Ex Situ Passivation of Steam Generator Materials

Abstract

Corrosion resistance in alloys such as Inconel 690 is imparted by formation of a thin (50 Å or less), chemically inert, chromium-rich oxide layer on the base metal surface. Once developed, the chromium-rich layer protects the base metal from further corrosion (oxidation). Base metal in this condition is considered to be passive.Under typical operating conditions in a Pressurized Water Reactor (PWR) nuclear power plant, development of the passivation layer on Inconel 690 proceeds in a step-wise fashion, ultimately resulting in a dual oxidation film comprising the passive chromium-rich inner layer and an active nickel-rich oxide outer layer. Oxide development is initially rapid (about 50 percent complete in 50 days); however complete development of the film may take 500 days or longer.