During the past decade, a number of research facilities have conducted investigations of H2S
corrosion under conditions that have produced mackinawite as the corrosion product. Field
experience with oilfield equipment has frequently found the corrosion product to be pyrrhotite
under conditions that appear similar to these laboratory studies. A review of publications that
were able to produce pyrrhotite revealed that pH, temperature and the length of exposure all
appear to play a role in the development of the FeS corrosion product. In longer term
exposures, there also appears to be a multi-stage film growth mechanism where mackinawite
forms first and then ruptures. Following film rupture, a second stage of FeS film growth occurs
and it is during this second phase where several forms of FeS can form, depending upon pH,
temperature and mass transfer characteristics of the system.
H2S, Pyrrhotite, Troilite, Cubic FeS