600 MW超临界锅炉末级过热器失效原因探析

某电厂3号超临界锅炉投产后运行不到500 h便发生4次末级过热器爆漏事故,其部位多发生在外数第2、3、4、20内圈管,特征为管屏下部内弯头横向裂纹.过热器爆漏的主要原因为末级过热器SA-213TP347在弯管后未经固溶处理,致使末级过热器内弯处管材存在晶间腐蚀和硬度超标;同时末级过热器由于其管系设计布置不合理,运行中与烟气紊流发生共振,致使末级过热器内弯头在极短的时间内快速疲劳失效.通过采用增加末级过热器固定管夹,改变其固有频率,将末级过热器下部弯头更换为经固溶处理的弯管等措施后,锅炉再未发生类似的失效损坏.

Analysis of Final Stage Superheater Failure of 600 MW Supercritical Pressure Boiler

After No.3 supercritical boiler in a certain power plant operated for less than 500 h since its commissioning,bursting and leakage failures occurred four times in the final stage superheater; The bursts mostly were located on the inner tracks of tubes rank 2,3,4and 20 from outside,featuring transvers cracks on the internal elbows of tube platen's underpart. According to the analysis,the main causes of superheater bursting and leakage were,solution treatment were not carried out after tube bending,and the design of tube ararngement was inappropriate,resulting in the intercrystalline corrosion and hardness beyond standard in the material of inner elbows,and the resonance with flue gas twrbulence,leading to fatigue failure of inner elbows rapidly. By adding tube fixing clamps on the final stage superheater to change its natural frequency and by changing the underpart elbows to those having undergone solution treatment,such bursts never occur up to now.