The corrosion of carbon steel in the presence of Monoethylene Glycol (MEG) - Assessing the influence of an iron carbonate scale

Carbon steel pipelines are employed in the transportation of wet natural gas from source to process plant. Corrosion and formation of hydrates is an important threat to the integrity of the pipeline if not properly controlled. In order to protect pipelines from hydrate formation, Monoethylene glycol (MEG) is often used. The continuous use of pH stabilizers in natural gas pipelines can lead to the formation of desirable and undesirable scale formation. If the use of pH stabilizers gives negative effects due to the formation of unwanted scale, the increase in the pH of the system is no longer effective and corrosion rates may increase. Alternatively measures may be introduced to maintain the integrity of pipelines such as the use of corrosion inhibitor. This paper investigates conditions where there is a significant formation of corrosion scale in the form of iron carbonate in wet gas systems. The continuous use of high pH at certain points of the pipeline is reconsidered with a focus on the formation of scale. The effect that lowering the pH of the solution has on the corrosion rate and existing protective corrosion product is evaluated. Synergistic and antagonistic effects of MEG with iron carbonate scale are determined with particular considerations of the use of alternative corrosion protective methods at reduced pH.