汽轮机高压内缸紧固螺栓高温断裂失效原因分析

Cause Analysis on High Temperature Fracture of Fastening Bolts of High Pressure Inner Cylinder of Steam Turbine

兰溪发电厂汽轮机高、中压内缸螺栓采用镍基超高温合金作为紧固件材料,螺栓在机组高温运行时发生了断裂。对断裂失效的Nimonic 80A螺栓进行了宏观检查、超声检测、光谱分析、金相分析以及力学性能分析,查阅Nimonic 80A螺栓的材料特性,分析后得出:螺栓断裂可能与该材料在500℃以下产生负蠕变、螺栓晶粒大小不均匀并呈带状组织以及应力腐蚀等因素有关。

Nickel based superalloys are used as fastening bolts for high and medium pressure inner cylinder of steam turbine in Lanxi power plant. The bolts fractured in high temperature operation of units. Macroscopic examination, ultrasonic detection, spectrum analysis, metallographic analysis and mechanical performance analysis on the fractured Nimonic 80 A bolts were conducted. By referring to material property of Nimonic80 A bolts, the paper concludes that the bolt fracture results from negative creep under 500 ℃, uneven crystal grain of bolt and the banded structure as well as stress corrosion.