| Top of the line corrosion (TLC) is a significant concern in wet gas transportation, where temperature gradients between internal pipeline and outside environments lead to the condensation of water vapor and a certain fraction of hydrocarbons. Liquid water from condensation is greatly corrosive as it is saturated with acidic gases; e.g., CO2, H2S and CH3CO2H. TLC is specific to a stratified flow regime when the upper portion of the pipe is not in contact with the flowing liquid phase. Therefore, a conventional mitigation technique such as corrosion inhibitor injection is not successful because the delivery of the corrosion inhibitor is governed by the flow regime. Extensive research has been conducted to better understand this phenomenon and develop improved corrosion mitigation techniques.;Up until the commencement of this project, only hydrocarbon-free TLC systems had been studied. In reality, a certain fraction of hydrocarbons will condense along with water and form two immiscible liquids with different wettability and different corrosivity. This study investigates the influences of straight chain hydrocarbon condensation on TLC. The study is divided into three parts: (i) experimental investigation of wettability and co-condensation processes, (ii) experimental study of corrosion in a co-condensation environment, and (iii) the prediction of water condensation rate in multi-component systems.;The co-condensation process was monitored using various techniques, which were as visual observation and electrochemical method. Results showed that water has the stronger affinity towards the carbon steel surface. Water accumulates on the steel surface and occupies the majority of the surface regardless of test conditions.;During corrosion tests, iron carbonate (FeCO3) grows on the steel in co-condensation environments but does not do so during water condensation under the same testing conditions. Surface characterization showed that smaller water droplets are found in co-condensation, indicating that the water is segregated. The water chemistry analysis showed that this can lead to a rise in the pH within the aqueous phase, and hence to less corrosion. Improving the prediction of water condensation rate, which is the primary parameter in determining the severity of TLC, directly helps to assess the TLC severity. Most of the available TLC prediction models assume that the only condensing component is water. In fact, the presence of condensing hydrocarbons affects the heat and mass transfer within the system. A multi-component co-condensation rate prediction model is developed here and validated with experimental data. The results show that the water condensation rate slightly decreases when hydrocarbons are considered. This is because less heat is given away due to condensation of water alone as condensing hydrocarbons contribute a portion of the heat flux. Furthermore, other physical and hydrodynamic properties change in favor of lowering water condensation rate. Yet, the effect is small because the latent heat of vaporization of water is significantly higher than that of hydrocarbons.;Additionally, a thermodynamic diagram of water and hydrocarbon is created and coupled with the temperature and pressure profile of the pipe to aid in the determination of locations that are liable to suffer from TLC. |
