670MW超临界锅炉TP347H再热器管失效分析

Failure Analysis of TP347H Tubes from Reheater in a 670MW Supercritical Boiler

通过宏观检查、力学性能试验、金相检验、微观形貌观察及化学成分分析等方法,对某670MW超临界锅炉TP347H末级再热器爆管进行了失效分析.结果 表明:管子弯头未固溶处理导致材料存在较高的残余应力和位错密度,残余应力和位错在奥氏体耐热钢敏化温度区间会加速晶界处富Cr碳化物M23C6的析出,造成晶界贫铬,严重降低了晶界的耐腐蚀性能.再热器管弯头在应力和腐蚀介质的交互作用下产生了应力腐蚀裂纹,长时间运行导致裂纹扩展,从而导致爆管.为避免类似事故,提出了几点预防措施.

The burst failure reason of TP347H final reheater tube in a 670MW supercritical boiler was studied by macroscopic inspection,mechanical properties test,metallographic examination,morphology observation and chemical composition analysis.The results show that the higher residual stress and dislocation density due to absence of solution treatment for elbow of TP347H final reheater tube would acelerate the precipitation of Cr-rich M23C6 along the grain boundaries of austenitic heat resistant steel in the sensitization temperature range.The formation of chromium-deleted zones near the grain boundaries seriously reduced the corrosion resistance of the grain boundaries.Under the interaction of stress and corrosive medium,the stress corrosion crack initiated in the elbow of the reheater tube and propagated after long-term operation,which eventually leads to tube burst.In order to avoid similar accidents,several preventive measures are proposed in this paper.