Failures of main oil pipelines are often caused by the development of internal corrosion. Although commercial oil that is pumped through the main oil pipelines meets Russian National Standard, during its transportation in low and stagnant zones of the pipeline, produced water containing various mineral impurities and in-pipe sediments is released and accumulated. As a result of these processes, the corrosion activity of pumped medium increases in places where produced water and bottom sediments accumulate, it increases even more sharply when they are microbiologically contaminated; at the same time, the number of defects due to internal corrosion increases constantly. The greatest danger is the contamination of produced water and in-pipe sediments with sulfate-reducing bacteria (SRB). The article presents the results of laboratory studies of changes in the corrosion activity of a model medium from a stagnant zone, which is a mixture of commercial sour oil, produced water and in-pipe sediments, when diluted with a fresh portion of commercial oil. The titer of SRB in the mixture was 105 CFU/ml. The test results showed that when a fresh portion of commercial oil is added to the stagnant zone where corrosion products containing adherent microorganisms have formed on the metal surface, the corrosion rate decreases and there is a low effect of protection against general corrosion (up to 54,5% when the mixture is diluted with commercial oil in the ratio of 1:1). When the medium is completely replaced with a fresh portion of oil, the corrosion rate over the next 7 days increases to values exceeding the reference corrosion rate, which indicates the restoration of the vital activity of microorganisms and, as a result, an increase in the corrosion rate. Thus flushing of stagnant, dead-end and non-flowing zones with pumped oil does not ensure the termination of corrosion processes under sediments and is not effective without cleaning bottom sediments from the pipeline surface and combating bio contamination of metal surface by an adherent population of microorganisms. Laboratory tests of water-dispersible inhibitor A, widely used to protect oil field pipelines in hydrogen sulfide-containing environments, have shown its low efficiency (about 50 %) in a biologically contaminated environment, since it does not suppress the vital activity of microorganisms, although to some extent protects the metal from the products of their vital activity. A study of the effectiveness of using bactericide B showed that complete suppression of adherent sulfate-reducing bacteria occurs at a minimum effective dosage of bactericide of 500 g/m3. Based on the data obtained, it can be concluded that this bactericide can be used for periodic treatment of oil field media with a dosage of 500 g/m3. To achieve a long-term protective effect from flushing of stagnant zones with commercial oil, it is necessary to combine it with cleaning of sediments and using chemical reagents with protective and bactericidal properties.
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