Investigation of Crevice Corrosion of AISI 316 Stainless Steel and Ni-Cr-Mo Alloy 625 Using Coupled Multi-Electrode Arrays

Close packed coupled multi-electrodes arrays (MEA) simulating a planar electrode were used to measure the anodic current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel (UNS S31600) and Ni-Cr-Mo alloy 625 (UNS N06625). Scaling laws derived from polarization data guided the implementation of rescaled crevices providing spatial resolution. Crevice corrosion of AISI 316 stainless steel in 0.6 M NaCl at 50°C was found to readily initiate close to the crevice mouth (i.e., xcrit ≈ 0) at modest applied potentials (e.g., Eapp=0 VSCE) and to spread inwards and outside the crevice with time. In the case of alloy 625, crevice corrosion initiates further inside the crevice (i.e., xcrit is large) and requires higher applied potential (e.g., Eapp=50 VSCE). The local crevice current density increased dramatically over a short period to reach a limiting value in both cases. The ramification of the larger critical depth for Ni-Cr-Mo alloys towards crevice corrosion susceptibility is also discussed.