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

Coupling of metal oxidation in crevice corrosion to both O-2 reduction on surfaces external to the crevice and H+ reduction occurring within the crevice, was studied using a galvanostatic crevice corrosion technique in conjunction with weight loss analyses. Results suggest internal H+ reduction is a significant contributor to the crevice corrosion of the studied alloys in 5 M NaCl at 120 degrees C. Repeat experiments suggest damage can be as much as doubled by H+ 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 O-2 and other oxidants in the service environment may significantly underestimate the actual extent of corrosion on Ni-Cr-Mo alloys. (C) 2018 Elsevier Ltd. All rights reserved.