An Experimental Investigation of Top-of-Line Corrosion in a Static CO₂ Environment

This paper presents an experimental and theoretical investigation into water condensation and corrosion under noncorrosion product forming conditions at the top of the line in a static, CO₂ environment. An experimental test cell is developed to measure droplet lifetimes, condensation rates, as well as in situ and integrated corrosion rates (using miniature electrodes and mass loss specimens, respectively) as a function of the surface and gas temperatures when the gas flow is dominated by natural convection. Experimental results show clearly that the water condensation rate is not very influential on the corrosion rate at low surface temperatures (T_s) (particularly below 25°C) but becomes much more important at higher surface temperatures (>40°C). These findings are summarized in a new empirical correlation for the top-of-line corrosion rate as a function of the condensation rate and surface temperature. A model for condensation at the top of line for static, buoyancy-driven conditions is also presented and is shown to predict dropwise condensation rates accurately for a range of experimental conditions. The developed miniature electrodes for in situ electrochemical measurement are shown to provide an accurate interpretation of the transient response in general corrosion behavior by giving real-time corrosion rates to complement the mass loss measurement.