Comparison of 3%-Cr steel and carbon steel corrosion behavior as well tubing materials in CO₂–H₂S environment

This study provides two case studies involving carbon steel and 3%-Cr steel exposed to a CO₂–H₂S environment with a moderate scaling index. The carbon steel tubing show shows pitting and severe corrosion, whereas the 3% chromium steel tubes are undamaged. XRD results showed that the chromium-rich layer did not alter scaling on both tubes. Investigations using SEM and EDS reveal the formation of a dense and compact layer in the 3%-Cr steel, which serves to resist corrosion. In contrast, carbon steel has a porous structure and is easily detachable due to wall shear stress caused by slug movement. In 3%-Cr steel, the EDS analysis reveals a compact layer with a significant number of chromium, which is an indication of a Cr-rich iron oxide layer. Potentiodynamic polarization shows that the anodic curve is shifting, which means that the rate of corrosion is slowing down. This study shows that 3% Cr steel is a good choice for a mixed CO₂–H₂S environment with a high total dissolved solid (TDS).