Alternating Current (AC) interference affects pipelines collocated near high voltage transmission lines. While overhead high voltage AC transmission line collocations are common underground high voltage AC transmission line collocations while less common can cause similar interference effects on pipelines. This paper describes a feasibility evaluation of a proposedunderground transmission line route in the United Kingdom affecting a nearby pipeline. The proposed transmission line was to consist of either three 220 kV circuits or six 132 kV circuits; both cases were evaluated. The proposed transmission line phase cables were to be installed with concentric sheath conductors direct buried in a close trefoil configuration and bonded to underground splice boxes at various locations. In addition to the proposed transmission line route the project evaluated a set of base cases: a typical pipeline paralleling at varying offsets for various lengths under a variety of operating conditions and a typical pipeline crossing scenario. The effect of soil resistivity on the interference levels experienced by the pipeline was considered. The feasibility study assessed the expected steady state fault state and AC corrosion effects that the proposed transmission line could have on any nearby pipelines. Results for all cases and scenarios will be discussed.Key words: AC interference case study underground AC power transmission pipeline integrity
Microbiologically influenced corrosion (MIC) is a persistent problem for many oil and gas production operations. Carbon steel pipelines are particularly susceptible to biofilm formation by microorganisms which consequently threatens the integrity of these lines. Although MIC within pipelines is challenging to mitigate it is generally accepted that pigging a mechanical cleaning process that removes water oil scales and solids from the pipeline surface is an effective method to control biofilm formation. However not all pipelines can be effectively pigged to counter biofilm development. In many cases partially removed or unremoved biofilms are 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 has 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. Biofilms were grown for a period of 3 weeks in order to establish base (unmitigated) MIC rates. 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 a CI-containing medium or (3) a combination of both. Biofilms were incubated for an additional 6 weeks following these treatments to allow for biofilm regrowth. The impact of these treatments on the resulting MIC rates was evaluated by comparing the weight loss corrosion rates and localized pitting corrosion of the carbon steel coupons. Additionally qPCR and 16S rRNA gene sequencing were used to enumerate and identify the different corrosive microbial communities that developed on the coupons following the different treatments. Fundamentally different effects of corrosion inhibitors on MIC were observed depending on whether these chemicals were applied to a pre-formed biofilm or to mechanically cleaned steel surfaces.