温度对X70管线钢在含氧溶液中应力腐蚀的影响

Effects of temperature on stress corrosion of X70 pipeline steel in solution with oxygen

通过扫描电镜观察X70管线钢表面铁素体微观形貌,采用能谱仪分析其化学元素质量分数。在常温及60℃时,采用慢应变速率法(SSRT),分别在空气和氧质量分数为1.0×10-4的NACE(Na C1与CH3COOH质量分数分别为5%和0.5%)溶液中进行X70管线钢应力腐蚀试验,对试样断口形貌进行分析,并研究温度对X70管线钢在氧质量分数为1.0×10-4溶液中应力腐蚀开裂(SSCC)敏感性的影响。研究结果表明:常温下X70管线钢应力腐蚀敏感性不明显,当温度升至60℃时应力腐蚀敏感性增加,有应力腐蚀倾向;氧元素对试样应力腐蚀性能有一定的促进作用,60℃时NACE溶液中Cl-与O2运动加剧,是应力腐蚀敏感性增强的重要因素。

The ferrite morphology of the X70 pipeline steel surface was observed with metallographic microscope, and the content of chemical elements of X70 pipeline steel was analyzed with energy disperse spectroscopy. The stress corrosions of X70 pipeline in NACE （5% NaCl＋0.5% CH3COOH, mass fraction） solution （with oxygen mass fraction of 1 × 10-4） or air medium were tested with slow strain rate testing （SSRT） at room temperature and 60 ℃, respectively. The fracture morphologies of the specimens were analyzed, the effect of temperature on stress corrosion cracking （SCC） sensitivity of X70 pipeline steel in the solution was studied, and the oxygen content in the solution was 1.0× 10-4 （mass fraction）. The results show that the stress corrosion phenomenon is not obvious at room temperature. When the temperature increases to 60 ℃, the stress corrosion sensitivity increases obviously, and has a tendency to stress corrosion, as oxygen element plays a certain role in promoting the performance of stress corrosion. The movement of C1 and 02 is faster in NACE solution at 60 ℃, which leads to the change of stress corrosion sensitivity.