Failure of 24" Common Crude Piping and Formation of Iron Sulfides Due to the Influence of Sulfate & Iron Reducing Bacteria and Methanogens

A leak suddenly occurred at the 24-inch common crude piping from the separators heading to the degassing boot inlets and the wet crude tanks at an oil gathering center in Kuwait Oil Company. The initial observations showed the leak was due to a deep isolated pit and localized corrosion. Consequently, the piping spool was opened, deposits were collected for analysis and an action report was issued recommending replacing the leaky spool. Additional inspection by manual and long range ultrasonic thickness measurements for the 24" common crude line showed similar deep isolated pits (up to 70% thickness reduction) scattered across the length of the 1100 meter piping. This was extremely concerning since the facility has just been commissioned and been in service for 1.5 - 2 years only. Subsequently, an investigation was carried to determine the root causes for the failure concluded that an active Microbiologically Influenced Corrosion (MIC) possibly was taking place due to the influence of sulfate & iron reducing bacteria and methanogens. These different bacteria types formed biofilms at different pockets leading to deep isolated pitting, and the formation of iron sulfide layer found adhered at the 6 o'clock position along the length of the piping. The iron sulfide layer observed was confirmed to be present due to the activities of sulfate reducing bacteria and influenced by iron reducing bacteria and methanogens, since H₂S was found in the crude stream at extremely low content in gas (1 ppm). Additionally, other factors such as flow velocity have contributed to the MIC and pitting / localized corrosion as it was found to be below 1 m/s, which promoted stagnation and stagnant conditions in the process stream. Further, calcium carbonates (CaCO₃) played a major part in the observed damages, since it was formed non-uniformly across the length of the piping, promoting exposed pockets for biofilm formation, tubercles and under deposit corrosion. The results of this interesting investigation is presented in this paper.