不同温度下H_2S/CO_2腐蚀产物膜对T95套管腐蚀行为的影响

Effects of H_2S/CO_2 Corrosion Scale on Corrosion Behavior of T95 Casing Steel at Different Temperature

目的探究不同温度下H_2S/CO_2腐蚀产物膜对T95钢腐蚀行为的影响。方法将T95油管钢切割成15 mm×10 mm×3 mm的规格,表面经抛光打磨后,利用千分尺测量具体尺寸,用AR2140电子天平称量。试片分别垂直置于上支架与下支架,下支架平稳放入釜底,而后加入模拟地层水,确保实验介质浸没下支架试样而不与上部挂片试样接触。在气密性良好的基础上连续2 h通入N_2除氧,而后顺序通入H_2S、CO_2和N_2,并升温升压至实验要求。72 h后将试样从气、液相中取出,分别取样采用电子显微镜观察腐蚀产物膜的微观形态,并利用X射线能谱仪分析腐蚀产物膜的成分,并计算去除腐蚀产物后试样在气相/液相中的腐蚀速率。结果 T95试件在H_2S/CO_2的液相环境中的腐蚀速率整体比气相环境大,这可能是因为液相腐蚀产物膜较气相腐蚀产物膜疏松。温度对H_2S/CO_2腐蚀产物膜的形成具有重要影响,随着温度的升高,H_2S/CO_2腐蚀产物膜逐渐变厚,但成膜效果变差,高温下的腐蚀产物膜具有一定保护作用而使得腐蚀速率增大的幅度变缓。T95钢腐蚀产物膜的主要成分是FexSy系列化合物和FeCO_3,同时还形成Cr(OH)_3和Cr_2O_3非晶态产物,这些产物起到了阻隔阴离子穿透腐蚀产物膜的作用,使与金属基体界面接触的阴离子溶度降低,抑制了金属基体的阳极反应而减小腐蚀速率。而形成的腐蚀产物膜,造成界面反应的时间常数和Rt值明显增大,一定程度上阻碍腐蚀的继续发展。结论温度对H_2S/CO_2腐蚀产物膜的形成具有重要影响,H_2S/CO_2腐蚀产物膜随着温度的升高逐渐变厚,但成膜效果变差,温度大于120℃时,腐蚀产物膜具有一定的保护作用而使得腐蚀速率增大的幅度变缓。

The work aims to explore the effects of H_2S/CO_2 corrosion scale on corrosion behavior of T95 casing steel at different temperature. T95 steel was cut into 15 mm×10 mm×3 mm specification, and its specific size was measured by using micrometer and weighed with AR2140 electronic balance after surface polishing. The test blocks were placed on the upper and lower brackets vertically, and the lower bracket was put on the bottom of the kettle steadily, then simulated formation water was filled. It was necessary to ensure that sample on the lower bracket was immersed by test medium without contacting with sample on the upper bracket. Provided with good air tightness, H_2S, CO_2 and N_2 were supplied in turn after filling with N_2 continuosly for 2 h for oxygen removal, and then temperature and pressure were improved to meet experimental requirements. The samples were taken out from gaseous and liquid phases after 72 h, the microscopic morphology of corrosion scale was observed under an electron microscope by sampling. Compositions of the corrosion scale were analyzed by X-ray energy spectrometer. Corrosion rate of samples in gaseous/liquid phases after removing corrosion products was calculated. The corrosion rate of T95 casing steel in liquid phase of H_2S/CO_2 was higher than that in gas phase, which might result from that the liquid corrosion scale was more porous than the gaseous corrosion scale. Temperature had great influence on formation of H_2S/CO_2 corrosion scale which became thicker as temperature increased while the film-forming effect became worse. The corrosion scale at high temperature had protective effect so that the increase of corrosion rate slowed down graduallly. The major components of corrosion scale on T95 steel was FexSy serial compounds and FeCO_3. Meanwhile, Cr（OH）_3 and Cr_2O_3 non-amorphous products were also generated to prevent anions from penetrating into the corrosion scale, reduce anion solution contacting with metal substrate interface, inhibit anodic reaction and further decrease the corrosion rate. Forming of corrosion scale resulted in significant increase of time constant and Rt value of interface reaction, which hindered further development of corrosion to a certain extent. Temperature has great influence on the formation of H_2S/CO_2 corrosion scale which becomes thicker as temperature increases while the film-forming effect becomes worse. When temperature exceeds 120 ℃, the corrosion scale has protective effect so that the increase of corrosion rate slows down graduallly.