电厂用锅炉水冷壁辐射过热器管弯头开裂原因分析

Analysis of failure in elbow of radiation superheater of 500MW boiler in a power plant

研究了某电厂500MW锅炉水冷壁辐过管弯头在服役条件下受力特征、显微组织变化和变形规律,探讨了其开裂原因.研究认为弯头管子表面裂纹属于热疲劳裂纹.炉管在热循环过程中的变形约束是引起热疲劳开裂的主要原因.在蠕变可以进行的温度下,弯头管子受弯矩作用,“中性轴”上的横向应力升高,引起管子蠕变变形、截面椭圆化,而蠕变变形和再结晶过程等对热疲劳损伤起到促进作用.还应用“破裂前渗漏”准则评定了弯头管子的安全性,认为辐射过热器管设计符合破裂前渗漏准则,并有相当大的安全欲度.

The stress analysis, microstructure change and deformation law of the elbow of the radiation superheater of a 500 MW power boiler were studied and the reason of its failure was discussed. The results indicate that the surface cracking on the elbow is ascribed to thermal fatigue damage induced by mechanical constraint to thermal strain in processes of the thermal cycles. The transverse bending stress at the neutral axis of the elbow is higher than neighboring pipe under applied bend moment. This higher stress causes creep deformation and ovalling of the bend pipe section, and the process of creep and recrystallization promotes thermal fatigue damage. A safety evaluation of the elbow shows that the design conforms to leak-before-break criterion and a large margin of safety is allowable.