管线钢高pH值应力腐蚀裂纹研究

Study on High pH Stress Corrosion Cracking(SCC) of Pipeline Steel

许多油气管道断裂事故与管道外表面的应力腐蚀开裂(SCC)有关。对高pH值溶液中的16Mn钢和X70管线钢分别进行了电化学测试和拉伸试验,利用动电位极化曲线测试得到了快慢扫描极化曲线(慢扫描速度20 mV/min,快扫描速度1 000 mV/min),根据它们的差值确定了16Mn钢和X70管线钢对高pH值应力腐蚀开裂敏感的电位。结果表明,环境温度对敏感电位的影响较大,随温度的升高,扩大了敏感电位区间。在高pH值应力腐蚀敏感电位(-600 mV SCE)下,恒定加载试样应力到管材屈服极限的70%,试样表面未出现表面开裂;而在间断加载条件下,在颈缩区表面出现了裂纹,说明载荷的波动是高pH值应力腐蚀裂纹萌生的必要条件,且高pH值应力腐蚀开裂易发生在塑性变形和应力集中处。

Many breakage accidents of oil ＆ gas pipeline are linked with SCC of pipeline outshte surface . In this article, electrochemical testing and tensile test were conducted on 16Mn and X70 pipeline steels respectively. The slow and rapid sweep rate curves （slow sweep rale 20 mV/min, rapid sweep rate 1 000 mV/min） were obtained by potentiodynamie polarization curve tests, and the potential range sensitive to high pH SCC was determined by difference value of the slow and rapid sweep curves. The resuh showed Ihat environment temperature greatly affect the potentials sensitive to high pH SCC. The higher the temperature is, the wider the sensitiw~ potenlial range is. Under the potential sensitive to SCC（~O0 mV SCE）, specimens at~ loaded ennstantly to 70~/~ of yiehl limit of Inateri^3.1, no cracking oet＇m~ on the specimen surface. Under intermittent loading, cracks appear on the surface in the necking area. The experiment results indieated that the fluctuation of the load is necessary to the initiation of high ptt SCC, and the high pit SCC oeeurs easily in the, position where plastic detormation or stress concentration.