Microbially Influenced Corrosion
An asset Integrity challenge that requires a collaborative effort.
The Challenge
 Microbially influenced corrosion (MIC) is caused when microorganisms produce chemicals that change the local environment to a more corrosive state. Over the past 30 years, case histories of MIC have been reported by many industries, including the chemical, paper, power, marine and petroleum industry. By some estimates, MIC has been involved in as many as 10 percent to 30 percent of all serious corrosion cases and has been implicated in corrosion of most commonly used metals, including corrosion resistant alloys. Biofilms are communities of micro-organisms adhering to the metal surface and encased in a polymeric network synthesized by members of the community. They form when free-swimming bacteria become attached to the surface of the pipe where they then colonize and mature.
In seawater and oilfield produced waters, sulfate-reducing bacteria (SRB) are often members of these biofilm communities and will produce sulfides through the oxidation of naturally occurring soluble organics indigenous to the formation brines. Sulfides (HS-, H2S) will precipitate with ferrous iron at the anode forming iron sulfides and acid. Others claim it is the formation of iron sulfide deposits by the SRB that forms a large cathode enabling the rapid reduction of protons to hydrogen. However, all seem to agree that biofilms are important since they enable a stabilized flow of current between the anode and the cathode, which is only transitory in the absence of biofilm. If this is sustained, localized coupling between the anode and cathode results in eventual pit propagation and growth leading to leaks.
 The Answer?
Several theories have been proposed to explain the aggressive pitting associated with MIC based on biofilms and biological products (e.g., acids and cathodic minerals). Until an understanding of the fundamental mechanisms allows the industry to build accurate predictive models, MICs must be managed through intelligent design, prevention and monitoring regimes. Corrosion engineers and scientists are developing models to better explain localized corrosion due to CO2, H2S and acetate, and the more complex nature of MIC. It will require a long-term commitment on the part of a multidisciplinary team of scientists and engineers to tackle this challenge. ConocoPhillips hopes to meet this challenge through its continued support of the localized corrosion modeling efforts at the Ohio University Institute for Corrosion and Multiphase Technology and a new Joint Industry Project being launched at the University of Calgary on microbial corrosion.
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