Top of line corrosion (TLC) was studied in a flow loop under conditions representative for a gas field with a low CO2 partial pressure of 0.35 bar and presence of acetic acid in the gas. The temperature in the experiments was 60 and 90 °C, and Mono Ethylene Glycol (MEG) was present in the bulk aqueous phase. The water condensation rates used in the experiments were calculated from multiphase flow simulations for the planned pipelines. The experimental results showed that the condensed water contained both MEG and acetic acid.
With this low CO2 partial pressure, the organic acids gave a significant contribution to the overall TLC rate. At 80 – 90 °C and high acetic acid, the TLC rates were 0.13 mm/y. When the organic acid content was reduced by 90 % the TLC rates were reduced with approximately 50 %. At 60 °C the condensation rates were lower but the iron solubility higher, and the TLC rate was 0.11 mm/y.
Investigation of exposed corrosion coupons showed that a partly protective film of iron carbonate corrosion products had formed on the surface. The surface film reduced the TLC rate but did not provide full protection. The TLC rates measured in the experiments were lower than modelled TLC rates for cases with high organic acid content, showing that the TLC model was on the conservative side for such cases.
This paper presents TLC work that was carried out in connection with a gas field with a low CO2 partial pressure of 0.35 bar and presence of organic acid. It is planned to use mono ethylene glycol (MEG) to prevent hydrate formation. Organic acids may accumulate in the MEG cycle, and this effect was included when the experimental content of organic acids was selected.