Failure analysis of austenitic stainless steel tubes in a gas fired steam heater

摘要: Abstract Carryover of caustic soda (NaOH) in the steam path caused catastrophic failure superheater 304H stainless steel tubes a gas fired heater and led to an unexpected shutdown after just 5 months continuous service following start production. The cause was studied, with focus on effect embrittlement stress corrosion cracking (SCC). cracks were examined at seam weld, heat affected zone (HAZ), U-bend areas. Hardness measured for base metal, HAZ, weld microstructures using optical microscopy scanning electron (SEM). Crack initiation is attributed gouging precipitated carbide HAZ also formation sigma phase as shown by energy dispersive X-ray (EDX) analysis. In addition, propagated because residual stresses hammering. Finally, characteristic feature fracture illustrated SEM fractography, consists mostly intergranular SCC some quasi-cleavage transgranular.