Corrosion in multiphase slug flow loop in deep-water oil and gas exploitation

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Abstract:

The necessity to reduce cost in handling fluids requires a high flow rates with an inherent risk forturbulence influencing the corrosion process of the involved equipment. These conditions occur especiallyin offshore environments, as oil and gas production, and in chemical processes and energy productionindustries. There are several ways to discuss corrosion control associated to multiphase-flow- inducedcorrosion. One possibility is the mechanistic approach and the other makes use of professionals’ practicalexperiences. A pre-requisite for any effective control practices in multiphase flow induced corrosion is abasic understanding of the involved flow mechanisms. This work presents the study of the influence of slugmultiphase flow on API 5L X80 carbon steel pipe corrosion in an environment that simulates oil wells. Asa simulated environment, an 80 %water-cut mixture, comprised of 20 % light oil (10 cP) or heavy oil (150cP) plus 15 % of sodium chloride and 80 % of deionized water, was used. The tests were performed at 40oC under a different CO2 and H2S partial pressure balanced by N2 to reach a total pressure of 2.5 bar. Thetests were conducted in a multiphase simulating loop. All test parameters were monitored to guarantee aslug flow pattern. The conceptual design of the loop allowed the simultaneous evaluation of the influenceof the horizontal (0°) and inclined (45°) position of the flow to verify the influence of hydrodynamic effectson the weight loss. The conducted laboratory test results allow the establishment of empirical correlationsbetween the corrosion rate and specific exposure conditions. These correlations may be used in corrosionprediction softwares, which can help an engineer to design and to monitor life expectancies of industrialpipes. Studies conducted in autoclaves and in glass cells produce results which, despite here being usefulon the understanding of corrosion mechanisms, are not able to produce multiphase-flow regime resultslike those related to the conditions of pipelines in oil and gas exploitations. A smaller scale corrosion loopprovides a suitable environment for better reproducing hydrodynamic effects on the corrosion of pipe walls.In tests performed in the presence of only CO2, concavities on the carbon steel surface were observed. Thiswas attributed to the flow regime, which allowed the formation of a higher disperse-bubble volume andof an emulsion, either by the formation of an oil-in-water emulsion or a water-in-oil emulsion. However,the increase in CO2 partial pressure promoted, in all tested conditions, an increase of the weight loss rate. Thus, the work allowed scoring basic mechanisms of multiphase-flow-induced corrosion which intensifiesthe damages of carbon steel pipes in environments containing CO2 and H2S, in different concentrations andin controlled conditions of pressure and temperature.


Reference:
SILVA, Carlos Alberto da; NEVES FILHO; David Rodrigues da; NUNES, Gislaine Maria Bragagnolo; BASSANI, Gabriel Soares; ALMEIDA, Neusvaldo Lira; PANOSSIAN, Zehbour. Corrosion in multiphase slug flow loop in deep-water oil and gas exploitation. In: OFFSHORE TECHNOLOGY CONFERENCE BRASIL, Rio de Janeiro, 2019. Proceedings… 28 p.

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