The sensitization and intergranular corrosion associated with a phase transformation of tube-to-tubesheet welds of hyper duplex stainless steel were investigated using modified double loop electrochemical potentiokinetic reactivation. The susceptibility to sensitization of the hyper duplex stainless steel tube-to-tubesheet welded with an Ar shielding gas supplemented with nitrogen gas decreased owing to a decrease of the ferrite phase fraction and precipitation of chromium nitrides, thereby increasing the intergranular corrosion resistance. The intergranular corrosion in the hyper duplex stainless steel welds was selectively initiated at the Cr-depleted regions adjacent to the chromium nitride precipitates in the ferrite phases.