B_2/DO_3热处理对Fe_3Al基合金在湿H_2S-CO_2-Cl^-环境中耐蚀性的影响

Effect of B_2/DO_3 heat treatment on corrosion resistance of Fe_3Al matrix alloy in H_2S-CO_2-Cl^- environment

针对不同结构对Fe_3Al合金在湿H_2S-CO_2-Cl^-天然气集输环境中耐蚀性的影响,对未处理、经B_2或DO_3热处理的Fe_3Al试样,遵循ASTM G111-97(2013)和NACE TM 0169/G31-12a标准,试验模拟罗家寨气田实际工况进行全浸均匀腐蚀试验,评估其腐蚀速率;采用XRD表征其物相;采用SEM表征其腐蚀前后表面的微观结构;采用EDS测量并统计分析不同结构位置化学成分的差异。结果表明,Fe-28Al-4Cr合金(原子分数,%)在所模拟罗家寨气田实际工况环境中,经168 h后合金表面形成内层以铝氧化物+铁氧化物为主、外层以铁氧化物+铁硫化物为主的双层腐蚀产物膜,内层膜致密而均匀,但受金属基体表面形貌影响会发生开裂。Fe-28Al-4Cr合金表面DO_3结构比B_2结构Fe含量约低1.75at%,而Al含量约高1.64at%。内层腐蚀产物膜主要构成元素Al含量的不同,使合金表面钝化膜生长行为产生差异,进而影响合金耐蚀性;具体表现为2~24 h内因钝化DO_3处理合金的腐蚀速率下降响应更迅速。在所模拟罗家寨气田实际工况环境中,168 h后Fe-28Al-4Cr合金腐蚀速率趋于稳定,为0.238~0.27 mm/y,均达到了实际工程应用的条件。

Aimed at gaining an insight into the effects of heat treatment on corrosion resistance of Fe_3 Al alloy in wet natural gas,which is a H_2S-CO_2-Cl^-environment,samples in original state,after B_2 or DO_3heat treatment were prepared,corrosion tests in simulated environment of Luojiazhai gas field were performed on these samples according to ASTM G111-97（ 2013） NACE TM 0169/G31-12a; XRD,SEM,and EDS were employed to investigate phases,microstructure before or after corroding and composition differences between variety microstructures in samples,respectively. The results indicate that a stable bilayer film are formed on Fe-28Al-4Cr alloy（ atom fraction,%） after immersed in simulated environment of Luojiazhai gas field,which is composed of aluminum oxide ＋ iron oxide based inner layer and iron oxide ＋ iron sulfide based external layer. The inner layer is uniform and dense,which may crack on account of metal matrix＇s morphology. B_2 structures exhibit higher surface Fe-content,at about 1. 75at%,than DO_3 structure in Fe-28Al-4Cr,while DO_3 structure have a higher surface Al-content,at around 1. 64at%. The surface Al-content,which is the major layer former element,leads to differences in film growth behavior,then result in effects on corrosion resistant. Such as the corrosion rate of Fe-28Al-4Cr alloy treated by DO_3 has reduced sharply during immersion for 2-24 h. The corrosion rate of the alloy has stabilized at 0. 238-0. 27 mm/y after immersion in simulated environment of Luojiazhai gas field for 168 h,which are all satisfied for practical engineering applications.