超超临界锅炉垂直管圈水冷壁焊缝交错区域温度场建模及热应力模拟

Temperature Field Modeling and Thermal Stress Simulation in Vertical Water-wall Weld Staggered Region of the Ultra-supercritical Boiler

以某660 MW超超临界锅炉为对象,构建垂直管圈水冷壁焊缝交错区域温度场模型,研究热应力分布对裂纹的影响。结果表明:焊缝交错区域管环焊缝向火侧顶点的温度高于直管段管壁向火侧顶点温度,发生超温时比直管段管壁向火侧更容易开裂;水冷壁管最大轴向拉应力位于焊缝交错区域管环焊缝焊趾向火侧顶点附近,在变负荷运行工况下易导致交变热应力,产生沿管环焊缝焊趾延伸的横向裂纹;焊缝交错区域应力集中处的等效应力大于直管段对应处,背火侧管环焊缝焊趾与鳍片角焊缝交接处等效应力最大,超过对应的高温屈服强度,材料在交变热应力作用下会诱发裂纹,裂纹沿管环焊缝焊趾向背火侧管壁延伸。

Taking a 660 MW ultra-supercritical boiler as research object,the temperature field model in vertical water-wall weld staggered region was constructed to study the effects of thermal stress on cracks.Results show that the temperature at the fire-facing side of the tube girth weld in the weld staggered region is higher than that of the straight tube wall,and it is easier to crack than that of the straight tube wall in case of overtemperature.The maximum axial tensile stress is located near the fire-facing side at the weld toe of the tube girth weld in the weld staggered region.It is more likely to cause alternating thermal stress under variable load operating conditions and transverse cracks would be formed extending along the weld toe of the tube girth weld.The equivalent stress at the stress concentration position in the weld staggered region is greater than that at the corresponding position of the straight tube section.The equivalent stress at the junction between the weld toe of the tube girth weld and the fin fillet weld on the back fire side is the largest,which exceeds the corresponding high-temperature yield strength,and cracks would be induced by alternating thermal stress,and the cracks extend along the weld toe of the tube girth weld to the tube wall on the back fire side.