Glass cell experiments were conducted to investigate kinetics of iron sulfi de and mixed iron sulfi de/carbonate layer formation in carbon dioxide/hydrogen sulfi de (CO 2 /H 2 S) corrosion of mild steel using the weight change method. Scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), x-ray diffraction methodology (XRD), and x-ray photoelectron spectroscopy (XPS) were used to analyze the layer. The experimental results show that mackinawite is the predominant type of iron sulfi de layer formed in short exposures in pure H 2 S solutions. The type of layer formed in a CO 2 /H 2 S solution depends on the competitive mechanism of iron carbonate and mackinawite formation. At high H 2 S concentration and low dissolved iron carbonate supersaturations, mackinawite was the predominant component in the layer; at low H 2 S concentration and iron carbonate supersaturations, both iron carbonate and mackinawite may form on the steel surface. It was also found that the corrosion rate of mild steel in H 2 S corrosion is affected by H 2 S concentration, temperature, velocity, and the protectiveness of the layer.
Under certain conditions, hydrocarbons may alter the internal corrosion conditions of oil and gas pipelines. In this paper, the effects of hydrocarbons on corrosion have been predicted based on the type of emulsion (i.e., water-in-oil or oil-in-water), wettability (oil-wet, water-wet, or mixed-wet), and corrosiveness of brine in the presence of hydrocarbons. Laboratory methodologies have been developed to determine wettability and to identify the type of emulsion under pipeline operating conditions. Using these methodologies, the wettability and the type of emulsion have been determined for 14 hydrocarbons obtained from operating pipelines. The corrosiveness of brine in the presence of hydrocarbons also has been determined using rotating cage experiments.
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