Laboratory Simulation of Black Powder Formation in Flowing Gas with Water Condensation

Black powder formation in sales gas  pipelines was simulated using a gas flow loop with controlled water condensation. Separate sections with individual cooling systems allowed for simultaneous exposure with different condensation rates. The gas contained 1 bar CO₂ and various impurities of H₂S and oxygen.

Analysis of dissolved Fe²⁺ in the condensed water showed that the instantaneous corrosion rate was initially very high, and that it rapidly declined after a few days exposure due to build-up of partially protective surface layers. The corrosion rate increased with the condensation rate.

The composition of the corrosion products depended on the presence or absence of H₂S and O₂. The presence of traces of oxygen and H₂S can lead to formation of corrosion products consisting of a mixture of iron carbonate and iron sulphide. When oxygen is not present the corrosion products consist of iron sulphide. Iron oxide is found when H₂S is not present.