J55钢CO_2腐蚀产物膜形貌结构研究

STUDY OF CO_2 CORROSION SCALE ON J55 STEEL SURFACE

在高温高压静态釜中进行了J55油套管钢的CO2 腐蚀模拟试验,并对其腐蚀试样进行了磨损试验,得到腐蚀膜不同厚度的层面。用X射线衍射仪(XRD)和电子散射能谱仪(EDS)分析了膜的化学组成;用扫描电镜(SEM)分析了腐蚀产物膜的不同层面形貌、断面形貌以及厚度或表面晶粒大小与温度或CO2 分压之间的关系。结果显示,在模拟试验条件下,J55钢所得到深褐色的腐蚀膜断面形貌为双层结构,表层为粗大而较规则的晶粒,内层膜为类似泥浆状的细小晶粒薄层;膜的主要成分为FeCO3,温度>180℃的腐蚀膜也未检测到各种铁的氧化物,在内层膜中检测出少量的Fe3C。膜厚和晶粒大小随着温度变化的极大值均在120℃处,极小值在 160℃处,但两者曲线稍有不同。CO2 分压对膜厚和晶粒大小的影响较复杂,在CO2 分压为 6.89MPa时,膜厚和晶粒均达到极大值;另一个极大值晶粒在3 45MPa,膜厚在2.41MPa;在两极大值之间,出现一极小值,晶粒在4.13MPa,膜厚在3.45MPa;在临界压力以上,晶粒大小或膜厚均急剧减小。

Autoclave is employed to simulate the corrosion for J55 steel in CO_2 environments and to study its corrosion process. The corrosion samples are wore in self-made wearing equipment to gain various corrosion scales, and they are used to observe their surface and profiles with Scanning Electron Microscope (SEM), and their phase structures and chemical composition are analyzed by X-ray diffraction (XRD) and X-ray Energy Dispersive Spectrometry (EDS). The effect of temperature or CO_2 pressure on the average thickness and grain size of the scales is studied in this paper. The results show that, the puce scales are double-layers in the cross-section, which is more bulky and more regular grains on the outer scale but finer grain scale alike dried slurry in inner scale. The major chemical composition of the scale is ferrous carbonate, and other iron oxides are not observed in the scale even gained at 180℃. And also a small quantity of cementite is found in inner scale besides the ferrous carbonate. The variation of average thickness and surface grain size of the scale for J55 steels with respect to the temperature reaches all the maximum values at 120℃, and the minimum at 160℃, but there is a little difference between twocurves. The variation with respect to the CO_2 pressure at 90℃ reaches all one maximum value at 6.89MPa, the other one at 3.45MPa for grain size and at 2.41MPa for scale thickness. There is a minimum value between two maximum, at 4.13MPa for surface grain size and at 3.45MPa for scale thickness, respectively. When CO_2 pressure is higher than 6.89MPa, grain size and scale thickness decrease rapidly.