Kinetics of Iron Sulfide and Mixed Iron Sulfide/carbonate Scale Precipitation in Co2/h2s Corrosion

Glass cell experiments were conducted to investigate kinetics of iron sulfide and mixed iron sulfide/carbonate scale precipitation in CO2/H2S 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 CO2/H2S system depend on the competitiveness of iron carbonate and mackinawite. At high H2S concentration and low Fe concentration, mackinawite was the predominant scale formed on the steel surface. At low H2S concentration and high Fe concentration, both iron carbonate and mackinawite form. It was also found that ferrous ions forming mackinawite scale mainly come from Fe released from the steel surface.