Effects of shielding gases on the microstructure and localized corrosion of tube-to-tube sheet welds of super austenitic stainless steel for seawater cooled condenser

The effects of shielding gas on the microstructure and localized corrosion of tube-to-tube sheet welds of SR-50A super austenitic stainless steel for seawater cooled condense were investigated in highly concentrated chloride environments. The localized corrosion resistance of the weld metal after welding with an Ar shielding gas supplemented with N2 increased due to a decrease in the pitting resistance equivalent number (PREN) difference between the PRENIR of interdendritic region and the PRENDC of dendrite core. The localized corrosion was selectively initiated at the dendrite core because the PREN of the dendrite core was smaller than that of the interdendritic region.

► In the dendrite core, Cr and Mo were depleted whereas N was enriched.
► The localized corrosion was selectively initiated at the dendrite core.
► The PREN of the dendrite core was much smaller than that of the interdendritic region.
► The tube-to-tube sheet should be welded with an Ar shielding gas supplemented with N2.