Glass cell experiments were conducted to investigate kinetics of iron sulfide and mixed iron sulfide/carbonate scale precipitation in CO 2 /H 2 S corrosion. Weight gain/loss (WGL) method was used to investigate the scale formation using X65 carbon steel as substrates. Scanning Electron Microscopy (SEM/EDS), X-ray Diffraction methodology (XRD), X-ray Photoelectron Spectroscopy (XPS), and Electron Probe Micro-analyzer (EPMA) were used to analyse the scale. The experimental results show that the corrosion products formed in CO 2 /H 2 S system depend on the competitiveness of iron carbonate and mackinawite. At high H 2 S concentration and low Fe 2+ concentration, mackinawite was the predominant scale formed on the steel surface. At low H 2 S concentration and high Fe 2+ concentration, both iron carbonate and mackinawite form. It was also found that ferrous ions forming mackinawite scale mainly come from Fe 2+ released from the steel surface.
Keywords: kinetics, iron sulfide, iron carbonate, scale, precipitation, CO 2 /H 2 S corrosion