The effect of temperature on carbon steel corrosion under geological conditions

We investigated the role of temperature on the carbon steel corrosion under simulated geological conditions. To simulate the effect of temperature increase due to radioactive decay, we conducted batch experiments using Callovo-Oxfordian (COx) claystone and synthetic water formation with steel coupons at 30 °C and 90 °C for 6 months. The corrosion products have been studied by scanning electron microscope/energy dispersive X-ray spectroscopy, X-ray diffraction and micro-Raman spectroscopy. At 30 °C, experiments showed the formation of magnetite and iron sulphide, indicating the activation of sulphate-reducing bacteria. At 90 °C a continuous iron sulphide layer was identified on steel surface due to the reduction by hydrogen of pyrite originating from claystone into pyrrhotite and hydrogen sulphide. Thus, sulphide production may occur even in the absence of microbial activity at high temperature and must be taken into consideration regarding the near-field geochemical evolution.