Internal corrosion of dry sales gas pipelines is normally overlooked due to the perceived
absence of condensed water. However, periodic cleaning of sales gas lines yield large
quantities of sludge that is composed of corrosion products known as black powder mixed with
other contaminants such as hydrocarbons (mainly TEG), elemental sulfur, sand, salts, water,
and metal debris. Two potential sources of water in the sludge are: (1) treated natural gas
whose water dew point exceeds the temperature of the pipeline, (2) water absorbed with TEG
carryovers or co-condenses with triethylene glycol (TEG) vapor.
In the present paper, the corrosion rate of carbon steel samples fully immersed in sales gas
pipelines black powder sludge containing high amounts of TEG was investigated after long
periods of exposure of 355days in oxygen-rich atmospheric environment and 100 days in
simulated sales gas compositions.
The steel samples immersed in the sales gas sludge showed no or extremely low corrosion
rates. In contrast, steel samples immersed in pure condensed deionized water showed
significantly higher corrosion rates of 1.0 mpy to 4.0 mpy. These results show that sales gas
black powder sludge has an inhibiting effect on the corrosion of these lines.
Keywords: black powder, sludge, TEG, corrosion, sales gas, pitting.