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Effect of deteriorated microstructures on stress corrosion cracking of X70 pipeline steel in acidic soil environment

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Journal of University of Science and Technology Beijing 2008年第6期15卷 707-713页

作者： zhiyong liu guoli zhai xiaogang li cuiwei du Corrosion and Protection Center University of Science and Technology Beijing Beijing 100083 China

In order to investigate stress corrosion cracking （SCC） of X70 pipeline steel and its weld joint area in acidic soil environ- ment in China, two simulating methods were used： one was to obtain bad microstructures in heat affected zone by annealing at 1300 ℃ for 10 min and then, quenching in water; the other was to get different simulating solutions of acidic soil in Yingtan in south- east China. The SCC susceptibilities of X70 pipeline steel before and after quenching in the simulating solutions were analyzed using slow stain rate test （SSRT） and potentiodynamic polarization technique to investigate the SCC electrochemical mechanism of different microstructures further. The results show that SCC appears in the original microstructure and the quenched microstructure as the polarization potential decreases. Hydrogen revolution accelerates SCC of the two tested materials within the range of-850 mV to -1200 mV vs. SCE. Microstructural hardening and grain coarsening also increase SCC. The SCC mechanisms are different, anodic dissolution is the key of causing SCC as the polarization potential is higher than the null current potential, and hydrogen embrittlement will play a more important role to SCC as the polarization potential lower than the null current potential.

关键词： X70 steel heat affected zone heat treatment stress corrosion cracking (SCC) acidic soil environment

Relationship between electrochemical characteristics and SCC of X70 pipeline steel in an acidic soil simulated solution

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Acta Metallurgica Sinica(English Letters) 2009年第1期22卷 58-64页

作者： zhiyong liu xiaogang li Yingrui ZHANG cuiwei du guoli ZHA Key Lab of Corrosion Erosion and Surface Technique Beijing Corrosion and Protection Center University of Science and Technology Beijing Beijing 100083 China Mechanical Engineering Department University of Rochester NY 14627 USA

Stress corrosion cracking （SCC） of X70 pipeline steel in simulated solution of the acidic soil in Yingtan in China was investigated using slow strain rate test （SSRT）, SEM and potentiodynamic polarization technique. Experiment results indicate that X70 steel is highly susceptible to SCC as applied potential reduces, which is manifested in loss of toughness and brittle fracture. Constaat polarization current can detect the occurrence of SCC. The lower the polarization current is the sooner stress corrosion cracking occurs. The SCC mechanisms are different at varying potentials. When potential is higher than open circuit potential, anodic process controls SCC, whereas when potential is far lower than open circuit potential, cathodic process controls SCC, and between these two potential regions, a combined electrochemical process controls the SCC. Stress or strain has a synergistic effect with electrochemical reactions to accelerate the cathodic hydrogen evolution process, which makes the X70 pipeline steel to be more susceptible to SCC.

关键词： X70 steel SCC Electrochemical process Acidic soil

X70钢在酸性土壤模拟溶液中的应力腐蚀行为

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金属学报 2008年第2期44卷 209-214页

作者：刘智勇翟国丽杜翠薇李晓刚北京科技大学腐蚀与防护中心北京市腐蚀、磨蚀与表面技术开放实验室北京100083

在不同的阴极保护电位下,采用慢应变速率拉伸实验、动电位极化方法以及SEM研究了X70钢在酸性土壤模拟溶液中的应力腐蚀行为.结果表明:X70钢发生穿晶应力腐蚀裂纹;应力腐蚀开裂(SCC)萌生与外加保护电位有关,完全受阳极过程控制时X70钢的... 详细信息

在不同的阴极保护电位下,采用慢应变速率拉伸实验、动电位极化方法以及SEM研究了X70钢在酸性土壤模拟溶液中的应力腐蚀行为.结果表明:X70钢发生穿晶应力腐蚀裂纹;应力腐蚀开裂(SCC)萌生与外加保护电位有关,完全受阳极过程控制时X70钢的SCC敏感性较低,但会发生点蚀和严重的均匀腐蚀;受混合电极过程控制和全受阴极过程控制时均能发生SCC;受混合电极过程控制时,SCC二次裂纹与点蚀伴生,裂纹形核密度大;而完全受阴极过程控制时,SCC裂纹附近未见点蚀坑,裂纹形核密度低;混合电极过程控制时比完全阴极电极过程控制下更容易发生SCC裂纹.

关键词： XTO钢应力腐蚀开裂酸性土壤模拟溶液