2006 F.N. Speller Award lecture: Development of corrosion-resistance alloys for the oil and gas industry - Based on spontaneous passivity mechanism

Corrosion-resistant alloys (CRA) have been developed to withstand severe corrosive production environments that the oil and gas industry has been facing in the last few decades. CRA alloy design has been carried out based on spontaneous passivity mechanism in carbon dioxide (CO2) and/or hydrogen sulfide (H2S) containing environments. The spontaneous passivity characteristics were studied taking into account both the analysis of corrosion products formed in CO2 and/or H2S environments as well as the calculated solubility of ferrous carbonate (FeCO3), oxides and sulfides. FeCO3 formation is strongly related to severe localized corrosion of carbon steels in CO2 environments. Cr oxide corrosion products in Cr steels act as the spontaneous passivity film to prevent corrosion in CO2 environments. The corrosion products consisting of Mo and Ni sulfides on the outer layer and Cr oxide on the inner layer act as the spontaneous passivity film in H2S environments. It was found that Mo is a particular effective element in repairing the passive film at localized corrosion initiation locations, because the lower the pH, the lower the solubility of Mo oxide and sulfide at elevated temperatures.