In this paper,a nickel based alloy Incoloy 825 (UNS NO8825) pipe with welding joints which had served for one year was cut and split to investigate its service status at the wellhead of a sour gas well and the formation mechanism of local corrosion pits on its internal surface.Microscopic morphologies of the pipe,welding joints,heat-affected zones and the cross section of the corroded grain boundary were observed by using a scanning electron microscope (SEM).And elements in the aforementioned areas were analyzed by virtue of an energy dispersive spectrometer (EDS).It is shown that,after the Incoloy 825 pipe is put into service,intergranular corrosion occurs on its surface and especially in local corrosion pits,but no deposits of any sulfide corrosion product are observed;that in the heat-affected zones,grains grow up and precipitated phase appears on the grain boundary,but no local corrosion is found;that the corrosion pits on the internal surface of Incoloy 825 pipe are caused by the over pickling in the process of pickling and passivation;that the Incoloy 825 pipe and the welding joints are corroded slightly during the service;that although the over pickling results in local corrosion on the internal surface of the pipe,the corrosion resistance of a passive film is improved after pickling and passivation;and that during the service of lncoloy 825 pipe which is pickled and passivated,the acidic environment with high temperature and high pressure has no corrosive effect or no extension of local corrosion.%为了研究镍基合金Incoloy 825 (UNS NO8825)管材在高含硫气井井口服役后内表面局部腐蚀坑的形成原因及其服役状况,截取并纵剖服役1年后的带有焊接接头管材进行检查.通过扫描电镜观察了服役后的管体、焊接接头、焊接热影响区和腐蚀晶界横截面的微观形貌,并结合能谱仪对以上区域进行了元素分析.结果表明:①服役后Incoloy 825合金管材表面发生了晶间腐蚀且局部腐蚀坑内的晶间腐蚀更为严重,但却未发现硫化物腐蚀产物沉积;②焊接热影响区晶粒长大且晶界有析出相,但未发现局部腐蚀;③Incoloy 825合金管材内表面发现的点蚀为酸洗钝化处理时过酸洗造成的:④在服役过程中,Incoloy 825合金管材和焊接接头腐蚀轻微;⑤虽然过酸洗导致了管材内表面的局部腐蚀,但经酸洗钝化处理后的钝化膜则具有较强的耐蚀能力;⑥服役时的高温高压酸性环境不会对已酸洗钝化的Incoloy 825合金管材造成侵蚀,也不会导致局部腐蚀扩展.
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