engleski

The Influence of Biospecies and some Inhibitors on Crevice Corrosion of Stainless Steel in Natural and Biological Inert Seawater

It was recognized by many authors that bio-films consisting of different micro-organisms formed on the metal surface in the seawater shift the free corrosion potential up for some decades and increase the oxygen reduction rate. In a such way bio-film settlement may stimulate crevice corrosion. It means that properties of a bio-film are in competition with protective layer of stainless steel in natural seawater. In the actual work crevice corrosion initiation and propagation of austenitic stainless steel UNS S31600, 316L have been studied in the natural seawater, from the Adriatic Sea, at the location in Dubrovnik, Croatia, and in the biological inert seawater, seawater treated 10 minutes at 100°C from the same locality. In another series of experiments inhibition effect of two carboxylate salts, environmental friendly compounds, was investigated, which may contribute to the repassivation of the metal surface. Among several crevice corrosion tests, often mainly of comparative nature aimed at ranking alloys for the environmental use a relatively new method was used, developed by a research group, Crev Corr of Marine Corrosion Working Party of the EFC, in which our Laboratory also participated. The test takes into account a number of inter-related factors strictly defined, as the geometry of crevice mode, spring loaded crevice formers used, gasket materials, the surface finishing and the electrochemical potential increase rate. Experiment were performed in stirred natural and biological inert seawater respectively at 20°, 30° and 40°C under atmospheric condition. After exposure crevice formers were removed for visual and microscopic inspection of crevice area on specimens. The blend of inhibitors improved crevice corrosion resistance in both investigated media due to an increase of the metal surface passivity.

crevice corrosion; seawater; biological inert seawater; inhibitors

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