Corrosion of Carbon Steel during High Temperature Regeneration of Monoethylene Glycol in the Presence of Methyldiethanolamine

The use of methyldiethanolamine (MDEA) as a pH stabilizer in natural gas pipelines utilizing monoethylene glycol (MEG) injection is an attractive option in systems with high carbon dioxide (CO2) partial pressures. However, the presence of MDEA within MEG loops may pose a corrosion risk to carbon steel systems operating at high temperatures including the primary MEG regeneration unit due to the effect of temperature on MDEA dissociation behavior. Carbon steel corrosion rates were measured within CO2-free lean glycol solutions containing 500 mM MDEA from pH25 °C = 6–11 at 30, 80, 140, and 180 °C. Heating of the lean MEG solution, analogous to the regeneration process, facilitated corrosion through the deprotonation of MDEA’s conjugate acid, MDEAH+, leading to an increase in hydrogen ions available for cathodic reduction. The effect of temperature on MDEA dissociation behavior led to carbon steel corrosion rates in excess of 1 mm/year for systems operating below pH25°C = 9 and ≥ 140 °C.