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Corrosion behavior of pipeline steel transporting diluted bitumen

University of British Columbia

An insufficient understanding of the corrosion, especially the internal corrosion, of diluted bitumen (referred to as “dilbit”) pipelines exacerbates the debate around new pipeline construction. This thesis elucidates the effects of important parameters, such as the presence of bitumen, chloride droplets, steel deformation, and the size of silica particle deposits, on the internal corrosion of pipeline steel. The inclusions and matrix of API-X100 pipeline steel before and after 30 days of exposure to bitumen were characterized by ex-situ scanning electron microscopy and the results showed that no obvious corrosion can be observed to occur at the inclusions or the matrix at 60 and 120°C. In order to understand their role in pipeline corrosion, chloride droplets on API-X100 pipeline steel were covered by a non-corrosive oil (paraffin oil), and used to simulate the corrosive environment encountered in dilbit pipelines. The corrosion under a paraffin-covered chloride droplet is distinct from the traditional Evans droplet in that the active corrosion is governed by the initial stochastic nature of pit density rather than differential aeration of oxygen. Further, bitumen was diluted with paraffin oil to simulate dilbit with a 30:70 paraffin oil to bitumen volume ratio. The areas covered by simulated dilbit did not show any corrosion, confirming the non-corrosive nature of simulated dilbit. The chloride droplet corrosion penetration into pre-deformed API-X100 pipeline steel and ASTM A106B pipeline steel beneath simulated dilbit was 1.17 ± 0.06 and 1.18 ± 0.09 times higher than that for the same steels without pre-deformation, respectively. The corrosion behavior of API-X100 pipeline steel under large (80% cumulative distribution = 540 µm) and small (80% cumulative distribution = 43 µm) silica particles and submerged beneath chloride droplets covered by simulated dilbit was also studied. The maximum penetration rate of localized corrosion under the larger-sized silica particles was 1.4 ± 0.1 times that of the localized corrosion beneath the smaller-sized silica particles. Chloride droplets originating from upstream processing are a threat to the integrity of dilbit pipelines. This threat increases if the steel is deformed and if internal deposits, which often carry the water, consist of larger particles.

Text

2020-03-26

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/73808

Materials Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/