Thermodynamic Analysis of the Formation of Black Powder in Sales Gas Pipelines

The product of reaction between steel pipelines and the 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 pipelines.  The difficulty in understanding the mechanisms for formation of this material comes 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 what is commonly known in the gas industry as black powder.  Given the complex nature of the formation of black powder in natural gas pipelines, 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 pipelines environment.  The software used for the calculations was the Facility for the Analysis of Computational Thermodynamics (FACT-SAGE). 
Our findings showed that thermodynamics can be a useful tool to predict what can, and cannot, possibly form under dew conditions. Due to these uncertainties, the results should be used as a guide to better understand the corrosion mechanisms inside the pipeline.