Long-Term Corrosion Behavior of Cr Alloyed Steels in Aqueous CO2 Environments Containing Chlorides

Abstract This study evaluated the long-term corrosion behavior of 1Cr and 3Cr steels in aqueous environment containing carbon dioxide and chlorides. Tests lasting from 25 to 61 days were conducted using a 5 L glass cell with multiple steel samples, uniform hydrodynamic conditions, and controlled water chemistry. All tests were performed at 80°C, CO2 partial pressure of 0.52 bar and moderate wall shear stress (~2 Pa). Both 1Cr and 3Cr steels exhibited comparable corrosion rates from 3 to 1 mm/y for up to about 25 days of exposure. However, between 25 to 35 days of exposure, a sharp decrease in corrosion rate and an abrupt increase in open circuit potential was measured for 3Cr steel samples indicating the occurrence of a pseudo passivation process. On the other hand, 1Cr steel maintained high corrosion rates between 1 and 1.5 mm/y while exposed for up to 61 days. The better long-term performance of 3Cr steel would be related to the formation of a pseudo passive protective film consisting of chromium oxy-hydroxide and spinel oxide, favored by its larger chromium content and the more uniform and compact precursor chromium hydroxide layer formed on this material.