某电厂空气预热器搪瓷涂层失效分析
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摘要
某电厂300 MW机组检修发现空气预热器冷端换热片大面积变形损坏,搪瓷涂层剥落失效。通过对搪瓷涂层的化学成分、涂层厚度、微观组织结构、抗热硫酸腐蚀性能和失效件表面腐蚀产物进行研究。发现空预器冷端蓄热元件单侧涂层厚度约为150μm,主要化学成分为Al、Si、Na、K、Ca、Li、O,沸腾硫酸腐蚀导致的涂层减薄约22μm,涂层内部存在直径约10~120μm的气泡群,其中直径超过80μm的大气泡约占20%,气泡侧壁存在尖角。研究认为搪瓷涂层失效原因主要为大直径气泡减小了搪瓷涂层的有效厚度,使其耐腐蚀防护寿命降低;在设备运行过程中,气泡尖角处将产生应力集中并形成裂纹源,由于交变温度场及应力场的影响,裂纹逐渐扩展,横向扩展导致涂层脱落;纵向扩展至涂层表面导致硫酸溶液渗透到达基材从而导致酸蚀破坏。
Enamel coatings are widely used on the cold end of air pre-heaters to prevent particles erosion and sulfuric acid dew point corrosion. During an overhaul of a 300 MW power plant, it was found that there existed heavy damages and spallation of enamel coating on the cold end plates. Therefore, the chemical composition, thickness, microstructure, resistance to hot sulfuric acid and corrosion products of the enamel coating were examined. Results show that the coating thickness is about 150 μm, its main components are Al, Si, Na, K, Ca, Li and O, and the corrosion depth is about 22 μm. Clusters of bubbles with diameters of 10~120 μm inside the coating could be observed, the diameter of 20% bubbles is above 80 μm. Large bubbles can significantly reduce the effective thickness of the coating and decrease the service life. The sharp corners in the wall of the bubbles can result in stress concentration and become the origin of cracks during operation. The micro-cracks gradually expand under the alternate fields of temperature and stress. When it expands transversely, the coating may be suffered from spallation.While it expands longitudinally to penetrate the coatings, so that the substrate will easy be suffered from sulfuric acid dew point corrosion.
Enamel coatings are widely used on the cold end of air pre-heaters to prevent particles erosion and sulfuric acid dew point corrosion. During an overhaul of a 300 MW power plant, it was found that there existed heavy damages and spallation of enamel coating on the cold end plates. Therefore, the chemical composition, thickness, microstructure, resistance to hot sulfuric acid and corrosion products of the enamel coating were examined. Results show that the coating thickness is about 150 μm, its main components are Al, Si, Na, K, Ca, Li and O, and the corrosion depth is about 22 μm. Clusters of bubbles with diameters of 10~120 μm inside the coating could be observed, the diameter of 20% bubbles is above 80 μm. Large bubbles can significantly reduce the effective thickness of the coating and decrease the service life. The sharp corners in the wall of the bubbles can result in stress concentration and become the origin of cracks during operation. The micro-cracks gradually expand under the alternate fields of temperature and stress. When it expands transversely, the coating may be suffered from spallation.While it expands longitudinally to penetrate the coatings, so that the substrate will easy be suffered from sulfuric acid dew point corrosion.
引文
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[6] Du H J. Enamel tube air-preheater resistant to dew point sulfuric acid corrosion[J]. Corros. Prot. Petrochem. Ind., 2007, 24(4):38(杜洪建.耐硫酸露点腐蚀的搪瓷空气预热器[J].石油化工腐蚀与防护, 2007, 24(4):38)
[7] Xu W H. Corrosion resistant retrofits of the air preheaters of gas boilers[J]. Chem. Eng. Mach., 2009, 36:386(徐文豪.燃气锅炉空气预热器的防腐改造[J].化工机械, 2009,36:386)
[8] He L B, Zuo J, Lin B C, et al. Corrosion-resistance evaluation of materials of heat pipe for system of wet desulfurization of flue Gas[J]. Corros. Sci. Prot. Technol., 2003, 15:111(何立波,左军,林伯川,等.烟气湿法脱硫系统中热管的耐腐蚀实验研究[J].腐蚀科学与防护技术, 2003, 15:111)
[9] Ouyang Q, Zhong J Q. Enamel coating defects and quality test of enamel products[J]. China Enam., 1998, 19(6):17(欧阳秋,钟江泉.搪瓷制品瓷层缺陷及质量检验[J].中国搪瓷,1998, 19(6):17)
[10] Wen R C, Lu G W. Air-bubble configuration-the peculiar configuration of enamel coatings[J]. Class Enam., 1989, 17(6):29(闻瑞昌,卢桂文.气泡结构——搪瓷层的独特结构[J].玻璃与搪瓷, 1989, 17(6):29)
[11] Gou W B. The structure and formation concept of the enamel layer[J]. Bull. Chin. Ceram. Soc., 1981,(3):40(芶文彬.搪瓷层的结构与形成概念[J].硅酸盐通报, 1981,(3):40)
