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Based on two hypotheses of the cause of this type of localized corrosion: an electrochemical galvanic effect and a chemical effect. Observations indicate that the electrochemical galvanic hypothesis was the key mechanism in this type of localized corrosion.
In the previous study by the same authors, a localized corrosion mechanism related to the presence of pyrite corrosion product was proposed by observing and replicating severe localized corrosion in sour environments. In the present study, in order to further validate this localized corrosion mechanism, a comprehensive mechanistic study of localized corrosion was designed and conducted. The experimental design was based on two hypotheses addressing the cause of this type of localized corrosion: an electrochemical galvanic effect and a chemical effect. Thus, novel experiments involving deposition of pyrite particles onto the bare steel surface and onto steel covered by a thin electrically insulating mesh surface were conducted in an aqueous H2S solution. It was found that no localized corrosion was observed when the physical contact between pyrite particles and the steel underneath was eliminated by using an insulating mesh. Moreover, the experiments were also performed in aqueous CO2 solution for further validation. Based on the experimental observations, the electrochemical galvanic hypothesis was proven to be the key mechanism in this type of localized corrosion.
Keywords: Hydrogen sulfide, corrosion, localized corrosion, pyrite, galvanic effect
Quantitative analysis of the corrosion morphology after accelerated testing and outdoor exposures of lapjoint test panels coupled with various fastener materials. Image analysis of 3-D microscope images was used to quantify average depth of attack and percent surface area damage.
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The formation of greigite and/or pyrite seems to correlate with onset of localized corrosion Experiments involving deposition of pyrite on the steel surface were conducted to investigate if localized corrosion occurs when pyrite is deposited on mild steel in an aqueous H2S environment.
Black tar-like fouling material was driving frequent shut-downs of a gas plant. Analysis indicated that the nitrogen containing corrosion inhibitor (CI) polymerized with sulfur compounds in a vulcanization process. Testing confirmed the role of the CI in creating this fouling.