CO2腐蚀产物膜的微观形貌和结构特征

研究了碳钢、低Cr钢在不同条件下形成CO2腐蚀产物膜的微观形貌、成分和结构特征.结果表明,N80(碳钢)、1Cr-L80形成的腐蚀产物膜主要由FeCO3晶体堆垛而成,而3Cr-L80、5Cr-L80的表层则形成大面积的含Cr化合物,主要为Cr(OH)3和Cr2O3.这些Cr的化合物脱水后比较疏松,容易形成龟裂.在静态条件下,碳钢和含Cr钢的腐蚀产物膜均具有分层结构,碳钢外层与内层腐蚀产物膜的成分变化不大,主要为Fe、Ca碳酸复盐.含Cr钢的内层腐蚀产物膜中出现Cr元素的富集,外层主要为Fe、Ca碳酸复盐.随着Cr含量的增加,材料的腐蚀产物膜向非晶态转变.在静态条件下,低Cr钢比碳钢的腐蚀速率稍大;在动态(1.5 m/s)条件下,含Cr钢的腐蚀速率明显低于碳钢,而且腐蚀速率随着Cr含量的增加而下降.

Morphology and microstructure of CO2 corrosion scales

The morphology and microstructure of the CO2 corrosion scales formed under different conditions were investigated by means of SEM, EDS, XRD in this paper. A typical FeCO3 crystalline was observed in the scales of N80 (carbon steel) and lCr-L80 while chromium compounds were formed on the surface of 3Cr-L80 and 5G-L80. These chromium compounds were confirmed as Cr(OH)3 and Cr2O03. They were loose and formed chaps after dehydration. Under the static condition, the scales of carbon steel and chromium-containing steels all had delamination structure. There were similar compositions between outer and inner scales of carbon steel in the form of (Fe, Ca)CO3. Chromium enrichment in the inner scales of chromium-containing steels was observed with the surface scale presented as (Fe, Ca)CO3. XRD patterns of the scales formed under dynamic condition indicated that the scales of chromium-containing steels gradually translated into amorphous structure with the increase of chromium content. The weight-loss testing results showed that the corrosion rate of chromium-containing steels approached to carbon steel under static condition, while under dynamic condition (1.5 m/s), the corrosion rates of chromium-containing steels were much less than that of carbon steel. And the corrosion rates decreased with the increase of chromium content.