某超超临界机组末级过热器泄漏原因分析

Analysis on the Leakage of Final Superheater in a Ultra-Supercritical Unit

针对发生泄漏的末级过热器管进行失效分析。通过宏观检查、金相检验、硬度检验及扫描电镜分析,对管子泄漏原因进行综合评判。结果表明:管子在制造过程中成型工艺控制不当,导致管内壁存在大量轴向分布的线性缺陷,在服役过程中缺陷向管子内部扩展,造成管子有效壁厚减小;服役过程中随着管子组织的老化,性能逐渐劣化,导致管子承压能力下降,最终某处裂纹失稳扩展导致泄漏,引起多处裂纹扩展,形成天窗状爆口。

Failure analysis on the final superheater tube that has experienced leakage is conducted.A comprehensive evaluation of the cause of tube leakage is conducted through macroscopic examination,metallographic examination,hardness test,and SEM analysis.The results indicate that:The leakage of the final superheater tube was caused by improper control of the forming process of the tube during the manufacturing process,resulting in a large number of axially distributed linear defects existed on the inner wall.The defect spreads to the inside of the tube during service,resulting in a great reduction in the effective wall thickness of the tube.With the aging of the pipe organization,the performance is gradually deteriorated,which leads to a decrease in the pressure-bearing capacity of the tube.Finally,the unstable expansion of cracks leads to leakage,causing multiple cracks to expand,forming a skylight-shaped explosion.