With the increase in producing sour oil and gas fields in the world, mitigation of production related failures due to H2S corrosion is a key challenge. In H2S environments, localized corrosion is the type of attack which contributes to the most failures in oilfields. The main cause of localized attack is the galvanic coupling between steel and iron sulfide corrosion products due to their electrical conductivity. However, the mechanism of the galvanic coupling between steel and iron sulfides and the effect of experimental parameters on it, have not been unraveled yet. The present study investigates the effect of three different experimental parameters: iron sulfide type, cathode to anode surface ratio, and salt concentration, on the galvanic coupling between steel and iron sulfides in acidic solutions. Pyrite and pyrrhotite were selected as iron sulfide specimens since these corrosion products have been mostly found when localized corrosion of mild steel was observed in sour environments. The results show that the cathodic current of pyrrhotite was an order of magnitude higher than the cathodic current of pyrite, leading to a higher galvanic current as well as a higher galvanic potential for coupled steel-pyrrhotite compared to coupled steel-pyrite. In addition, it was found that the increase of cathode to anode surface area ratio as well as the increase of salt concentration to some extent, increased the galvanic current for the coupled materials.

Subject
Steel surfaces, Corrosion currents, Corrosion rate, Iron sulfides, Cathodic current, Galvanic cathodes, Anode surfaces, Pyrrhotite, Salt concentration, Pyrite, Galvanic coupling, Steel, Galvanic current
Keywords:
H2S Corrosion, Localized Attack, Galvanic Coupling, Iron Sulfides, Pyrite, Pyrrhotite, Mild Steel
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2022
Association for Materials Protection and Performance (AMPP)
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