Hydrogen diffusion and uptake in nickel Alloy 625 under cathodic protection conditions

Hydrogen diffusion and uptake in nickel Alloy 625 under cathodic protection potential (-1050 mVAg/AgCl) and temperature (10 degrees C) were studied using electrochemical permeation tests. It is the first time hydrogen permeation of nickel alloy at a temperature lower than room temperature was investigated. The results revealed that the effective diffusivity of hydrogen Deff at -1050 mVAg/ AgCl varied from 1.81 to 2.86 x 10-15 m2/s across the temperature range of 10-23 degrees C. The effective subsurface hydrogen concentration Csub was influenced by both the applied temperature and overpotential. Particularly, the change in Csub at 10 degrees C is dependent on the hydrogen absorption efficiency affected by the surface coverage fraction of hydrogen. Furthermore, the hydrogen fugacity on the sample surface fH2, the applied overpotential, and the temperature have been successfully cross correlated to interpret hydrogen evolution and adsorption. It was demonstrated that fH2 primarily changed with the applied overpotential, while the temperature affected the gradient of fH2 during the potential increment. The current study provides valuable insights for industries, assisting in the prediction of hydrogen absorption and hydrogen-assisted failures in subsea nickel alloy components.