51315-5507-Construction and Verification of Pourbaix Diagrams for Hydrogen Sulfide Corrosion of Mild Steel

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Product Number: 51315-5507-SG

ISBN: 5507 2015 CP

Author: Jing Ning

Publication Date: 2015

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A comprehensive thermodynamic model has been developed for generating Pourbaix diagrams which can predict the formation of metastable and stable corrosion products in sour oil and gas environment (up to 250oC) including mackinawite (FeS) greigite (Fe3S4) pyrrhotite (Fe1-xS x=0 to 0.17) and pyrite (FeS2). The model is based on theoretical thermodynamic calculation and data collection from open literature. The Pourbaix diagrams were verified by multiple corrosion experiments in H2S environment. The principle of experimental validation is by comparing the proper predictions made by Pourbaix diagrams with iron sulfides formation in experiments and moreover by comparing the equilibrium line in Pourbaix diagram with the equilibrium state achieved in experiment. The features of Pourbaix diagrams are significantly affected by temperature since thermodynamic properties are sensitive to temperature. Accordingly Pourbaix diagrams were verified at different temperature (25oC 80oC). In addition Pourbaix diagrams were validated by changing solution pH and polarizing potential of the corroding carbon steel substrate in experiments. The experimental results generally agreed with the predictions made by the Pourbaix diagrams.