Abstract
Herein, hydrogen uptake and diffusivity in X65 pipeline steel were investigated using the permeation technique under different hydrogen charging conditions. Hydrogen charging was performed using hydrogen gas at different pressures, and electrochemical charging was performed at different cathodic current densities. The results revealed that both the sub-surface hydrogen concentration in lattice and reversible trap sites and the effective hydrogen diffusivity were dependent on the charging conditions. Moreover, the relationship between equivalent hydrogen fugacity and overpotential was determined.