CREVICE CORROSION OF AUSTENITIC ALLOYS IN HIGH-TEMPERATURE WATER

Oxide film characterizations and electrochemical measurements were car ried out on crevices of austenitic stainless alloys to investigate the acceleration mechanism of intergranular stress corrosion cracking (IG SCC) in high-temperature water When the chromium concentration was suf ficient, type 304 (UNS S30400) stainless steel (SS) and alloy 600 (UNS N06600) exhibited good corrosion performance in crevices, forming a c hromium-enriched layer in an oxide film consisting of diiron nickel ox ide (NiFe2O4). When chromium was depleted in the crevice, however the nickel-based alloy exhibited larger weight loss and a thicker film inc luding nickel oxide (NiO) and NiFe2O4. The crevice environment in high -temperature water was characterized by a lower pH (one unit lower) an d a lower corrosion potential (300 mV to 300 mV lower) than in the bul k coater environment. There was a notable increase in the coupling ano de current from the crevice to the free surface when the chromium-depl eted phase was located in the crevice. IGSCC was accelerated in crevic e by the higher corrosion rate with less protective film at the chromi um-depleted phase, with the differential potential cell between the fr ee surface and increvice in high-temperature water.