Journal
CORROSION
Volume 71, Issue 8, Pages 945-960Publisher
NATL ASSOC CORROSION ENG
DOI: 10.5006/1566
Keywords
hydrogen sulfide; H2S corrosion; iron sulfide; polymorphous; Pourbaix diagram; thermodynamic
Funding
- Anadarko
- Baker Hughes
- BP
- Chevron
- Clariant Oil Services
- CNPC Tubular Goods
- ConocoPhillips
- DNV GL
- Hess
- INPEX Corporation
- M-I SWACO
- Multi-Chem
- Nalco Champion
- Occidental Oil Company
- Petrobras
- Petroleum Development Oman
- Petroleum Institute (GRC)
- Petronas
- PTT
- Saudi Aramco
- Sinopec
- TransCanada
- TOTAL
- Wood Group Integrity Management
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In the present study, a comprehensive thermodynamic model, depicted by Pourbaix diagrams, was developed with the relatively narrow focus on corrosion of mild steel in oil and gas field conditions. This thermodynamic model focuses on predicting the formation of metastable or stable corrosion products in sour environments at elevated temperature up to 250 degrees C, which includes mackinawite (FeS), greigite (Fe3S4), the pyrrhotite group (Fe1-xS, x = 0 to 0.17), and pyrite (FeS2). The model is based on theoretical thermodynamic calculations and data found in the open literature. The appearance of Pourbaix diagram is significantly affected by temperature. Long-term corrosion experiments at two different temperature (25 degrees C and 80 degrees C) were conducted to investigate the corrosion product stability predictions made by the Pourbaix diagrams. The equilibrium state predicted in the Pourbaix diagrams was compared with the quasi-equilibrium state attained in the long-term experiments. To this end, the surface pH, bulk pH, ferrous ion concentration in solution, and corrosion potential were all monitored throughout the experiments. The morphology and composition of corrosion products formed on the mild steel sample surface was analyzed using scanning electron microscopy and x-ray diffraction. It was observed that the experimental results generally agreed with the predictions made by the Pourbaix diagrams.
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