Effect of Triethylene Glycol on Corrosion of Carbon Steel in H2S, CO2, and O2 Environments

Internal corrosion of dry sales gas pipelines is often overlooked due to the perceived absence of condensed water.  However, periodic cleaning of sales gas lines often yields large quantities of material known as black powder, which can only be attributed to internal corrosion. Two potential sources of condensed water are: (1) treated natural gas whose water dew point exceeds the temperature of the pipeline, (2) water that co-condenses with triethylene glycol (TEG).
This paper describes a research study that was conducted to provide estimates for corrosion rates of carbon steel in TEG-water mixtures with TEG content in the range 0.0wt% to 99.5wt%. Fifteen-day tests in stagnant thin layer TEG-water mixtures were performed to study the effects of hydrogen sulfide, carbon dioxide, and oxygen gases on corrosion rates.
The results showed that the corrosion rates in pure distilled water (0.0wt%TEG) were low, ranging from 0.96 to 4mpy. For all investigated gas compositions, these low initial corrosion rates rapidly dropped even lower with increasing TEG content in the TEG-water mixtures.  At a TEG content of 90wt% and greater, the corrosion rates become virtually 0.0mpy regardless of the gas composition.