Investigation of the Resistance to Localized Corrosion Associated with Microstructure of Tube-to-Tube Sheet Welds of UNS S32050 Super Austenitic Stainless Steel for Seawater Cooled Condenser

Abstract

The behaviors of localized corrosion associated with microstructure of tube-to-tube sheet welds of UNS S32050 super austenitic stainless steel for seawater cooled condenser were investigated in highly concentrated chloride environments. In the interdendritic region, Cr and Mo as -stabilizers were enriched and N as the -stabilizer was depleted whereas in the dendrite core, Cr and Mo were depleted and N was enriched. Based on the PREN IR and PREN DC values, the localized corrosion was selectively initiated at the dendrite core (DC) because the PREN value of the dendrite core was much smaller than that of the interdendritic region (IR). It was found that the resistance to localized corrosion of the UNS S32050 SASS tube-to-tube sheet welds at least as good as that of a UNS S31254 SASS base metal with PREN 47 in highly acidified chloride environments.

Aging of passive film on UNS N08031 in a Green-Death solution

“…It is reported that the thickness of the passive oxide film formed on UNS S32050 that contains less than 4 and 10 wt-% Cr and Ni, respectively, than UNS N08031 is ca. 2 nm in 25 wt-% NaCl solution at 70°C [23]. It has been reported that an increase in the Cr content in FeCrNi alloy makes a film thicker [24] while alloying elemental Ni does not affect the formation or thickness of a film [25].…”

Effect of Acidic and Alkaline Solutions on Electrochemical Corrosion of Zircaloy-2

“…The breackdown potential of passivity (E bd ) was observed and the passive region decreases with an increase of sodium and potassium concentration. The loops in these curves are characterized by negative hysteresis indicates the passive film formed on the surface of the specimen after breakdown characterized by selfhealing [27,25].The resistance to corrosion of an alloy increases with an increase in the passive region (∆E p ) [28]…”