51312-01350-Evolution of corrosion scale of pipeline steel under high H2S/CO2 partial pressure

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Product Number: 51312-01350-SG

ISBN: 01350 2012 CP

Author: Lei Zhang

Publication Date: 2012

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Corrosion scale composed of iron-sulfur compounds can significantly affect corrosion process. However the transition of different crystals along with time under high H2S/CO2 partial pressure is not well understood. In this paper the H2S/CO2 corrosion of pipeline steel under 1.5MPa H2S and 0.2MPa CO2 partial pressures at 90oC was studied. SEM and XRD were employed to investigate characteristics and evolution of the corrosion products. Results indicated that the corrosion rate of pipeline steel decreased initially and then tended to steady. At the initial stage the corrosion products were constructed mainly by mackinawite (FeS1-x) crystals with a small amount of FeS crystals. Fe2+ diffused through the corrosion scale to its surface and then reacted with S2- and HS- nearby which resulted in growing up of mackinawite crystals gradually and thickening of the scale. Meanwhile a small amount of HS- and S2- diffused through corrosion scale to matrix/scale interface and reacted with Fe2+ which promoted the corrosion scale to grow inside as well. The content of Fe2+ at the scale surface was decreased due to incrassation of corrosion scale and thus the corrosion process was controlled by the growth of pyrrhotite (Fe1-xS) crystal. Since pyrrhotite crystals might nucleate and grow up just on the mackinawite crystals the surface of corrosion scale can be gradually vulcanized into pyrrhotite crystal layer. Key words: high H2S/CO2 partial pressure corrosion scale growth mechaniosm