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51313-02785-Dense Phase CO2 Corrosion and the Impact of Depressurization and Accumulation of Impurities

Picture for Dense Phase CO2 Corrosion and the Impact of Depressurization and Accumulation of Impurities
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Product Number: 51313-02785-SG
ISBN: 02785 2013 CP
Author: Arne Dugstad
Publication Date: 2013
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When dense phase CO2 is depressurized and forms a two phase gas/liquid system impurities with lower solubility in the gas phase than in the liquid phase will accumulate in the liquid phase when the system is depressurized via the gas phase.

Partitioning and corrosion experiments were run at 4 and 25 °C in autoclaves that were loaded with dense phase CO2 and small amounts of water NO2 SO2 and H2S and then partly depressurized. The experiments showed that H2S SO2 NO2 and water accumulated while O2 was depleted in the remaining liquid phase. The carbon steel specimens that were exposed in the autoclaves corroded significantly after the system was partly depressurized. Lowest corrosion (< 0.1 mm/year) rates were measured in the system with CO2 and water (500-1200 ppmv) only. The corrosion rate is reasonably low because the water phase quickly becomes saturated with corrosion products that reduce the corrosivity. The situation was different when the CO2 contained SO2 (100-200 ppmv) and NO2 (100-200 ppmv) as these gases accumulate in the water phase reduce the pH and increase the reactivity of the aqueous phase. The specimens in the SO2 experiments got a black film and corrosion rates about 0.1 mm/year while the specimens in the NO2 experiment got a brown rusty layer of corrosion products and the corrosion rate was about 1 mm/year (500 ppmv water and 200 ppmv NO2). These high corrosion rates only last until the impurities are consumed and the replenishment of impurities becomes therefore an important issue for such experiments.

The paper describes the experimental approach and the obtained results and discusses the consequences of depressurization and accumulation of impurities with respect to corrosion and formation of solids in the pipeline.
 

When dense phase CO2 is depressurized and forms a two phase gas/liquid system impurities with lower solubility in the gas phase than in the liquid phase will accumulate in the liquid phase when the system is depressurized via the gas phase.

Partitioning and corrosion experiments were run at 4 and 25 °C in autoclaves that were loaded with dense phase CO2 and small amounts of water NO2 SO2 and H2S and then partly depressurized. The experiments showed that H2S SO2 NO2 and water accumulated while O2 was depleted in the remaining liquid phase. The carbon steel specimens that were exposed in the autoclaves corroded significantly after the system was partly depressurized. Lowest corrosion (< 0.1 mm/year) rates were measured in the system with CO2 and water (500-1200 ppmv) only. The corrosion rate is reasonably low because the water phase quickly becomes saturated with corrosion products that reduce the corrosivity. The situation was different when the CO2 contained SO2 (100-200 ppmv) and NO2 (100-200 ppmv) as these gases accumulate in the water phase reduce the pH and increase the reactivity of the aqueous phase. The specimens in the SO2 experiments got a black film and corrosion rates about 0.1 mm/year while the specimens in the NO2 experiment got a brown rusty layer of corrosion products and the corrosion rate was about 1 mm/year (500 ppmv water and 200 ppmv NO2). These high corrosion rates only last until the impurities are consumed and the replenishment of impurities becomes therefore an important issue for such experiments.

The paper describes the experimental approach and the obtained results and discusses the consequences of depressurization and accumulation of impurities with respect to corrosion and formation of solids in the pipeline.
 

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Results from novel transparent autoclave experiments. Carbon steel corrosion coupons were exposed to impurities levels within established specifications at simulated transport conditions (25 °C and 10 MPa of CO2).
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