Internal corrosion and anticorrosion protection of offshore facilities in the presence of increased amounts of carbon dioxide

• R.K. Vagapov, R.R. Kantyukov and D.N. Zapevalov

Gazprom VNIIGAZ LLC, 15 Proyektiruyemy proyezd 5537, bld. 1, Razvilka, Leninsky municip., Moscow region, 142717, Russian Federation

Abstract: Some operating and promising offshore hydrocarbon production facilities are characterized by an increased content of corrosive CO₂ in the extracted products. The paper investigates the dynamic nature of the medium flow in the pipeline system at offshore facilities. To determine this factor, which has an intensifying effect on the internal corrosion processes, the shear stress was calculated taking into account the main operational parameters of such offshore fields. The authors compare several models for calculating the rate of internal corrosion with regard to the offshore gas field conditions. An empirically derived formula to assess the temperature and salinity impact on the corrosion rate resulting data is estimated. The paper analyzes comparability of the calculated results for different dependencies with the own corrosion rate data obtained during the gravimetric tests for the operating conditions of the offshore fields. Corrosion under moisture condensation conditions, which occurs at a temperature gradient and rapid cooling of the produced gas is most aggressive and dangerous. Tests show that the rate of local carbon dioxide corrosion can reach several mm/year. The authors estimate the severity of the influence of monoethylene glycol concentration used as a hydrate inhibitor in a water–glycol medium and its contribution into the corrosion rate, both in a liquid medium and during moisture condensation in the vapor phase. The presence of glycol can reduce corrosion in a liquid medium, but during moisture condensation, corrosion suppression is not influenced by the concentration of glycol in the evaporated liquid, but by its content in the liquid condensed on the steel surface.

Keywords: carbon dioxide corrosion, offshore object facility, corrosion rate, inhibitory protection, local corrosion

Int. J. Corros. Scale Inhib., 2021, 10, no. 3, 1128-1140
doi: 10.17675/2305-6894-2021-10-3-17

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