Effect of Environmental Variables on Crevice Corrosion Susceptibility of Ni–Cr–Mo Alloys for Nuclear Repositories

The crevice corrosion repassivation potential was determined by the Potentiodynamic–Galvanostatic-Potentiodynamic (PD–GS–PD) method. Alloys 625, C–22, C–22HS and HYBRID–BC1 were used. Specimens contained 24 artificially creviced spots formed by a ceramic washer (crevice former) wrapped with a PTFE tape. Crevice corrosion tests were performed in 0.1 mol/L and 1 mol/L NaCl solutions at temperatures between 20 and 90 °C, and CaCl₂ 5 mol/L solution at temperatures between 20 and 117 °C. The crevice corrosion resistance of the alloys increased in the following order: 625 < C–22 < C–22HS < HYBRID–BC1. The repassivation potential (E_CO) showed the following relationship with temperature (T) and chloride concentration ([Cl⁻]) E_CO = (a + b T) log [Cl⁻] + c T + d; where a, b, c and d are constants. At temperatures above 90 °C, E_CO for alloy 625 stabilized at a minimum value of –0.26 V_SCE.