火力发电厂锅炉屏式过热器弯管泄漏失效原因分析及预防措施

Analysis and Prevention of Platen Superheater Elbow Leakage of Supercritical Boiler in a Coal-fired Power Plant

某600 MW发电机组锅炉屏式过热器发生漏泄,造成机组非正常停机。通过现场检查、宏观、微观、测厚及化学成分分析,结合金相组织以及硬度分析,综合判断了管材失效的原因。结果表明,屏式过热器最内圈弯管不合理的结构及长周期的交变载荷作用,使弯管外壁内弧面产生横向疲劳裂纹,并向内壁扩展。高温高压蒸汽在该位置发生初始泄漏,连锁吹损其它管段,最终导致事故的发生;内壁表面加工划痕沟槽等原始缺陷是过热器弯管中性面的裂纹源,在爆裂及蒸汽泄漏过程的影响下向外壁扩展,形成贯穿性裂口。为防止类似事故再次发生,在检修、监督、设计及制造等方面均提出了相应的预防措施。

Leakage of platen superheater in a 600 MW Power Unit resulted an anormal shutdown.The causes of superheater leaking were analyzed and studied through on-site inspection,macroscopic,microscopic,thickness measurement,chemical composition analysis,combined with metallographic structure analysis and hardness analysis.The results show that the transverse fatigue cracks occur on the inner arc surface of the outer wall of the tube and extend to the inner wall due to the unreasonable structure of the tube and the long period of alternating load.The initial leakage of high temperature and high pressure steam in this position leads to the chain blowing of other pipe sections,which ultimately leads to the occurrence of the unit shut down abnormally;The original defects,such as scratches and grooves,are the source of cracks in the neutral surface of the superheater elbow,which expand to the outer wall and form penetrating cracks under the influence of the process of burst and steam leakage.In order to prevent similar accidents from happening again,corresponding preventive measures are put forward in maintenance,supervision,design and manufacturing.