Key parameters affecting sweet and sour corrosion: Impact on corrosion risk assessment and inhibition

In the oil and gas industry, transport fluids contain a significant amount of dissolved CO2 and H2S, contributing to roughly 60% of internal corrosion failures. These failures lead to the loss of millions of dollars in inspection, maintenance, and replacement of metallic structures. The severity, rate, and mechanism of corrosion in CO2 and H2S-rich environments depend upon numerous parameters such as temperature, CO2 and H2S partial pressures (PCO2 and PH2S), pH, flow velocity, salt concentrations and availability of chemicals species such as corrosive gases, organic acids, and amines. The impact of these parameters is complex and can affect sweet and sour corrosion in diverse ways. Generally, the increase in temperature, PCO2 and PH2S, and pH favors the formation of corrosion products on the metal surface thereby reducing the corrosion rate. On the other hand, the increase in the flow velocity and the presence of organic acids create the opposite effect. The formation of corrosion products depends upon the PCO2 and PH2S as in CO2, H2S and their mixed regimes. FeCO3, FeS and a mixture of FeCO3 and FeS form major corrosion products, respectively. The present review outlined the important key parameters affecting sour and sweet corrosion. In addition, the impact of the parameters on corrosion risk assessment and inhibition was discussed. Also, existing knowledge gaps and future research directions were proposed. The main findings of this review are that the key parameters affecting sweet and sour corrosion are temperature, pH, partial pressures of CO2 and H2S, flow rate, concentration of organic acids and salt concentrations (brine). However, the effect of these parameters on sour corrosion is less investigated compared to sweet corrosion.