600 MW超临界锅炉高温过热器T23和T91金属氧化膜热应力分析

以某600 MW超临界锅炉高温过热器为研究对象,分析了氧化膜厚度、生长温度和热膨胀系数等参数对金属管内蒸汽侧氧化膜热应力的影响.基于有限元方法建立了圆管数值计算模型,计算得到不同厚度和不同生长温度下T23和T91金属蒸汽侧氧化膜从生长温度冷却至常温时的热应力变化,并依据热应力的变化特征确定了这2种金属管材蒸汽侧氧化膜易发生脱落的温度范围.结合锅炉出口蒸汽温度与高温过热器指定位置处氧化膜温度的关系,提出用出口蒸汽温度判别氧化膜是否处于易发生脱落的温度范围的方法,给出了该锅炉停炉时的出口蒸汽温度值.结果表明：2种金属管材在冷却过程中低于一定温度时,其氧化膜的应力达到或接近最大应力值,可以依此判断氧化膜是否处于易发生脱落的危险区域.

Thermal Stress Analysis of Oxide Films on T23 and T91 HT Superheater Tubes of 600 MW Supercritical Boilers

Taking the high-temperature （HT） superheater of a 600 MW supercritical boiler as an object of study,the effects of thickness,growth temperature and thermal expansion coefficients of steam-side oxide scale on its thermal stress were analyzed.A numerical calculation model was established for round tubes based on finite element method,with which the thermal stress variation of oxide film on steam side surface of T23 and T91 tubes was calculated during the cooling process from growth temperature to ambient temperature at different thicknesses and growth temperatures,and subsequently the susceptible temperature ranges （STR） in which the steam-side oxide film formed respectively on T23 and T91 tubes is easy to peel off was determined according to variation laws of the thermal stress.By correlating the temperature of boiler outlet steam with the temperature of oxide scale formed on specified location in the HT superheater,a method using the boiler outlet steam temperature to identify whether the oxide scale is within the STR was proposed,and for boiler shut-down processes,the recommended value for boiler outlet steam temperature was also presented.Results show that when the tubes are cooled to be lower than certain temperatures,the stresses in the scale will approach their maximum values,which can therefore be employed to judge whether the temperature of the scale is within the STR.