Corrosion Of Mild Steel In Concentrated Monoethylene Glycol (MEG)

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The thermodynamic hydrate inhibitor MEG is a robust choice for long distance gas-condensate tie-backs operating at low temperature. The possibility to regenerate and recycle the MEG enables cost effective operation with low discharges. The choice of regeneration process depends on the salt content of the produced water.

Product Number: 51321-16701-SG

Author: Marion Seiersten

Publication Date: 2021

Member Price: $20.00

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Material selection for Monoethylene glycol (MEG) regeneration units is a challenge due to the high temperature combined with high salt content. The oxygen level is low, and carbon steel is a cost-effective choice. The corrosion rate of carbon steel is too high in neutral or acidic conditions, but in alkaline solution, C-steel might be an alternative even without the use of film forming corrosion inhibitor.
The corrosion rate of carbon steel in ca. 97 wt% MEG at 120 C, is quite low in alkaline solutions. If the MEG solution contains more than 2 mmol/kg alkalinity, the corrosion rate is in the range 0.1 mm/y to 0.3 mm/y when the CO2 partial pressure is 300 Pa or less. The low corrosion rate is not due to passivity. In alkaline solutions with more than 97 wt% MEG, some test coupons showed a passive behaviour from start of experiments, but they became activated after cathodic polarisation and did not re-passivate in 4 weeks.
At 120 C the cathodic reaction is activation controlled in solutions with more than 97 wt% MEG and alkalinity above 20 mmol/kg. The reaction rate is independent of shear stress and has a low alkalinity dependence. It is probably governed by the reduction of water.