Formation of Iron Sulfides at Elevated Temperature (80-160 °C) and Their Effect on Corrosion of Mild Steel

Abstract Both H2S and CO2, ubiquitous in hydrocarbon production and processing, have the potential to severely compromise asset integrity. While both are corrosive, H2S containing environments can be particularly aggressive, causing more rapid and severe corrosion compared to CO2; especially in high temperature oil and gas production systems. There has been limited investigation of H2S corrosion at elevated temperatures, resulting in a deficient understanding of the underlying mechanisms responsible for observed phenomena. Consequently, corrosion research related to the presence of H2S gas is of particular interest to the oil and gas industry. The key goal of the experimental work herein was to compare observed phenomena for high temperature H2S corrosion against results from previous investigations, with a deepened data analysis. Data for autoclave experiments conducted at pHinitial 4.0, 0.00385M [H2S]aq (1.6-2.0% H2S) contrasting corrosion product layers at 80 and 160 °C are reported. Experimental results using two API 5L X65 mild steels demonstrate that corrosion rates at 80 and 160 °C were essentially the same, within measurement error, with mackinawite found at 80 °C and a combination of iron sulfides (pyrrhotite, mackinawite) with magnetite found at 160 °C. However, localized corrosion appeared on the X65 specimens at 160 °C.