The number of sour oil and gas fields worldwide is increasing, as sweet fields are being
depleted and high oil prices vouch for profitable development of sour oil and gas finds. Sour oil and gas
production and transport always imply a risk of material damage and shutdowns due to CO2/H2S
corrosion, and especially localised corrosion attacks. The mechanisms behind localised CO2/H2S
corrosion are not fully explained, with unanswered questions regarding the effect of FeS corrosion film
breakdown, contribution of galvanic effects from electronically conductive FeS films to the pit growth,
and the effect of steel microstructure on localised corrosion. This paper provides a discussion on the
mechanisms of different types of localized H2S/CO2 corrosion attacks, based on observations from
laboratory experiments and from the field.