碳酸钠-碳酸氢钠溶液中X-42钢楔形缝隙内的电位和pH值

Distribution of Potential and pH Value in Wedge-Shaped Crevice on Piping Steel X-42 in Sodium Carbonate-Sodium Bicarbonate Solution

埋地管道的涂覆层因损伤而开裂起翘 ,是引发其点蚀穿孔和应力腐蚀断裂的主要原因之一。为此 ,在自行设计的模拟涂覆层开裂起翘楔形缝隙的装置上 ,分别测量了缝隙开口宽度为 0 .1,0 .2 ,0 .3mm时管道钢X - 4 2在0 .5mol/LNa2 CO3 +1mol/LNaHCO3 溶液中缝隙内的电极电位、溶液pH值分布 ,讨论了缝隙开口宽度对电极电位、溶液pH值分布的影响。结果表明 ,在自然腐蚀试验条件下 ,楔形缝隙内自缝口向缝尖电极电位呈负移态势 ,pH值呈下降态势 ;0 .1mm的缝隙开口宽度具有更大的闭塞性 ,产生更为明显的缝隙腐蚀敏感性 ;当缝隙开口大于 0 .2mm时 ,10 0h内缝内金属未发生腐蚀。

Crack and shelling of coatings on underground pipeline is one of the main reasons for pitting corrosion and stress corrosion cracking of the pipeline. A self-made wedge-shaped crevice simulated shelling of coatings was designed to investigate the distribution of potential and pH value in the wedge-shaped crevice made of steel X-42 with the gap was 0. 1 mm, 0. 2 mm, 0. 3 mm separately in 0. 5 mol/L Na 2CO 3 + 1 mol/L NaHCO 3 solution. The effect of gap width on these parameters was also discussed. The results show that under the open corrosion condition the potential and the pH value of solution in the crevice decreased with the distance from the mouth of the crevice. And the crevice with 0. 1 mm gab has the most occlusive effect that results in the strongest sensitivity to crevice corrosion of metal. The metal in the crevice is without corrosion in 100 hour as the gap width is bigger than 0. 2 mm.