AVT水工况条件下水冷壁管形成氧化膜的特性研究

Study of the Formation Characteristics of Oxide Film on Waterwall Tubes Under the AVT(All Volatilization Treatment) Water Condition

利用电化学方法、XRD、SEM/EDS等测试手段,研究了600 MW水冷壁管在还原性全挥发处理AVT(R)和弱氧化性全挥发处理AVT(O)两种水工况300℃条件下,氧化18h所形成的氧化膜的形貌、结构,并分析了氧化膜成膜机理,其结果为减少金属在实际运行中的高温腐蚀有指导作用。研究表明:AVT(R)条件下生成的氧化膜分为两层,内层是接触金属基体向内生长的Fe3O4的内伸层,外层是Fe3O4,均匀致密,呈黑色,完全覆盖于金属表面;AVT(O)条件下形成的氧化膜分为3层,氧化膜的内层,即Fe3O4的内伸层,中间层是致密的Fe3O4层,完全覆盖于试样的表层,Fe3O4层上还生长着大颗粒晶体状的氧化物Fe2O3,并形成了氧化膜的外层。

By using electrochemical,XRD,SEM/EDAX etc.testing methods,studied were the morphology and structure of the oxide film on the waterwall tubes of a 600 MW boiler formed in the process of oxidation after 18 hours at 300 ℃ under both AVT(all-volatile treatment)(R) and AVT(O) water condition with the mechanism for forming such oxide film being analyzed.The research findings can offer guidance for reducing the high temperature corrosion of metals in actual operations.It has been found that the oxide film formed under the AVT(R) condition can be divided into two layers.The inner layer represents an inner extension layer of Fe3O4,which grows inwards by contacting with the metal body and the outer layer represents a uniform and compact layer,being in black color and wholly overlaid on the metal surface.However,the oxide film formed under the AVT(O) water condition can be divided into three layers,i.e.an inner layer of the oxide film(inner extension layer of Fe3O4),an intermediate compact layer of Fe3O4,which covers the whole surface layer of the specimen and on which oxide Fe2O3 also grows as large crystal particles,thus,an outer layer is formed.