Observations on the effect of simulated pigging and corrosion inhibitor exposure on microbiologically influenced corrosion of carbon steel

Although microbiologically influenced corrosion (MIC) in pipelines is challenging to mitigate, it is generally accepted that pigging, a mechanical cleaning process that removes water, scales and other solids from the pipeline surface, is an effective method to control biofilm formation. However, not all pipelines can be pigged and as such biofilm development may occur undisturbed from mechanical impacts. Regardless of the absence or presence of a mechanical cleaning program, oilfield biofilms are often exposed to continuously injected, film-forming corrosion inhibitors (CI) which are used to mitigate acid gas corrosion in pipelines. To date, the individual and combined effects of pigging and CI injection on biofilm formation and subsequent corrosion have not been well-studied. To this end, corrosive consortia consisting of sulfate-reducing bacteria and methanogenic archaea were grown as biofilms on carbon steel coupons under defined laboratory conditions. Once biofilms were established, the coupons were exposed to one of the following corrosion mitigation treatments: (1) simulated pigging using a wire brush, (2) exposure to CI at a concentration of 50 ppm, or (3) a combination of both treatments. Fundamentally different effects of CI on MIC were observed depending on whether these chemicals were applied to pre-formed biofilms or to previously mechanically cleaned steel surfaces.