Black Powder Formation in Thin Water Layers Under Stagnant Conditions

Black powder formation was simulated using carbon steel samples with a thin water layer. Temperature, alkalinity, TEG content and the partial pressures of O₂, CO₂ and H₂S were systematically varied in glass cell experiments to study the effect on corrosion rate and corrosion products formed.

The corrosion rate was almost unaffected by variation in CO₂, H₂S and O₂ partial pressure. The corrosion rate was significantly reduced in high TEG solution. Compared to distilled water, addition of alkalinity had just minor effect on the corrosion rate, except for CO₂-free conditions.

Two essentially different regimes of corrosion products were identified. Magnetite formation dominated in CO₂-free conditions while siderite and goethite formed in the presence of CO₂.