CREVICE CORROSION PROPAGATION ON ALLOY-625 AND ALLOY C276 IN NATURAL SEAWATER

Chemical composition of the aqueous solution within crevices on two di fferent Ni-Cr-Mo-Fe alloys immersed in natural seawater was determined using a semiquantitative thin-layer chromatographic method. Active cr evices were found to contain concentrated amounts of dissolved Ni2+, C r3+, Mo3+, and Fe2+ ions. Propagation of crevice corrosion for the two alloys was determined from anodic polarization curves in model crevic e solutions based upon stoichiometric dissolution or selective dissolu tion of alloy components. Both alloys 625 (UNS N06625) and C276 (UNS N 10276) underwent crevice corrosion in the model crevice electrolytes, For the model crevice solution based upon selective dissolution of all oy constituents, the anodic dissolution rate for alloy 625 was higher than that for alloy C276. This trend was reversed for the model crevic e solution based upon uniform dissolution of alloy constituents.