Study of the Localized Nature of Top of the Line Corrosion in Sweet Environment

The phenomena of interest in this study are related to the transportation of gas containing condensable liquids and, more precisely, the corrosion issues that occur when significant heat exchange is present between the pipelines and the surroundings. The unprocessed vapor mixture flowing through the pipe has the potential to condense particular components on the cold walls, one of them being water, forming a thin film and/or droplets of corrosive liquid. In this work, the occurrence of localized corrosion in top of the line corrosion (TLC) was investigated in a sweet (CO₂-dominated) environment, with a focus on understanding the influence of the environmental parameters on localized TLC in order to develop a narrative for the mechanism. A unique setup was developed for the experimental work involving the use of carbon steel inserts exposed to three different levels of cooling at the same time. This concept was quite successful in simulating realistic localized features. A series of long term exposure (1- to 3-month) experiments was conducted to investigate the controlling parameters. The occurrence of localized corrosion could be very clearly correlated to the condensation rate, the gas temperature, and the organic acid content. Additional statistical information related to the morphology of localized TLC features could be collected, providing useful insight on the mechanisms involved. Finally, the very peculiar morphology of typical localized TLC features and the interaction between condensation pattern and corrosion attack were also characterized. However, no clear relationship could be established with certainty between the presence of droplets and the extent of the corrosion attack. Instead, the water condensation rate (WCR) was thought to control the corrosion and the overall aggressiveness of the environment.