Investigation of crevice corrosion of AISI 316 stainless steel compared to Ni-Cr-Mo alloys using coupled multielectrode arrays

Close-packed coupled multielectrode arrays simulating a planar electrode were used to monitor 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 x(crit)(2) vs G and x(crit)*(2) vs G derived from polarization data in simulated crevice solutions guided the implementation of rescaled crevices with greater spatial resolution. x(crit) and x(crit)* are the distances from the mouth to the location where the potential reaches two different critical values, and G is the crevice gap. Scaling laws were also used along with anodic polarization data in simulated crevice solution to predict crevice corrosion behavior of alloy 22 (UNS N06022). Crevice corrosion of AISI 316 stainless steel in 0.6 mol/L NaCl at 50 degrees C readily initiated close to the crevice mouth (i.e., x(crit)approximate to 0) at modest applied potentials (e.g., E-app=0 V-SCE) and spread both inward and outside the crevice with time. Crevice corrosion initiated farther inside the crevice (i.e., x(crit) is large) and required higher applied potentials (e.g., E-app=50 mV(SCE)) in the case of alloy 625. The local crevice current density increased dramatically over a short period of time to reach a limiting value in the case of AISI 316; while metastable dissolution behavior over a large area was observed for alloy 625. The ramification of the larger critical depth for Ni-Cr-Mo alloys toward crevice corrosion susceptibility in the case of crevice formers of finite length is discussed. Crevice corrosion shifts to the mouth of the crevice for the less corrosion-resistant materials in crevice solutions saturated in metal salts but remains confined at a distance x(crit) for alloy 625 under the conditions tested. (C) 2008 The Electrochemical Society.