Corrosion inhibition of carbon steel in aqueous CO(sub 2) solutions

摘要

The thesis concerns the corrosion inhibition of carbon steel in offshore oil and gas production systems. In oil and gas production systems carbon steel has been widely employed as construction material both in process facilities and transmission pipelines. When carbon dioxide is present in these systems, it dissolves in the aqueous phase forming carbonic acid. In this thesis efforts have been made to obtain information that can contribute to increase the relevance of laboratory test methods by investigations of the corrosion and corrosion inhibition of carbon steel in aqueous CO(sub 2) solution. Experiments have been performed at 35, 50, 65 and 80(sup o)C with both stationary disc electrodes and rotating cylinder electrodes. The inhibitor performances of an amine and phosphate ester corrosion inhibitor have been investigated with emphasis on the fact that metal surfaces are more or less corroded before inhibitor is introduced. In addition, the action of the inhibitors has been studied under flowing conditions. An adsorption model has been used to analyse the adsorption process of the phosphate ester inhibitor at 35(sup o)C. The results indicate occurrence of two processes related to the adsorption of the inhibitor. The first process describes the initial adsorption where the adsorption rate appears to be dependent on the inhibitor concentration. A follow second process where the adsorption rate is found to be independent of the concentration, may indicate a growth or reorganization of the inhibitor on the surface. It is found that the interface inhibition mechanism may be used to describe the interaction between the inhibitor and the metal surface at 35(sup o)C. The investigations in this thesis have shown that laboratory testing of corrosion inhibitors has to be matched against field conditions to improve their relevance and increase the fundamental understanding of inhibitor action in real systems. 125 refs., 155 figs., 13 tabs.