The impact of minor Cr additions in low alloy steel on corrosion behavior in simulated well environment

Low alloy steel samples with different Cr content (0‒3 wt%) have been exposed to simulated well environment. It is revealed that the 3%Cr sample initially has the highest corrosion resistance. However, due to faster formation of a Fe x Ca y CO 3 protective scale in the 0%Cr sample, this sample demonstrates the highest corrosion resistance after 2 days of exposure. While the Fe x Ca y CO 3 scale is also formed in the 1%Cr sample, the scale is weakly adhered and porous, which does not enable good corrosion resistance. Although the scale formation is delayed in a sample with 3 wt%Cr, once it is formed, the presence of Cr-rich phase in this scale provides greater long-term corrosion protection. Localized corrosion attack is observed in the samples with 0% Cr and 1%Cr, whereas the 3%Cr sample shows no sign of localized attack due to initial pre-passivation and the ability to rebuild the protective scale.