The Effects of Weld Metallurgy and Passivation Treatment on the Corrosion of Austenitic Stainless Steel Weldment in Urea Service

摘要

Several corrosion damages of 304 stainless steel weldment in SelectiveNon-Catalytic Reaction (SNCR) process have been reported. In thepresent study, the effects of different filler metals and passivationtreatment on the weldments (304 base welded with ER308, 316, 310,2209 and 316L UG fillers) were studied to set-up counter-measuresbased on weld-base metal galvanic test, anodic polarization test andmicrostructure analysis etc.Corrosion was localized at the weld (and/or HAZ) and galvanic currentflowed from the weld to the base metal. This means that weld acted asthe anode and base metal acted as the cathode. Weld metals have morenoble chemical composition compared to the base metal; however, theyshowed poor corrosion characteristics than the base metal due to theirnon-uniform microstructure, more delta-ferrite and poor passive filmproperties. Passivation using 30% HNO_3 enabled weld surface to formprotective Cr_2O_3 film and reduced galvanic corrosion current to almostnegligible levels.