660MW超临界锅炉屏式过热器管圈长时超温失效特征分析

Long-term over temperature failure characteristics of a tube coil on a 660 MW super-critical boiler platen superheater

结合对超临界锅炉屏式过热器一起长期超温爆管案例的分析,通过力学性能试验、金相检验、扫描电镜、能谱、电子背散射衍射等方式详细分析了爆管所处整个管圈不同位置长期超温运行后的金属特征差异及成因,结果表明：在长期超温条件下,T91钢材质明显老化,强度下降,同样超温运行状态下,TP347HFG耐热钢表现出远优于T91钢的蠕变断裂强度;U型管圈如果发生长时超温爆管现象,出口一侧超温几率更高,爆管位置通常出现在出口端管段上,入口一侧的管子则处于正常的许用温度以内。

Combined with failure analysis of a tube explosion case due to long-term over temperature in a super-critical boiler platen superheater, the variation of metallic characteristics on different locations of the tube coil and their forming causes are discussed in details and analyzed by means of mechanical properties test, metallographic examination, scanning electron microscopy （SEM）, energy dispersive spectrometer （EDS） and electron backscattered diffraction （EBSD）. Results show that under the condition of long term over temperature, T91 steel is aged evidently and its strength decreases, however, the creep rupture strength of TP347HFG steel is much higher in the same condition. If a U-type tube coil explodes due to long-term over temperature, the tube located in the outlet side is usually under over temperature condition so that the explosion probability is relatively higher, while the tube located in the entrance side is under the allowable temperature condition at the same time.