This study evaluates the susceptibility to localized corrosion of alloys UNS N06625 and N07725 in both supercritical and subcritical CO2 with H2S present. Electrochemical experiments were performed at 200°C, with CO2 present in both supercritical at 1500 psi and sub critical (450 psi) conditions, the H2S content was up to 10% mol and chloride concentration in the brine up to 25000 ppm, the test are performed with 1 g/l of S.

The results in this study, indicate that the performance of both alloys in supercritical CO2 phase with H2S, show an extremely high anodic dissolution rate. This behavior is attributed to the formation of NiCO3 and NiS. The H2S content within the supercritical CO2 phase can support a high cathodic reaction rate through the S reduction reaction, which is incorporated in the passive layer to form Ni sulfides, this creates a passive layer susceptible to pitting at high Cl- content.

Subject
Test methods, Cyclic polarization, Corrosion rate, Materials performance, Nickel based alloys, Autoclaves, Sodium chloride, Testing conditions, Brines, Pitting, Polarization, Alloys, Electrodes
Keywords:
Electrochemistry, corrosion resistant alloys, corrosion mechanisms, supercritical conditions
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2024
Association for Materials Protection and Performance (AMPP)
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