Issue 50

Z.-y. Han et alii, Frattura ed Integrità Strutturale, 50 (2019) 21-28; DOI: 10.3221/IGF-ESIS.50.03 20 Stress corrosion behavior of X80 pipeline steel in the natural seawater with different dissolved oxygen contents Zhong-ying Han School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, 266580, China. hanzhying@upc.edu.cn Xiao-guang Huang College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao, 266580, China. huangxg@upc.edu.cn A BSTRACT . Stress corrosion slow strain rate tensile tests of the X80 steel in the natural seawater are carried out to study the effect of dissolved oxygen (DO) on the sensitivity of stress corrosion. Scanning electron microscope (SEM) combined with the electrochemical measurement is adopted to analyze the mechanism and affecting factor of the stress corrosion cracking (SCC). The results show that the sensitivity of SCC in the natural seawater increases and the stress corrosion cracking gradually transforms from ductile to quasi- brittle fracture, with the increase of dissolved oxygen content. Tafle polarization curves and electrochemical impedance spectroscopy of X80 steel show that the dissolved oxygen aggravates the electrochemical corrosion and reduces the corrosion resistance. The corrosion pits and micro cracks at the lateral and fracture surface trigger the stress concentration and promote the anodic dissolution under the applied stress, thereby accelerate the process of stress corrosion cracking of the X80 steel. K EYWORDS . Stress corrosion; Dissolved oxygen; Sensitivity; Stress concentration; Anodic dissolution. Citation: Han, Z. Y., Huang, X. G., Stress corrosion behavior of X80 pipeline steel in natural seawater with different dissolved oxygen, Frattura ed Integrità Strutturale, 50 (2019) 20-28. Received: 11.04.2018 Accepted: 07.07.2019 Published: 01.10.2019 Copyright: © 2019 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION ubmarine pipeline is an indispensable part and the lifeline of offshore oil-gas exploitation. During the laying and service period, submarine pipelines are often subjected to various loadings, such as the internal pressure, temperature, bending, and wave and flow [1-2]. Under the interaction of these external loadings, the inner and outer coatings of pipeline are easy to break or fall off. Once the seawater penetrates, the corrosion of pipeline is inevitable. The coupling effect of corrosion and stress is easy to induce the stress corrosion failure even under very lower stress and this greatly shortens the service life of the pipeline [3-4]. Rupture of the pipeline and the accompanying oil leakage often result in a S