Evaluating the Efficacy of H2S/CO2 Ratio in Predicting Corrosion Mechanisms in Amine Treating Units

Abstract The molar or partial pressure ratio of H2S to CO2 (H2S/CO2) has traditionally been considered a straightforward parameter for determining the dominant corrosion mechanisms, particularly in pipeline transportation and downhole operations. This ratio has guided designers and operators in installing and operating necessary corrosion mitigation strategies. While the H2S/CO2 ratio is a valuable concept in pipeline and downhole operations, its application in amine treating units is more complex. In these systems, the free H2S and CO2 content depends on the saturation level of the amine with these gases. Therefore, relying solely on this ratio to predict corrosion behavior in amine treating processes is insufficient. When water is present, understanding the free H2S and CO2 available to dissolve in the water can provide additional insights. Other environmental and process conditions such as temperature, pressure, water content, fluid compositions, and thermodynamic free energy also play critical roles. This paper examines a case where an increased H2S/CO2 ratio was expected to reduce corrosion in amine strippers. However, over-stripping of the amine and oxygen ingress led to continued corrosion challenges. This case highlights the limitations of relying solely on the H2S/CO2 ratio. The paper discusses optimal operational practices and adequate corrosion control measures to mitigate associated risks. The insights and conclusions provide a clear path forward for addressing corrosion challenges in similar amine systems, fostering safer and more efficient operations in the industry.