Electrochemical study and corrosion modeling of chromium alloy steels exposed to sulfide containing environment

Khaksar, Ladan (2018) Electrochemical study and corrosion modeling of chromium alloy steels exposed to sulfide containing environment. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Corrosion, the destructive result of a chemical reaction between a metal or metal alloy and its environment in sour systems (H₂S dominant) has progressively become a greater concern to the oil and gas industry as a result of production from increasingly sour environments. In this study, the effects of the principal H₂S corrosion product, iron sulfide, on the corrosion resistance of alloy steel were initially investigated, followed by the study of the corrosion behavior of alloy steels in the presence of elemental sulfur, which is often present in sour systems. A new experimental method was applied to synthesize the iron sulfide layer on the steel surface with no H₂S in the environment. Attempts were also made to develop an accurate computational model to predict the corrosion rate of alloy steel in various environmental conditions. A series of experiments was performed to study chloride concentration, temperature, immersion time and pH effects on the corrosion behavior of alloy steel in the simulated sour environment. Various analyzing methods, such as scanning electron microscopy and X-ray diffraction, were applied to investigate the results which suggest that each factor can significantly affect the electrochemical behavior of alloy steel, especially in the presence of H₂S corrosion products. The corrosion of alloy steel in the presence of elemental sulfur was also studied using the cyclic polarization technique. In general, it was shown that the presence of deposited layers of elemental sulfur on the surface of 13% Cr steel will increase the corrosion rate by decreasing the scaling tendency of corrosion products on the surface, especially at higher temperature. The experimental data were analyzed and used to develop an analytical model to show the effects of corrosion products, chloride concentration, pH and temperature on the likelihood of corrosion of 13% chromium steel.

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