余热发电锅炉过热器管弯头开裂原因分析  

Cracking cause analysis of elbow in superheater tube of a waste heat power generation boiler

作　　者：刘献良 赖云亭[1] 於旻 赵朋飞[1] LIU Xianliang;LAI Yunting;YU Min(不详)

机构地区：[1]苏州热工研究院有限公司,江苏苏州215004

出　　处：《电力科技与环保》2021年第1期57-60,共4页Electric Power Technology and Environmental Protection

基　　金：国家重点研发计划“超期服役承压设备寿命预测及延寿关键技术研究”(2016YFC0801905)。

摘　　要：针对某余热发电锅炉低压过热器受热面管弯头出现大量开裂的情况,对开裂弯头取样进行了外观检查、化学成分分析、硬度测试、金相检验、能谱分析等试验,以分析裂纹形成的原因。结果表明:弯头成型后硬度较高,存在较高的残余应力;裂纹在弯头内壁表面形成,向外壁扩展,具有较多的二次分叉微裂纹,且均为沿晶裂纹,具有碳钢或低合金钢碱脆开裂的典型特征;断口表面存在一定量的Na、P等元素,与锅炉煮炉时所用碱液成分相同,说明煮炉时碱液进入了过热器。综上得出弯头开裂的原因为:锅炉煮炉过程控制不当,导致碱液进入了过热器内部,并在管子内壁表面浓缩,在弯头成型后较高的残余应力和煮炉及运行过程中的热应力、工作载荷应力等共同作用下,最终导致了弯头碱脆开裂。For a large number of cracks in the heating surface tube elbow of the low-pressure superheater of a waste heat power generation boiler,the cracked elbows were sampled for visual inspection,chemical composition analysis,hardness test,metallographic inspection,energy spectrum analysis and other tests to analyze the causes of crack formation.The results show that the hardness of the elbow after forming is higher than normal,which results in higher residual stress of the elbow.Cracks are formed on the inner wall surface of the elbow and expand to the outer wall.The main cracks have more secondary micro-crack branchings,and all of them are intergranular cracks,which have the typical characteristics of alkali embrittlement cracking in carbon steel or low alloy steel.There is a certain amount of Na,P and other elements on the surface of the fracture,which is consistent with the composition of the lye used in the boiler soda boiling,indicating that the lye has entered the superheater during the soda boiling process.In summary,the reason for elbow cracking is that the improper control of soda boiling process caused the lye enter into the superheater and concentrated on the surface of elbow,with the higher residual stress of the elbow,thermal stress during operation,and working load stress,the elbow cracked because of alkali embrittlement finally.

关 键 词：20钢 过热器管 开裂 碱脆 苛性脆化 

分 类 号：TG172.6[金属学及工艺—金属表面处理]