The role of Cl- in the formation of the corrosion products and localised corrosion of 15Cr martensite stainless steel under an CO2-containing extreme oilfield condition

This paper focused on the corrosion behaviour of 15Cr stainless steel in deep/ultra-deep geological environments. The relationship between corrosion products and general/localised corrosion under various Cl- concentrations at 200 °C and 28.5 bar pCO2 were systematically investigated. The results indicate that high Cl- content of 81 000 ppm promoted the general/localised corrosion via precipitation of the chloride-rich products, which retarded the formation of nanocrystalline NiFe2O4 and decreased the corrosion resistance. The corrosion products consisted of outer FeCO3 and inner NiFe2O4/FeCr2O4/Cr(OH)3 in a low Cl- content of 29 503 ppm. The characterisation of the corrosion products is combined with thermodynamics calculations.