Corrosion of low carbon steel by microorganisms from the ‘pigging’ operation debris in water injection pipelines

Present in all environments, microorganisms develop biofilms adjacent to the metallic structures creating corrosion conditions which may cause production failures that are of great economic impact to the industry. The most common practice in the oil and gas industry to annihilate these biofilms is the mechanical cleaning known as “pigging”. In the present work, microorganisms from the “pigging” operation debris are tested biologically and electrochemically to analyse their effect on the corrosion of carbon steel. Results in the presence of bacteria display the formation of black corrosion products allegedly FeS and a sudden increase (more than 400 mV) of the corrosion potential of electrode immersed in artificial seawater or in field water (produced water mixed with aquifer seawater). Impedance tests provided information about the mechanisms of the interface carbon steel/bacteria depending on the medium used: mass transfer limitation in artificial seawater was observed whereas that in field water was only charge transfer phenomenon. Denaturing Gradient Gel Electrophoresis (DGGE) results proved that bacterial diversity decreased when cultivating the debris in the media used and suggested that the bacteria involved in the whole set of results are mainly sulphate reducing bacteria (SRB) and some other bacteria that make part of the taxonomic order Clostridiales

Corrosion of carbon steel by bacteria from North Sea offshore seawater injection systems: Laboratory investigation

Influence of sulfidogenic bacteria, from a North Sea seawater injection system, on the corrosion of S235JR carbon steel was studied in a flow bioreactor; operating anaerobically for 100 days with either inoculated or filtrated seawater. Deposits formed on steel placed in reactors contained magnesium and calcium minerals plus iron sulfide. The dominant biofilm-forming organism was an anaerobic bacterium, genus Caminicella, known to produce hydrogen sulfide and carbon dioxide. Open Circuit Potentials (OCP) of steel in the reactors was, for nearly the entire test duration, in the range − 800 45), suggested pitting on steel samples within the inoculated environment. However, the actual degree of corrosion could neither be directly correlated with the electrochemical data and nor with the steel corrosion in the filtrated seawater environment. Further laboratory tests are thought to clarify the noticed apparent discrepancies