Localized Corrosion in an H2S/CO2 Environment

Large scale research is underway in an effort to understand the mechanisms that lead to localized corrosion in the presence of H₂S and CO₂.  An initial series of  flow loop experiments have been conducted over 30 day intervals at 60ºC, 7.7 bar partial pressure CO₂, pH 6.0,1 wt% NaCl, and partial pressures of H₂S from 0.1 mbar to 1.0 mbar with an additional experiment conducted at 1.0 mbar H₂S and 10 wt% NaCl.  This large-scale research was conducted in a 2000-liter system constructed with 10 cm I.D. pipelines of Hastelloy C-276.  Corrosion monitoring is conducted by weight loss (WL) coupons, with some electrochemical measurements of linear polarization resistance and electrochemical impedance spectroscopy.  Analysis by SEM is enhanced by the use of an Infinite Focus Microscope (IFM) to digitize the corrosion product film morphology and the features of the steel surface after corrosion product film removal.  Electron dispersion spectroscopy and x-ray diffraction are used for compositional analysis of the corrosion product film.  Localized corrosion was observed at 0.25 mbar H₂S and at 10 mbar H₂S where corrosion product films played a role in the process.