Failure Analysis of ZG40Ni35Cr25Nb Furnace Tube

Tubes for hydrogen generation furnace were burst and fired after operation for less than 40 000 in a petrochemical company.After macroscopical examination,surface inspection,machanical test,energy spectrum analysis,metallography analysis,electron microscopy inspection,X-ray analysis and stress analysis,it could be concluded that because of the excessive carbides at grain boundaries and the existence of loose cavities,the toughness was weakened,many microcracks were generated,additionally the existence of Na+,Cl-,K+ in the heat preservation material outside of the tubes,stress corrosion cracking occured between the outlet nozzle and the bottom support where rather high stress existed.The leak and fire occured in No.58 tube firstly,other tubes were damaged because of roasting in the exterior for short time,and then bulged and cracked at last.This was main reason of the breakage.Some preventive measures were suggested.