The present work compares seawater corrosion potential ennoblement behavior from two marine
exposure locations using Ni-Cr-Mo alloys. Alloy 625 (UNS N06625), Alloy 276 (UNS N10276), Alloy
4 (UNS N06455), Alloy 59 (UNS N06059) and Alloy 686 (UNS N06686) were exposed for periods of
up to one year at the U. S. Naval Research Laboratory in Key West, Florida (NRLKW), and the
University of Delaware College of Marine Studies at Lewes, DE (Udel CMES). Open-circuit corrosion
potential (OCP) measurements at these two locations demonstrated that the highest achievable
ennoblement-related corrosion potential differed by as much as 100 mV between locations, with higher
potentials measured at the Udel CMES site. A further analysis involving alloy composition
demonstrated that there appears to be some ennoblement biofilm selectivity related to chromium and
iron that influences the highest observable OCP’s, in the coastal waters at Udel CMES. No such
sensitivity to alloy composition appears to be present in the blue ocean waters of NRLKW. Passive film
semiconductive properties are also reported as a result of impedance-derived Mott-Schottky analysis and
photocurrents, with accompanying discussion of their relation to composition for the Ni-Cr-Mo alloys
under investigation.