Current Understanding of Corrosion Mechanisms Due to H2S in Production Environments

In has long been recognized that the mechanism of corrosion in sour systems is more complicated than the simple release of ferrous ions into solution followed by the precipitation of the iron sulfide species appropriate to the environmental conditions.  Research conducted to date has identified the most common species of iron sulfides that form under oil and gas production conditions and the corrosive environments that is normally required to produce each.  It now appears that in many cases, a multi-step process is involved between the formation of the initial iron sulfide tarnish film and the final corrosion product scale.  A summary is presented of what is known about this multistage process, how it relates to different temperature and H₂S partial pressure conditions and what still remains to be determined.