The role of internal cathodic support during the crevice corrosion of Ni-Cr-Mo alloys

Coupling of metal oxidation in crevice corrosion to both O2 reduction on surfaces external to the crevice and Hþ reduction occurring within the crevice, was studied using a galvanostatic crevice corrosion technique in conjunction with weight loss analyses. Results suggest internal Hþ reduction is a significant contributor to the crevice corrosion of the studied alloys in 5 M NaCl at 120/C14 C. Repeat experiments suggest damage can be as much as doubled by Hþ reduction. This process, however, can be minimized by alloying additions of Mo, which permit the deposition of Mo-rich corrosion products within an active crevice. Due to difficulties experienced during corrosion product removal, the results presented herein are anticipated to be underestimates of the actual extent of this process. Consequently, damage predictions based on the availability of O2 and other oxidants in the service environment may significantly underestimate the actual extent of corrosion on Ni-Cr-Mo alloys.