Adsorption of Oil onto API-X100 Pipeline Steel in CO 2 -Saturated Solutions
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TRODUCTION
CO2 corrosion in oil and gas pipelines depends on the types of the transported multiphase flows.[1] Constituted primarily of hydrocarbon oil, stratum water, and entrapped CO2 and H2S gases, a number of flow regimes can develop depending on the amounts and velocities of the constituent phases, and on a number of intertwined physicochemical factors.[2,3] The impacts of specific flow regimes on the corrosion behavior have been investigated in previous studies in flow loops in which the amounts and velocities of the phases were varied and controlled.[4–6] The findings—from a fundamental viewpoint, regardless of a regime type, demonstrate the fact that the corrosion rates increasingly become higher and difficult to control when the amounts of water are more than those of oil. Transporting pipeline flows from newly explored reservoirs does not conventionally pose a considerable potential of corrosion damage[7] since oil, which is the abundant constituent to transport, acts as a natural barrier to cover the pipeline surfaces and inhibit the corrosion reactions. The situation, however, becomes critical as an oil reservoir ages to have less oil to need, as a result, an enhanced recovery by pressurized fluids. With time, water constitutes the majority of the transported flow within which CO2 has a greater capacity to dissociate. The concentrations of the corrosive carboncarrying species, as a result, increase, and the pH decreases in the water phase to whom increasing surface areas are exposed.
FAYSAL FAYEZ ELIYAN, Research Assistant and AKRAM ALFANTAZI, Professor, are with the Corrosion Group, Department of Materials Engineering, The University of British Columbia, Vancouver, BC, V6T 1Z4, Canada. Contact e-mail: [email protected] Manuscript submitted March 12, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
The emphasis in this article is to examine, on an electrochemical basis, some basic thermodynamic aspects that might govern the adsorption of oil in association to its concentration and temperature. We had previously reported that oil suppressed the corrosion rates of the API-X100 steel in 1-bar CO2-saturated solutions[8–10] and bicarbonate solutions,[11] without suggesting a mechanism or elucidating thermodynamic reasons. In this research, oil adsorption is postulated to be ascribed to an active aromatic constituent, tetrahydronaphthalene (C10H12), in a test hydrocarbon fuel, which was reported by Ayello et al.[12] as one of the likeliest polar compounds to adsorb onto the corroding surfaces and inhibit the reactions. We introduced, in 1-bar CO2-saturated solutions, low 10, 20, and 30 vol pct oil concentrations of which the concentrations of C10H12 were calculated for which Langmuir adsorption isotherms were postulated valid to construct. This article is one of the first recent efforts devoted to understand the thermodynamic interrelations of oilbased inhibition with CO2 corrosion when investigated by electrochemical methods. Suppression of corrosion rates by oil was mostly evaluated by weight-loss measurement
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