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 mV_Ag/AgCl) and temperature (10 °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 $$ at -1050 mV_Ag/AgCl varied from 1.81 to 2.86 × 10^-15 m²/s across the temperature range of 10-23 °C. The effective subsurface hydrogen concentration $$ was influenced by both the applied temperature and overpotential. Particularly, the change in $$ at 10 °C is dependent on the hydrogen absorption efficiency affected by the surface coverage fraction of hydrogen. Furthermore, the hydrogen fugacity on the sample surface $$ , the applied overpotential, and the temperature have been successfully cross correlated to interpret hydrogen evolution and adsorption. It was demonstrated that $$ primarily changed with the applied overpotential, while the temperature affected the gradient of $$ 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.