The product of reactions between steel pipelines and some species in processed natural
gas is a significant concern to the gas industry. The corrosion product, which is a mix of iron
oxides, sulphides, and carbonates, has several impacts on pipeline operations and must be
periodically removed by pigging the pipeline. The difficulty in understanding the mechanisms
of formation of this material comes in large part from the non-uniform conditions, such as water
dew point, H2S, CO2 and O2 concentrations, in the pipeline.
This paper provides an evaluation of the application of chemical thermodynamics to the
formation of this material - what is commonly known in the gas industry as black powder.
Given the complex nature of the formation of black powder, it was decided to study the
formation and stabilities of various iron phases, namely iron oxides, sulfides and carbonates as
well as elemental sulfur in sales gas pipeline environments.
Our findings show that thermodynamics can be a useful tool to indicate what can, and cannot,
possibly form under dewing conditions; however, compositional analysis of the powder can
assist in directing the calculations. Due to these uncertainties, the results should be used as a
guide to better understand the corrosion mechanisms inside the pipeline.
Keywords: black powder, computational thermodynamics, internal corrosion, Sales Gas,