Experimental studies on the local corrosion of low alloy steels in 3.5% NaCl

An occluded corrosion cavity (OCC) simulated cell was designed to study the auto-catalyzing process of low alloy steels. The effects of geometrical factors and area ratio of anode/cathode on the auto-catalyzing process have also been analyzed. The local corrosion rates of low alloy steels in 3.5% NaCl were ranked by this cell. While, multi-cycle scanning potentiostatic polarization measurements was also developed to evaluate rapidly the degree of the auto-catalyzing process inside the OCC. The results obtained by these two methods are in good agreement with the results obtained by an immersion corrosion test carried out in sea water. Based on the SEM results, "microscopic area difference" (MAD) effects and "dispersed carbides strengthening" (DCS) effects are submitted to explain the difference in the auto-catalyzing process of low alloy steels. MAD will have an effect on anode occluded process and DCS effect, quantities and distributions of carbides in an OCC affect the property of film formed. The intrinsic properties of materials are the reasons for these two effects, while the presence of locally occluded surface is an essential environmental factor. (C) 2001 Elsevier Science Ltd. All rights reserved.