[12] Jia S G, Wang D C, Ding H, et al. Research on corrosion of air preheater of biomass fuel-directly fired boiler[J]. Huadian Technol.,2014, 36(8):70(贾少刚,王定才,丁恒等.生物质直燃锅炉空气预热器腐蚀研究[J].华电技术, 2014, 36(8):70)
[13] Pang Y. Analysis and treatment of corrosion in low temperature heat exchange section of air preheater[J]. Sci. Technol. Inf., 2012,(12):103(逄燕.空气预热器低温换热段腐蚀问题原因分析及处理措施[J].科技资讯, 2012,(12):103)
[14] Shan Z X. Model on constant speed wind turbine based on common asynchronous generator and its interconnection with power grid[J]. Electr. Power Technol., 2010, 19(3):33(单志栩.搪瓷传热元件在600MWe机组空预器改造上的实践[J].电力技术, 2010, 19(3):33)
[15] Mi F Y, Zhu S L. Long-term high temperature oxidation and hot corrosion behavior of an enamel coating onγ-TiAl intermetallics at 700℃[J]. Corros. Sci. Prot. Technol., 2015, 27:254(米丰毅,朱圣龙.搪瓷涂层700℃长期抗高温氧化和热腐蚀行为研究[J].腐蚀科学与防护技术, 2015, 27:254)
[16] Huang W L. Enamel coating with a strong alkali calcium boron silicate glass ground coating[J]. Class Enam., 1973, 1(2):42(黄维琳.以强碱钙铝硼硅酸盐玻璃为底釉的搪瓷涂层[J].玻璃与搪瓷, 1973, 1(2):42)
[2] Liu J Y, Liu X, Sun W. Application of enamel on air preheaters[J].Petrochem. Corros. Prot., 2000, 17:22(刘建业,刘馨,孙伟.搪瓷在空气预热器上的应用[J].耐蚀材料,2000, 17:22)
[3] Ma C Y. Application of enamel elements in air preheater of remolding unit[J]. Heilongjiang Sci. Technol. Inf., 2015,(19):110(马春雨.搪瓷元件在脱销改造机组空气预热器的应用[J].黑龙江科技信息, 2015,(19):110)
[4] Bai X L, Zhao J B. Reformation of cool terminal heat exchange elements of air heater using enameled elements[J]. Huadian Technol.,2010, 32(6):57(白学利,赵俊斌.空气预热器冷端换热元件的搪瓷改造[J].华电技术, 2010, 32(6):57)
[5] Xu Y L, Xu C J, Zhang Y Y, et al. Reconstruction scheme for preventing the low temperature corrosion of air preheater[J]. Beijing Energy Conserv., 2000,(6):42(许彦雷,徐传健,张永义等.防止空气预热器低温腐蚀的改造方案[J].节能与环保, 2000,(6):42)
[6] Du H J. Enamel tube air-preheater resistant to dew point sulfuric acid corrosion[J]. Corros. Prot. Petrochem. Ind., 2007, 24(4):38(杜洪建.耐硫酸露点腐蚀的搪瓷空气预热器[J].石油化工腐蚀与防护, 2007, 24(4):38)
[7] Xu W H. Corrosion resistant retrofits of the air preheaters of gas boilers[J]. Chem. Eng. Mach., 2009, 36:386(徐文豪.燃气锅炉空气预热器的防腐改造[J].化工机械, 2009,36:386)
[8] He L B, Zuo J, Lin B C, et al. Corrosion-resistance evaluation of materials of heat pipe for system of wet desulfurization of flue Gas[J]. Corros. Sci. Prot. Technol., 2003, 15:111(何立波,左军,林伯川,等.烟气湿法脱硫系统中热管的耐腐蚀实验研究[J].腐蚀科学与防护技术, 2003, 15:111)
[9] Ouyang Q, Zhong J Q. Enamel coating defects and quality test of enamel products[J]. China Enam., 1998, 19(6):17(欧阳秋,钟江泉.搪瓷制品瓷层缺陷及质量检验[J].中国搪瓷,1998, 19(6):17)
[10] Wen R C, Lu G W. Air-bubble configuration-the peculiar configuration of enamel coatings[J]. Class Enam., 1989, 17(6):29(闻瑞昌,卢桂文.气泡结构——搪瓷层的独特结构[J].玻璃与搪瓷, 1989, 17(6):29)
[11] Gou W B. The structure and formation concept of the enamel layer[J]. Bull. Chin. Ceram. Soc., 1981,(3):40(芶文彬.搪瓷层的结构与形成概念[J].硅酸盐通报, 1981,(3):40)
[12] Jia S G, Wang D C, Ding H, et al. Research on corrosion of air preheater of biomass fuel-directly fired boiler[J]. Huadian Technol.,2014, 36(8):70(贾少刚,王定才,丁恒等.生物质直燃锅炉空气预热器腐蚀研究[J].华电技术, 2014, 36(8):70)
[13] Pang Y. Analysis and treatment of corrosion in low temperature heat exchange section of air preheater[J]. Sci. Technol. Inf., 2012,(12):103(逄燕.空气预热器低温换热段腐蚀问题原因分析及处理措施[J].科技资讯, 2012,(12):103)
[14] Shan Z X. Model on constant speed wind turbine based on common asynchronous generator and its interconnection with power grid[J]. Electr. Power Technol., 2010, 19(3):33(单志栩.搪瓷传热元件在600MWe机组空预器改造上的实践[J].电力技术, 2010, 19(3):33)
[15] Mi F Y, Zhu S L. Long-term high temperature oxidation and hot corrosion behavior of an enamel coating onγ-TiAl intermetallics at 700℃[J]. Corros. Sci. Prot. Technol., 2015, 27:254(米丰毅,朱圣龙.搪瓷涂层700℃长期抗高温氧化和热腐蚀行为研究[J].腐蚀科学与防护技术, 2015, 27:254)
[16] Huang W L. Enamel coating with a strong alkali calcium boron silicate glass ground coating[J]. Class Enam., 1973, 1(2):42(黄维琳.以强碱钙铝硼硅酸盐玻璃为底釉的搪瓷涂层[J].玻璃与搪瓷, 1973, 1(2):42)
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