某电厂汽轮机一抽汽疏水弯管在服役约4 a(年)后发生泄漏,在弯管两颊出现了两条轴向裂纹,现场调查发现该弯管两端有4道环焊缝及补焊现象.采用宏观形貌观察、化学成分分析、金相分析、扫描电镜与能谱分析等手段对弯管泄漏原因进行了分析.结果表明:该管段内部介质中含有一定量的氯离子,在焊接残余应力及循环热应力的共同作用下弯管发生了应力腐蚀开裂和腐蚀疲劳开裂,最终导致弯管发生泄漏失效.

Cracking and leakage of the extraction steam drain elbow of a steam turbine in a nuclear power plant occurred after four years of service,and an axial crack was found on both sides of the elbow.Field investigation found 4 girth welds and repair welding at two ends of the elbow.The leakage reasons were analyzed by means of macro examination,chemical compositions analysis,metallographic examination and SEM and EDS analysis.The results show that because there was a certain content of chloridion in the pipe medium,stress corrosion cracking and corrosion fatigue cracking happened under the coactions of welding residual stress and thermal cycling stress,which resulted in the leakage of the elbow.