1) Corrosion and Protection Center, University of Science and Technology Beijing, Beijing 100083, China. 2) Key Laboratory for Corrosion and Protection (MOE), Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China. 3) Ningbo Institute of Material Technology & Engineering, Chinese Academy of Sciences, Ningbo 315201, China;
Cite this article:
Zhiyong LIU,Zongshu LI,Xiaolin ZHAN,Wenzhu HUANGFU,Cuiwei DU,Xiaogang LI. GROWTH BEHAVIOR AND MECHANISM OF STRESS CORROSION CRACKS OF X80 PIPELINE STEEL IN SIMULATED YINGTAN SOIL SOLUTION. Acta Metall Sin, 2016, 52(8): 965-972.
Stress corrosion cracking (SCC) in soil environments is one of the major failure and accident causes for oil and gas pipelines, which have induced hundreds of damages all over the world, resulting in serious economic losses and casualties. Previous study showed that acidic soil environments in Southeast of China are highly sensitive to SCC of pipeline steels. However, there is less research on the behavior and mechanism of growth behavior of SCC in this environment up to date. SCC behavior and mechanism of X80 pipeline steel in the simulated solution of Yingtan in China was investigated with electrochemical polarization curves, EIS, slow-rate-loading crack-growth test and SEM. Results showed that the applied polarization potential played an important role in SCC growth behavior and mechanism of X80 pipeline steel in the simulated solution of the acid soil environment. With the decreasing of the applied potential, the crack propagation rate increased constantly. In comparison to the crack propagation at the open circuit potential, the cracks extended faster in the initial stage of crack propagation when the applied potential was -850 mV; nevertheless, in the rapid propagation stage, the rate of the propagation was magnified with the application of -1200 mV potential. In addition, the crack propagation mode varied with applied potentials: it was mixed-controlled by both anodic dissolution (AD) and hydrogen embrittlement (HE) when the applied potential was more positive than -930 mV, and only in control of HE when the potential was less than -930 mV.
Fund: Supported by National Basic Research Program of China (No.2014CB643300), National Natural Science Foundation of China (Nos.51371036, 51131001 and 51471034) and Beijing Higher Education Young Elite Teacher Project
Fig.1 Schematic of specimen for slow-rate-loading crack growth test (unit: mm)
Fig.2 Schematic of crack extension test apparatus
Fig.3 Fast (50 mVs-1) and slow (0.5 mVs-1) scanning rate polarization curves of X80 pipeline steel in the simulated soil solution
Fig.4 Nyquist (a) and Bode (b) plots of X80 pipeline steel in simulated Yingtan soil solution at different potentials (Inset in Fig.4a shows the enlarged view; OCP: open circuit potential)
Fig.5 Equivalent circuits of EIS of X80 pipeline steel in simulated soil solution at different potentials (Rsol—solution resistance, Rf—corrosion product film resistance, Rt—charge transfer resisitance, Qf—corrosion product capacitance, Qdl—double-layer capacitance)
Fig.6 Stress-time curves of X80 pipeline steel in simulated soil solution at different applied potentials
Fig.7 Current (I)-time curves of X80 steel in simulated soil solution at applied constant potentials of -850 mV (a) and -1200 mV (b)
Fig.8 Variation of crack propagation length with test time of X80 pipeline steel in simulated soil solution at different potentials
Fig.9 Variation of crack propagation rate with test time of X80 pipeline steel in simulated soil solution at different potentials
Fig.10 SEM images of X80 pipeline steel in simulated soil solution with applied potentials of OCP (a, a1), -850 mV (b,b1) and -1200 mV (c, c1) (Figs.10a1~c1 correspond to magnified views of rectangle areas in Figs.10a~c, respectively)
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