135 MW锅炉屏式过热器12Cr2MoWVTiB钢爆管失效分析

Failure analysis of bursting 12Cr2MoWVTiB steel pipe of platen superheater for 135 MW boiler

采用化学成分分析、力学性能测试和组织分析等方法,对屏式过热器12Cr2MoWVTiB钢爆管进行了失效研究。结果表明,爆口处化学成分无明显异常,硬度比正常处低约25 HV0.1,显微组织出现明显软化。分析认为,管子长期在超温条件下服役,组织老化导致材料力学性能下降;由于屏过穿排定位管和外圈竖直管相互磨损发生泄漏,后段管子内介质流量减小,壁温迅速升高,短时过热在高温下组织快速软化,造成管子切向应力超过材料强度而发生瞬时超温爆管。

The failure of the platen superheater 12Cr2MoWVTiB steel bursting pipe from a power plant were studied by chemical composition analysis, mechanical properties test and microstructure analysis etc.The results show that chemical composition of the explosion position is normal, but the hardness is about 25 HV0.1 lower than the other area and microstructure is apparently softened.Analysis indicates that microstructure becomes outworn and mechanical properties drop due to long-time over-temperature condition; because of wear leakage between the row positioning tube and the outer vertical tube,the medium flow of the rear tube decreases, and temperature of the tube wall raises rapidly,so the microstructure is quickly softened at the high temperature causing the pipe'tangential stress exceeding the strength of the material itself which leading to pipe bursting in the condition of over-temperature instantaneously.