Corrosion Behavior of Oxide Scale of 5Cr Steel in CO₂ Flooding Environment

Abstract

Medium-Cr steel is considered as the most economical and effective pipeline material in a CO₂ flooding environment; however, the effects of iron oxides on the corrosion resistance of medium-Cr steel are still not clear. Therefore, in the present study, a high-temperature, high-pressure reactor was used to accelerate the corrosion of a rolled oxidized sheet of 5Cr steel. The corrosion behavior of oxide scale leaching was studied by comparing the mass loss and gain rate with bare steel, through using XRD, Raman, XPS, SEM, EDS, EPMA and other methods. It was found that the 5Cr steel rolled scale was composed of three layers: the innermost layer contained Fe₃O₄, the middle layer consisted of Fe₂O₃, and the outer layer contained Fe₃O₄ and a small amount of Fe₂O₃. In the CO₂ environment, the oxide scale mainly dissolved in the initial stage, and corrosion products were deposited in the later stage. The oxide scale delayed the occurrence of corrosion, and eventually, similar to the bare steel, a double-layer product film was formed. Also, the possible corrosion mechanism of the medium-Cr steel with the oxide scale was given.