Stress Corrosion Cracking Behavior of X80 Pipeline Steel in Acid Soil Environment with SRB
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INTRODUCTION
MICROBIOLOGICALLY induced corrosion (MIC) is the corrosion and destruction induced by microbial metabolic activity, which is the most widespread in soil, ocean, and oil field environment.[1–3] Sulphate-reducing bacteria (SRB) are one of the most primary factors causing the MIC.[4–6] Currently, the electrochemical behavior of metal corrosion induced by SRB has been widely studied by researchers locally and internationally, focusing on two aspects of cognition. Firstly, SRB can utilize organic nutrition attachment to the steel surface as carbon source and reduce sulphate to hydrogen sulphide and sulphide, thereby promoting metal corrosion.[7–9] Secondly, SRB can consume cathode hydrogen via hydrogenated enzyme and accelerate metal corrosion.[10,11] In April 2004, an oil leakage accident occurred in an API 5L X52 pipeline in the north of Iran; survey showed the simultaneous effects of SRB under pipe coating, and soil environment is responsible for the stress corrosion cracking (SCC).[12] Consequently, the SCC behavior of pipeline steel in the presence of SRB has attracted our attention. However, to the best of our knowledge, investigations on the SCC behavior of pipeline steel in soil solution with SRB are few;[13] specifically, studies regarding the SCC behavior
of high-strength pipeline steel in actual soil environment have not been reported yet. A large number of X80 pipeline steels are used in West–East Gas Pipeline Project via Yingtan of Jiangxi province at about 57 Km. Yingtan soil is a typical acid red soil of southeast of China, where the pH value is between 3 and 6. SCC easily occurs in this area, which exhibits high water content and low oxygen content.[14,15] Therefore, the stress corrosion behavior and mechanism of X80 pipeline steel in acid soil environment with SRB should be investigated. This study aims to investigate the SCC behavior of X80 pipeline steels with self-designed ‘stress electrochemical corrosion testing device’,[16] which can support the normal growth and metabolism of SRB, and measure the electrochemical properties in the SCC process of metals. The study of SCC behavior mechanism of X80 pipeline steel in acid soil environment with SRB can provide scientific reference for protection of X80 pipeline steel from SCC in typical acid soil environment in China.
II.
EXPERIMENTAL
A. Testing Medium
DAN WANG, FEI XIE, MING WU, YUE ZONG, and XUE LI are with the Key Laboratory of Oil & Gas Storage and Transportation, College of Petroleum Engineering, Liaoning Shihua University, No. 1, Dandong Road, Fushun, Liaoning 113001, China. Contact e-mail: [email protected] GUANGXIN LIU is with the Key Laboratory of Oil & Gas Storage and Transportation, College of Petroleum Engineering, Liaoning Shihua University and also with the College of Pipeline and Civil Engineering, China University of Petroleum, Qingdao, Shandong 266555, China. Manuscript submitted on October 23, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
The Yingtan soil used in this study was collected at 1 m below ground of Yingt
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