Effect of Sales Gas Pipelines Black Powder Sludge on the Corrosion of Carbon Steel

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), sand, salts, elemental sulfur, water and etc.  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 that becomes by TEG carryovers or co-condenses with triethylene glycol (TEG) vapor.

In this paper, the corrosion rate of carbon steel samples fully immersed in sales gas pipelines black powder sludge with high amounts of TEG and exposed, for long periods of time of 90day to 355days, to an atmosphere of simulated sales gas composition was investigated using weight loss method.  

The steel samples immersed in the sales gas sludge showed no or extremely low corrosion rates. In contrast, steel samples immersed in pure condensed distilled water showed significantly higher corrosion rates of 1.0 mpy to 2.0 mpy.  These results show that sales gas sludge has an inhibiting effect on the corrosion of these lines.