Black Powder in Gas Pipelines - Sources

Sources

The source of black powder is far from clear, with several possibilities existing. Black powder could be generated from the following sources:

  • Mill scale (iron(II,III) oxide - Fe3O4) that comes from pipe manufacturing process through high temperature oxidation of steel. These types of solids are very persistent and strongly adhere to pipe wall and are not easily removed.
  • Flash rust (Fe2O33, FeOOH) from hydrotest water corrosion.
  • Internal pipelines corrosion (microbiological influenced corrosion (MIC) or H2S reaction with steel.
  • Carryover from gas gathering systems.

Black powder may be mechanically mixed or chemically combined with any number of contaminants such as water, liquid hydrocarbons, salts, chlorides, sand, or dirt. Chemical analyses of the material have revealed that it consists mainly of a mixture of iron oxides and iron sulfides.

Sour gas pipelines are always treated with corrosion inhibitors, while sweet gas pipelines are not. In both cases there is a chance of forming black powder at different rates. The rate of inhibition in sour gas lines is designed for normal operation, but there is always a chance of plant upsets that might introduce water to the pipelines. This water is not accounted for and will initiate the formation of black powder. Another source of solids formation in sour gas lines is the mechanical mixing of number of contaminants such as water, liquid hydrocarbons, salts, chlorides, sand, or dirt. If the lines are well inhibited, then the quantity of solids is not significant. Nevertheless, in sweet gas pipelines, which are not inhibited, any water condensation or any plant upset that could introduce water to the line will certainly lead to the formation of black powder.

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