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.

Subject
Cathodic polarization, Water, Cylinders, Alkalinity, Salts, Corrosion rate, Alkaline solutions, Partial pressures, Liquids, Polarization curves, Carbon steel, Linear polarization resistance, Corrosion potential
Keywords:
Corrosion, anaerobic, glycol, low water concentration, alkalinity
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2021
Association for Materials Protection and Performance (AMPP)
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