Effect of Cr/Mo on the protectiveness of corrosion scales on carbon steel in sweet medium under high flow regime

Abstract

We investigate the effects of Cr/Mo micro-alloying of plain carbon steel on the corrosion behaviour and scale protectiveness in CO2 saturated (sweet) brine (0.5 M NaCl) environment, under hydrodynamic conditions, at 80oC in a slightly acidic environment (pH 6.6). Potentiostatic current transients indicate positive effects of Cr/Mo micro-alloying on an individual as well as synergistic level of the alloyents. Increase in Cr/Mo content appears to reduce the overall current passing through corrosion scale and encourage faster crystallization. SEM images suggest that Cr/Mo micro-alloying induced formation of thinner scale with better protectiveness. From the mechanistic perspective, we suggest that the addition of small amounts of Cr/Mo modulates the current due to dissolution of iron, as well as the current due to growth of a crystalline layer, by modifying the local environment at the steel surface. Modeling of the hypothesis is currently in progress.