某1000MW超超临界机组汽轮机IN783螺栓断裂失效分析

Failure Analysis of IN783 Alloy Bolt Used on 1000MW Ultra Supercritical Steam Turbine

某电厂1000MW超超临界机组汽轮机再热主汽阀、再热调节阀阀盖与阀体紧固螺栓在运行过程中发生了失效现象。通过化学成分分析、宏观、微观组织分析及相应的力学性能试验等分析检测可知,螺栓材料在长期高温服役后,基体和β相中析出了较多的其它物相组织,造成材料的脆化及晶界弱化,降低了螺栓的塑韧性。检修时旧的安装工艺使螺栓处于较大的应力状态,加上高温运行时蒸汽推力的共同作用,螺纹、加工缺陷处的应力集中无法通过塑性变形释放,导致这些部位裂纹萌生并快速扩展,最终引发螺栓的脆性断裂。

IN783 alloy fastening bolt used on steam turbine for fastening valve body and bonnet are broken during service. To clarify this phenomenon, chemical component, macrostructure and microstructure, hardness and tensile strength are conducted and analyzed. It is found that new phases are formed in matrix and β phase of the bolt after a long high temperature service, which increase the brittleness and weaken the grain boundary, resulting in a reduction of its ductility and toughness. What's more, a high stress induced in the bolt after the old refasten process, and stress concentration generating at surface defects can't be released by plastic deformation along with steam impetus at high temperature, causing a crack initiation and then a fast propagation and ultimately a brittle fracture.