Aiming at the effect of temperature on the minimum cathodic protection potential, the minimum cathodic protection potential of the buried pipeline L450 in the simulated soil solution under different temperature conditions was investigated through the tests of potentiodynamic polarization and potentiostatic polarization, and the technical means such as weight loss method and anodic Tafel straight-line segment back-propagation method for achieving the best protection state of cathodic protection system, avoiding the phenomenon of pipeline corrosion perforation caused by insufficient cathodic protection and thus improving the applicability and correctness of pipeline corrosion protection scientifically and effectively. Results showed that for pipelines with operating temperature ≤40 ℃, the minimum cathodic protection potential should be EP ≤-850 mV(vs CSE, the same below). For pipelines with operating temperature ranging from 40 ℃ to 60 ℃, the minimum cathodic protection potential should be-850 mV≤EP≤-950 mV. For pipelines with operating temperature ranging from 60 ℃ to 80 ℃, the minimum cathode protection potential should be-950 mV≤EP≤-1 000 mV. The pipelines with operating temperature ranging from >80 ℃ obtained EP≤-1 000 mV.
通过模拟不同Cl-浓度的腐蚀实验,结合EDS、SEM、EIS等分析手段,研究了T/S-52K直缝钢在不同Cl-浓度环境中的腐蚀行为。结果表明,随着Cl-浓度的增加,活化区域的阳极溶解加速,促进了试样表面的局部腐蚀,使得试样表面局部腐蚀严重;但随着腐蚀产物膜的覆盖,有效反应面积减小,所以试样的均匀腐蚀速率反而变化不大。当NaCl浓度为8 g/L时,T/S-52K直缝钢电极反应过程主要由扩散控制;当NaCl浓度为20 g/L时,T/S-52K直缝钢电极反应过程由扩散和活化共同控制;当NaCl浓度为35 g/L时,试样表面电极反应过程主要由活化极化所控制。
运用电化学技术,通过电极电位、耦合电流、交流阻抗图谱(EIS)测试分析,研究埋地保温管道破损点及远离破损点处的电化学腐蚀行为.结果表明:氧浓差导致破损点及远离破损点试样的电极电位出现明显差异,即破损点处电极电位较正,作为阴极,具有阴极保护效应,腐蚀速率仅为0.159 3 mm/a;远离破损点位置电极电位较负,作为阳极,具有接触腐蚀效应,腐蚀速率均高于破损点位置,最高为0.531 6 mm/a;受到模拟介质有效距离效应的影响,距离破损点最近位置试样的阳极电流密度最大,腐蚀最为严重;随着温度升高,阴极区与阳极区的电位差和耦合电流密度增大,远离破损点的阳极区腐蚀加剧.自腐蚀电位下T/S-52K管线钢的腐蚀具有阴极浓差极化控制为主的电极反应特征;防腐保温层破损后,破损点处具有明显O2扩散控制的阴极反应特征,而远离破损点位置具有明显活化极化控制的阳极反应特征;距破损点距离越近,电荷转移电阻越低(其中2#试样R1仅为430.2 Ω·cm2),金属离子化趋势越强.
为了解决高温稠油输送管道的腐蚀问题,通过典型稠油输送管道的外腐蚀分析,结合室内试验和现场测试,明确埋地保温稠油输送管道的腐蚀原因,进而提出相应的防治措施.结果表明:检测管段在补口位置未安装防水帽,搭接片处出现明显渗水痕迹,土壤水介质沿管道渗入导致整个渗水管段中下部发生较为严重的腐蚀.腐蚀最严重部位位于管道周向135°～180°,距补口渗水处10 cm,管道最小剩余壁厚为4.54 mm,最大点蚀深度为2.51 mm,底部力学性能显著降低;阴极保护电流屏蔽、最小阴极保护电位过高,以及管道服役时间过长、管输温度高是导致该稠油输送管道发生外腐蚀的主要原因.针对该高温稠油输送管道的腐蚀原因,从阴极保护实施方式和准则、防腐层材料选择、缓蚀剂防腐以及管输技术等方面,提出了相应防治措施,可以有效地解决相关问题,为管道的设计、建设、运营提供技术支撑.
