蒸汽发生器炉管壁减薄机理

从腐蚀理论和影响因素来解释了“蒸汽发生器炉管失效分析”一文中所揭示的现象,蒸汽发生器炉管减薄主要源于内表面腐蚀,炉管径向截面出现裂纹和次生裂纹,腐蚀表面有冲蚀和气蚀痕迹。介绍了蒸汽发生器炉管壁减薄机理,炉管壁在高温高压的工况下,金属与水汽接触产生汽水腐蚀,形成以氧化铁为主的腐蚀产物。炉管内液体在流动过程中地被加热,产生大量的蒸汽泡,蒸汽泡溃灭过程中造成氧化膜甚至母体金属破坏。与此同时,应力和活性阴离子对氧化膜的破坏造成孔蚀;氧的存在加剧了腐蚀作用。气蚀作用能使脱落的固体颗粒在水汽中形成固液汽三相流冲蚀作用,使材料被除去,母体金属与介质直接接触,周而复始的连续作用使管壁减薄。通过论述,以期对炉管减薄有更清晰的认识,从而对蒸汽发生器的使用起到一定的指导作用。

PRINCIPLE OF THE DECREASING WALL THICKNESS OF BOILER TUBE OF VAPOR GENERATOR

On the base of the corrosive theory and the effected factors, this paper presented the phenomena shown in the article” The Failure Analyses of the Boiler Tube of vapor Generator”. The decreasing wall thickness of boiler tube of vapor generator mainly resulted in the inner wall corrosion of the tube, and then the radius cross section of the boiler tube produced fracture and sub-fracture, and the corrosive surface of the tube produced some erosion and cavitation. The paper introduced the principle of the decreasing wall thickness of boiler tube of vapor generator. Under the high temperature and high pressure, the metal in contact with the vapor-water formed the vapor-water corrosion, the tube wall is corroded and mainly produced iron oxide. The liquid heated in the tube produces a lot of bubbles when flowing, the oxidic film and metal base will be damaged when the bubbles break, .At the same time, stress and active anion will destroy the oxidic film. Corrosion is more serious duo to the solid particles and oxygen in the liquid. By the discussion in this paper, the corrosion and the decreasing wall thickness of boiler tube are understood clearly, and it provides a guide for the vapor generator application.