超超临界锅炉屏式过热器爆管原因研究

Research on causes of tube bursting of panel superheater in ultra supercritical boiler

基于探究某电厂T92钢屏式过热器管发生爆管原因的目的,采用宏观检验、化学成分分析、力学性能测试、金相检验等方法对失效管段取样进行试验。试验结果表明,管子化学成分符合ASME SA-213制造标准要求;爆口区域管子金相组织为铁素体+碳化物,马氏体板条位向已严重分散,呈显著老化状态;离爆口稍远的区域金相组织为正常的回火板条马氏体形态,组织老化较爆口位置轻微的多。结合爆口部位在安装过程中有热矫正过程,认为爆口位置金相组织老化与安装过程中的热矫正有关。在此基础上,采用Larson-Miller参数法对管子的使用寿命进行了估算,得出当安全系数为1.2时,使用寿命仅为11.6万h,该规格的管子在目前的运行参数下使用寿命相对较短。综合上述分析,管子化学成分符合ASME SA-213制造标准要求,可排除材质错用的情况;管子安装过程中存在热矫正工艺不当的问题,导致爆口局部区域的显微组织形成了铁素体+碳化物的非正常组织,组织状态恶化,力学性能及持久强度显著下降,经长期服役后,导致了上述局部薄弱区域发生开裂爆管;此外,管子初始设计壁厚偏薄在一定程度上也促进了该管段的过早失效。提出了对屏过联箱密封结构进行改造、加装壁温测点、根据最新技术标准对管子进行重新设计、对锅炉可靠性进行评估等防范措施,对避免同类问题再次发生具有参考意义。

Macro inspection,chemical composition analysis,mechanical performance test and metallographic inspection were carried out of a T92 plate super-heater tube of a power plant.The results show that the chemical composition of the tube meets the requirements of ASME SA-213 standard.The metallographic structure of the tube at the burst area is ferrite and carbide.The orientation of martensitic lath has severely been dispersed which means a significant aging state.The metallographic structure of the area slightly away from the edge is normal morphology which is tempered martensite and the degree of aging is much slighter than that of edge.Combining with the flame-correction in the installation process of the burst area,it is believed that the aging of the metallographic structure of the blast edge is related to it.On the basis,Larson-Miller parameter method is used to estimate the service life of the tube,and the results show that the service life of the tube is relatively short.When the safety factor is 1.2,the calculated service life is only 116,000 hours.It is concluded that the chemical composition of the tube meets the requirements of ASME SA-213 manufacturing standard,which can eliminate the misuse of the tube material.During the installation of the tube,there was a problem of improper heat correction technology,which led to the formation of an abnormal structure of ferrite+carbide in the microstructure of the local area of the blast hole.The state of the structure deteriorated,and the mechanical properties and endurance strength decreased significantly.After long-term service,Resulting in the cracking and bursting of the above-mentioned local weak area.Also,the initial design wall thickness of the pipe is too thin to a certain extent,which also promotes the premature failure of the pipe section.It provides measures such as reforming the sealing structure of the shielding header,installing wall temperature measurement points,redesigning the tubes according to the latest technical standards,and evaluating the reliability of the boiler,which are of reference significance for avoiding the recurrence of the same type of problems.