低铬X65管线钢CO2腐蚀产物膜的特征及形成机制

CHARACTERISTICS AND FORMATION MECHANISM OF CORROSION SCALES ON LOW-CHROMIUM X65 STEELS IN CO_2 ENVIRONMENT

利用高温高压CO_2腐蚀模拟实验以及ESEM,EDS,XPS和SEM等分析技术,研究了4种不同含Cr量的X65管线钢的腐蚀速率、腐蚀形态和腐蚀产物膜结构特征.结果表明:含Cr量高的钢平均腐蚀速率小,无Cr和含1%Cr的钢的腐蚀形态为局部腐蚀,含3%和5%Cr的钢的腐蚀形态为全面腐蚀.在高温高压CO_2腐蚀环境中,含Cr钢的腐蚀产物膜为FeCO_3和Cr(OH)_3竞争沉积形成的多层结构,其中1Cr-X65和3Cr-X65的腐蚀膜具有3层结构,5Cr-X65的腐蚀膜是双层结构.Cr在腐蚀产物膜层中出现局部富集,远高于基体中的Cr含量.高含Cr量使腐蚀产物膜中的Cr(OH)_3含量高,并提高了腐蚀膜的保护性能,从而引起腐蚀形态发生转变,腐蚀速率降低.FeCO_3和Cr(OH)_3共沉积层膜对低铬钢的抗CO_2腐蚀性能具有关键的影响.

The corrosion rates of X65 steels with different Cr contents were measured in CO2 environment under high temperature and high pressure condition. ESEM, EDS, XPS and SEM were employed to analyze the morphologies and characteristics of corrosion scales on the steels. The results show that the corrosion rate significantly decreased with increasing Cr content in the steels. An increase in Cr content leads to a lower susceptibility to local corrosion. When the Cr content reaches up to 3%, the local corrosion can be eliminated. The competitive deposition of FeCO3 and Cr（OH）3 on low-chromium steels results in a multilayer structure of the scales. The scales on 1Cr-X65 and 3Cr-X65 steels have three-layer structure and scale on 5Cr-X65 steel has two-layer structure. Cr exists mainly as amorphous compound Cr（OH）3 in specific layer of the corrosion scales on low-chromium X65 steels. The Cr（OH）3 content of the scale increases remarkably with increasing Cr content in the steels. The high Cr（OH）3 content improves the protection performance of the scales and the corrosion resistance of low-chromium X65 steels. The rate of general corrosion and susceptibility to local corrosion are mainly dependent on the formation of codeposition layer of FeCO3 with Cr（OH）3 on low-chromium steels.