Black powder formation in sales gas pipelines was simulated using a gas flow loop with controlled water condensation. Separate sections with individual cooling allowed for simultaneous exposure with different condensation rates. The gas was water saturated at 26 °C and contained CO2 and impurity levels of H2S and O2.

The mass loss corrosion rate was in most cases close to 0.1 mm/y and unaffected by the gas compositions tested here. 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 of exposure due to build-up of partially protective surface layers.

The composition of the corrosion products (black powder) changed considerably with small changes in gas content. A mixture of siderite, iron sulfides, iron oxides and elemental sulfur formed in the presence of CO2 (1 bar), H2S (0.1 mbar) and O2 (12 mbar). Siderite and iron oxides formed in the presence of CO2 and O2, while only iron sulfides formed in CO2 and H2S.

Subject
Water, Iron oxide, Corrosion rate, Iron sulfides, Pipelines, Condensation rates, Corrosion loops, Siderite, Black powder, Corrosion products, Corrosion attacks, Gas composition, Elemental sulfur
Keywords:
Black powder, Corrosion, Loop test, Carbon steel
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2011
Association for Materials Protection and Performance (AMPP)
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