The present study has been conducted to investigate the electrochemistry of mild steel corrosion in mixed H2S/CO2 aqueous environments and develop an electrochemical model to simulate the experimental results. The experiments were designed to determine the effect of H2S on CO2 corrosion for short term exposures of a few hours before any interference from iron sulfide corrosion product layers happened. Tests were conducted at different H2S concentrations ranging from 0 to 10% in the gas phase at 0.1 MPa total pressure at pH4 and pH5 respectively. Corrosion rates were measured by linear polarization resistance (LPR) and the corrosion mechanisms were investigated by using potentiodynamic sweeps. Results showed that the presence of H2S slowed down the charge transfer kinetics related to H2CO3 reduction and H2O reduction on the metal surface. An electrochemical model was developed for a mixed H2S/CO2 system which was calibrated with new experimental results and compared to data found in the open literature. The model predictions fit experimental data well for short exposures (measured in hours) but overestimate the experimental results for longer term exposures (measured by days and weeks) due to the formation of an iron sulfide corrosion product layer, which is not accounted for in the present model.

Subject
Hydrogen concentration, Corrosion rate, Electrochemical models, Predicted corrosion rate, Sodium chloride, Gas pressure, Mixtures, Partial pressures, Sodium chloride solution, Experimental data, Corrosion modeling, Steel, Risk reduction
Keywords:
hydrogen sulfide, carbon dioxide, electrochemistry, model
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2014
Association for Materials Protection and Performance (AMPP)
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