Corrosion processes and mechanisms in the presence of MonoEthylene Glycol (MEG)

Carbon steel pipelines are employed in the oil and gas industry for long distance multiphase transportation. The integrity of these pipelines is critical to oil and gas production. Transportation of wet natural gas using carbon steel pipelines from source to processing plant may lead to corrosion, hydrate formation and even scale formation. To prevent hydrate formation MonoEthylene Glycol (MEG) is pumped through the pipeline. Corrosion inhibitors and other corrosion prevention methods may be employed to reduce corrosion to manageable and acceptable levels.
In this study the corrosion inhibition properties of MEG were investigated at both low and high temperature conditions. The reduction of carbon steel X65 corrosion in the presence of MEG alone and 1% NaCl alone at low temperature of 20°C was in line with previous studies. At high temperature of 80°C, the corrosion rate of the carbon steel in the presence of MEG tends to increase. Thus the reduction of the corrosion rate of carbon steel in the presence of MEG can be underestimated.
The increase in the corrosion rate of carbon steel in the presence of MEG at high temperature led to the search for the mechanism by which MEG reduces corrosion. The adsorption process was studied using Fourier transform infra-red spectroscopy (FTIR). Further determination of the adsorption isotherm properties and behaviour of MEG on the corrosion of carbon steel was recorded through experimentation. The results were used to determine the type of adsorption that occurs in the presence of MEG.
The corrosion rate of carbon steel in the presence of MEG is improved by deployment of chemical inhibitors to reach a minimal acceptable rate. This study investigated the use of two types of commercially-available inhibitors green (inhibitor 2) and non-green inhibitor (inhibitor 1) for reduction of the corrosion rate. The effects of the two inhibitors alone on the corrosion of carbon steel at both high and low temperatures were first examined. This enabled an assessment of the inhibitor in the presence of MEG.
A combination of the MEG and inhibitor was tested at both low and high concentrations. The influence on MEG on the inhibitor performance was determined.
Conditions necessary for the formation of protective iron carbonate were determined and used for pre-corrosion. The influence of iron carbonate on the corrosion of carbon steel was determined.
Pre-corroded carbon steel was used to assess the influence of MEG in the presence of iron carbonate. Further test on the pre-corroded carbon steel in the presence of MEG and inhibitor was performed to assess the influence of the inhibitor and MEG on iron carbonate scale.