某电厂300 MW机组锅炉的SA299材质汽包中部距下降管400~500 mm处出现了一些裂纹,为分析锅炉启停过程汽包的应力变化,采用三维有限元分析方法,运用ALGOR软件对SA299材质的汽包在启停过程热应力和总应力的分布和变化进行了计算.结果表明:在启动过程中水位线处的热应力最大,裂纹处的热应力幅在80 MPa以内,裂纹处的热应力变化与水线处热应力变化趋势基本一致,最大热应力区域接近裂纹产生区域;启停过程中危险点处总应力最大,其应力幅为350 MPa,整个启停过程中,裂纹处的总应力不大,水位线及以下的内壁区域应力比上部和外壁更大;热应力是汽包裂纹产生的诱因之一. Some cracks appeared in the middle of the SA299 material drum of 300 MW unit boiler at a distance of 400-500 mm from the descending pipe. To analyze the stress changes of the steam drum during the start-stop process of the boiler, three-dimensional finite element analysis method was used to analyze the SA299 material The results show that the thermal stress at the water level is the highest during the start-up process, the thermal stress at the crack is within 80 MPa, the heat at the crack The change of stress is consistent with that of thermal stress at the waterline, and the maximum thermal stress is close to the crack initiation area. The total stress at the dangerous point during start-stop is the largest, with a stress of 350 MPa. During the entire process of start-stop, The stress is not large, and the stress in the inner wall region below the water level line is greater than that in the upper part and the outer wall. Thermal stress is one of the causes of the crack in the drum.