Cl^-和极化电位对X70钢缝隙腐蚀行为的影响

Influence of Cl^- and Polarization Potential on Crevice Corrosion Behavior of X70 Pipeline Steel

采用恒电位极化方法研究了X70钢在NaHCO_3溶液中的缝隙腐蚀行为,分析了Cl^-浓度和极化电位对X70钢缝隙腐蚀萌生及发展的影响,探讨了X70钢在NaHCO_3溶液中的缝隙腐蚀机理。结果表明:在-0.4V恒电位极化下,缝隙内X70钢在NaHCO_3溶液中可以发生局部腐蚀。缝口处首先发生酸化,并逐渐往缝底扩展。随着腐蚀的发展,酸化加剧,后期发生析氢反应,阴极反应由溶解氧的还原转变为H+的还原。加入Cl^-不改变缝内X70钢的腐蚀机理,但随着Cl^-浓度的增大,缝内腐蚀速率增加。随着极化电位的提高,缝隙内X70钢的腐蚀部位逐渐往缝底移动,同时发生点蚀。而缝隙腐蚀的萌生区域由极化电位及电位下降的程度决定。

The crevice corrosion behavior of X70 pipeline steel in Na HCO3 solution with varying Cl^- concentration was investigated by potentiostatic polarization method in terms of the initiation and development of crevice corrosion. Results show that inside the crevice the X70 steel could suffer from localized corrosion in Na HCO3 solution by polarization potential-0.4 V. The acidification initiated firstly at the crevice mouth and then extended gradually to the bottom. The hydrogen evolution could be observed with the development of corrosion and acidification. The cathodic reaction changed from the reduction of the dissolved oxygen to the reduction of hydrogen ions. The presence of Cl^- did not change the crevice corrosion mechanism. With the increase of Cl^- concentration, however, the crevice corrosion rate increased. The corrosion region moved towards the crevice bottom gradually and then pitting corrosion occurred with the increasing polarization potential.The initiation of crevice corrosion was determined by the polarization potential.