A comparison of release rates of Cr, Ni, and Fe from stainless steel alloys and the pure metals exposed to simulated rain events

The aim of this study is to demonstrate differences in metal release rates of Cr, Ni, and Fe from pure metals and stainless steels alloys (grades 304 and 316) exposed to identical simulated rain events. Panels were exposed to two 8 h continuous rain periods, separated by a 40 day dry period, in a specially designed rain chamber which permits artificial rain of known composition to be introduced at a given intensity. The study is intended to provide further knowledge of the behavior of stainless steels exposed to atmospheric corrosion and to show the discrepancy between estimated release rates based on nominal alloy composition and actual, measured release rates. Release rates of Fe and Ni were found to be substantially higher from the pure metals than from the stainless steels due to the presence of a chromium-rich surface film. The release rate of Cr was similar for stainless steel alloys and pure chromium. X-ray photoelectron spectroscopy investigations after single-rain events showed chromium to be enriched in the surface film upon rain exposure resulting in decreasing release rates of Cr, Ni, and Fe. Comparison between actual release rates of alloy constituents and calculated rates based on the pure metals and the nominal alloy composition, showed calculated data to substantially overestimate release rates of Ni and Fe. (C) 2004 The Electrochemical Society.