Stainless steels and nickel based alloys are sometimes used for seawater applications in the Oil and
Gas sector. The crevice corrosion performance of selected alloys was investigated in natural and chlorinated seawater, at different temperatures. To better understand and quantify the effect of crevice geometry, several crevice configurations simulating service conditions were evaluated including flanges assembled with gaskets, bolts mounted with nuts to plates, and the standard CREVCORR-type crevice formers. The crevice geometry was confirmed to be of major importance in terms of risk for initiating crevice corrosion. In natural seawater (i.e. not chlorinated), the most severe temperature was 30°C, due to high biological activity and the increase in the kinetics of corrosion. Chlorination at 0.5 ppm increased the risk of initiation but decreased the rate of propagation of crevice corrosion. In chlorinated seawater, the risk of initiation of crevice corrosion was significantly increased with temperature for all tested alloys. For each of the tested stainless steel configurations, the superaustenitic UNS S31266 showed better crevice corrosion resistance than superaustenitic UNS S31254 and S34565, superduplex S32750, and also nickel-based alloy N06625. The nickel-based alloy UNS N06022 showed better crevice corrosion resistance than all the other tested alloys.
Key words: Crevice corrosion, stainless steels, Ni-based alloys, natural seawater, chlorination, crevice geometry, assemblies