Kinetics of Corrosion Layer Formation. Part 2—Iron Sulfide and Mixed Iron Sulfide/Carbonate Layers in Carbon Dioxide/Hydrogen Sulfide Corrosion Available to Purchase

Glass cell experiments were conducted to investigate kinetics of iron sulfide and mixed iron sulfide/carbonate layer formation in carbon dioxide/hydrogen sulfide (CO₂/H₂S) corrosion of mild steel using the weight change method. Scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), x-ray diffraction methodology (XRD), and x-ray photoelectron spectroscopy (XPS) were used to analyze the layer. The experimental results show that mackinawite is the predominant type of iron sulfide layer formed in short exposures in pure H₂S solutions. The type of layer formed in a CO₂/H₂S solution depends on the competitive mechanism of iron carbonate and mackinawite formation. At high H₂S concentration and low dissolved iron carbonate supersaturations, mackinawite was the predominant component in the layer; at low H₂S concentration and iron carbonate supersaturations, both iron carbonate and mackinawite may form on the steel surface. It was also found that the corrosion rate of mild steel in H₂S corrosion is affected by H₂S concentration, temperature, velocity, and the protectiveness of the layer.