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The crevice (grooving) corrosion of submarine pipelines for reservoir pressure maintenance system on the White Tiger oilfield

UDK: 622.692.1
DOI: 10.24887/0028-2448-2017-9-120-122
Key words: crevice (grooving) corrosion, water injection pipeline, sulfate-reducing bacteria, corrosion-mechanical damage
Authors: V.V. Savelev, A.N. Ivanov (Research and Engineering Institute, Vietsovpetro JV, the Socialist Republic of Vietnam, Vung Tau)

The work shows an especial case of streaming corrosion behavior of submarine pipeline systems on the White Tiger oilfield (offshore of Vietnam). Based on the results of visual inspection it was identified a presence of а «groove» with width up to 60 mm on the bottom of the pipeline. A reduction in the pipeline wall thickness at the 6 o’clock position was more than 85 %. The specific “tubercles” of the numerous sulfate-reducing bacteria colonies were also found on the inner surface of the pipeline, which would lead to the formation of the round-shaped defects (pits) in place, which sizes were 50-400 micrometers. The possible reason for increasing of micro-organism’s activity is possibly due to a periodical exploitation of the pipeline for reservoir pressure maintenance with a stoppage of prepared water pumping and finding dead lost-circulation zone. The presented results of composition analysis and the metal strength characteristics test within the defected zone of the pipe comply with the steel (X60 APIv5L). It was found that, the main components of the hard deposits on the inner surface of the pipeline were iron sulfates and sulfides content of which is more than 60 % by weight.

It was assumed, that the initial stage of further crevice corrosion development was a growth of sulfate-reducing bacteria colonies, which resulted in formation of loose layers of iron sulfates and sulfides sludges. If the sludges peeled off (because of them baseline adhesiveness to the metal surface), then in this case the sludges can become like an abrasive material. The sludges altogether with water flow remove the protective layer of inhibitor corrosion film and the metal oxides layer up the bare metal on the bottom of the pipeline. Then electro-chemical corrosion occurs in participation with coupled metals (galvanic pair) “metal (anode) – corrosion product (cathode)” and with a growth of corrosion up to 10-15 mm/year.

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