300MW亚临界机组锅炉屏式过热器管爆裂原因分析

Bursting Causes Analysis of Platen Superheater Tube of a 300 MW Sub-critical Unit

某锅炉用T91（10Cr9Mo1VNb）钢屏式过热器管在服役8×10^4h后发生爆裂。通过宏观分析、金相检验、硬度测试、扫描电镜及能谱分析,对其爆裂原因进行了分析。结果表明：由于过热器管长时过热首先产生局部鼓包,弯头处不断变形并达到蠕变断裂强度后产生爆裂,先断裂部位为塑性断裂,其余为脆性断裂;该屏式过热器管爆裂的主要原因是长时过热,导致管道组织发生了严重老化和显著蠕变,而弯头处氧化皮堆积使得蒸汽流量减小是导致管道长时过热的主要原因。

The T91 （10CrgMolVNb） steel platen superheater tube of a boiler burst after 8 × 10^4 n service and the bursting reasons were analyzed by means of macroscopic analysis, metallographic examination, hardness test, and SEM and EDS analysis. The results show that because of longtime overheating, bulge firstly appeared on the brush-fire superheater tube, then the elbow constantly deformed and burst when its stress reached the creep rupture strength. The mechanism of first fracture site was plastic fracture while the mechanism of rest was brittle fracture. The main reason of bursting of the platen superheater tube was longtime overheating, which resulted in serious aging and significant creep of microstructure of the tube. And the longtime overheating was caused by the decrease of steam flow resulting from oxides accumulation at the tube elbow.