超临界锅炉试运行期间屏式过热器爆管原因分析

Analysis on reason of tube cracking of platen superheater during commissioning of supercritical boiler

某电厂超临界W火焰锅炉屏式过热器在试运行期间多次发生爆管事故,对原始管样、爆管管样及氧化皮状异物进行宏观检查、化学成分分析、拉伸性能试验、金相分析、扫描电镜及能谱分析等,结合停炉后内窥镜检查结果,查明爆管的主要原因是大量的原生态或次生态氧化皮状异物脱落堵塞屏式过热器入口集箱节流孔或管子,导致管子介质流量减小,使蒸汽对管子的冷却作用降低,局部处于超温状态,高温蠕变强度降低。

In commissioning process of the platen superheater of supercritical W-shape flame boiler in a power plant,the tube cracking accident occurred repeatedly.The original tube sample,the cracked tube sample and substances similar to oxide skin were inspected by several methods,which include the macroscopic inspection,the chemical composition analysis,the tensile test,the metallographic analysis,the scanning electron microscope and the energy spectrum analysis.Combining with inspection result obtained by endoscope after the boiler shutdown,it was found that the main reason of pipe cracking is that a mass of original or subsequent oxide skin fell off and blocked the throttle orifices and pipe of the header in inlet of the platen superheater,which causes that the medium flow in the pipe reduced,the cooling effect of steam for the pipe became lower;and the local parts of pipe was over temperature,and its high-temperature creep strength decreased.