH and decreasing CO₂ solubility vs. increasing temperature. The pitting test results allow some of the performance boundaries for 316L in anoxic CO₂ saturated brines to be tentatively defined. However, whilst the polarization tests performed demonstrate that that the highest exposure temperature is not necessarily the point at which the risk of passive film breakdown is highest (in contradiction to normal expectations) there was not a reliable correlation between E_pit and the presence or absence of corrosion in autoclave tests.