The Effect of CRA Oxides on Hydrogen Permeation under Cathodic Protection Conditions

Abstract The effect of oxides on hydrogen uptake and diffusion in corrosion resistant alloys (CRA) under cathodic protection conditions was investigated by use of the electrochemical hydrogen permeation method with the unique added feature of in-situ removal of the oxide film by introducing a grinding stick in the cathodic cell compartment. Three CRA materials with different contents of Cr and Mo were tested. Initial oxides were formed prior to hydrogen charging that were removed by in-situ grinding in the cathodic cell of the permeation setup while keeping the cathodic polarization constant. Prolonged (130-500 h) cathodic charging was also performed to observe how the hydrogen permeation changed with time when the protective oxide was changed or cathodically reduced. Removal of the initial oxide film by in-situ grinding enhanced the cathodic charging current density, while the hydrogen permeation – in contrast – decreased. Prolonged cathodic charging caused a continuous decay in hydrogen permeation. The results were qualitatively interpreted as that increased oxide presence/thickness/quality(low level of defects) increased the hydrogen uptake by promoting the surface coverage of atomic H. Characterization of the surface oxides tested herein was not done and could be done in future work.