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.
Key words: Black powder, Corrosion, Loop test, Carbon steel