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Effect of main controlling factor on the corrosion behaviour of API X65 pipeline steel in the CO2/oil/water environment

Yuanpeng Cheng (Department of Oil and Gas Storage and Transportation Engineering, Yangtze University, Wuhan, China, Department of Oil and Gas Storage and Transportation Engineering, China University of Petroleum Huadong, Qingdao, China and Provincial Key Laboratory of Petroleum Storage and Transportation Security, Qingdao, China)
Zili Li (Department of Oil and Gas Storage and Transportation Engineering, China University of Petroleum Huadong, Qingdao, China)
Yalei Zhao (Department of Oil and Gas Storage and Transportation Engineering, China University of Petroleum Huadong, Qingdao, China)
Yazhou Xu (Department of Oil and Gas Storage and Transportation Engineering, China University of Petroleum Huadong, Qingdao, China)
Qianqian Liu (Department of Oil and Gas Storage and Transportation Engineering, China University of Petroleum Huadong, Qingdao, China)
Yu Bai (Department of Oil and Gas Storage and Transportation Engineering, Yangtze University, Wuhan, China)

Anti-Corrosion Methods and Materials

ISSN: 0003-5599

Article publication date: 5 June 2017

Abstract

Purpose

The purpose of this paper was to investigate the corrosion behaviour of API X65 pipeline steel in the simulated CO2/oil/water emulsion using weight loss technique, potentiodynamic polarization technique and characterization of the corroded surface techniques.

Design/methodology/approach

The weight loss analysis, electrochemical study and surface investigation were carried out on API X65 pipeline steel that had been immersed in the CO2/oil/water corrosive medium to understand the corrosion behaviour of gathering pipeline steel. The weight loss tests were carried out in a 3L autoclave, and effects of temperature, CO2 partial pressure, water cut and flow velocity on the CO2 corrosion rate of API X65 pipeline steel were studied. Electrochemical studies were carried out in a three-electrode electrochemical cell with the test temperature was 60°C, and the CO2 partial pressure was 1 atm by recording open circuit potential/time and potentiodynamic polarization characteristics. The surface and cross-sectional morphologies of corrosion product scales were characterized using scanning electron microscopy. The phases of corrosion product scales were investigated using X-ray diffraction.

Findings

The results showed that water cut was the main controlling factor of API X65 steel corrosion under the conditions of CO2/oil/water multiphase flow, and it had significant impact on corrosion morphology. In the case of higher water cut or pure water phase, general corrosion occurred on the steel surface. While water cut was below 70 per cent, corrosion morphology transformed into localized corrosion, crude oil decreased corrosion rate significantly and played a role of inhibitor. Crude oil hindered the corrosion scales from being dissolved by corrosive medium and changed dimension and accumulation pattern of the crystal grain, thickness and structure of the corrosion scales; thus, it influenced the corrosion rate. The primary corrosion product of API X65 steel was ferrous carbonate, which could act as a protective film at low water cut so that the corrosion rate can be reduced.

Originality/value

The results can be helpful in selecting the suitable corrosion inhibitors and targeted anti-corrosion measures for CO2/oil/water corrosive environment.

Keywords

Acknowledgements

The authors would like to express their thanks to Professor Zili Li (Department of Oil & Gas Storage and Transportation Engineering, China University of Petroleum) for his help. The work was supported by the National Science and Technology Major Project of China (2011ZX 05,017-004). It was also supported by the National Natural Science Foundation of China (51301201).

Citation

Cheng, Y., Li, Z., Zhao, Y., Xu, Y., Liu, Q. and Bai, Y. (2017), "Effect of main controlling factor on the corrosion behaviour of API X65 pipeline steel in the CO2/oil/water environment", Anti-Corrosion Methods and Materials, Vol. 64 No. 4, pp. 371-379. https://doi.org/10.1108/ACMM-04-2016-1665

Publisher

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Emerald Publishing Limited

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