Abstract
Hydrogen sulfide (H2S) corrosion of mild steel is a serious concern in the oil and gas industry. However, H2S corrosion mechanisms, specifically at high partial pressures of H2S (pH2S), have not been extensively studied because of experimental difficulties and associated safety issues. The current study was conducted under well-controlled conditions at pH2S of 0.05 and 0.096 MPa. The pH range used was from pH 3.0 to pH 5.0, at temperatures of 30 and 80°C, and with rotating cylinder speeds of 100 rpm and 1000 rpm. Short-term exposures, lasting between 1.0 and 1.5 hours, were used to avoid formation of any protective iron sulfide layers. The experimental results were compared with a recent mechanistic model of sour corrosion developed by Zheng, et al. (2014). This model was based on corrosion experiments conducted at low pH2S (0.0001 – 10 kPa) and is applicable only to conditions where protective iron sulfide layers do not form. The validity of the model at higher pH2S was examined, as it was uncertain if the mechanisms identified at lower pH2S were still valid. The comparison with the experimental results obtained in the present study indicated a good agreement between the model and the measurements. This confirmed that the physico-chemical processes underlying H2S corrosion in the absence of protective iron sulfides are very similar across a wide range of H2S aqueous concentrations. It also demonstrated that the mechanistic corrosion model was reasonable when extrapolating from low to high pH2S.
