Hydrogen transport in a duplex stainless steel

Hydrogen permeation through duplex stainless steel membranes of different thickness was studied by the electrochemical technique. The membranes were charged with hydrogen by galvanostatic cathodic polarization in 0.1 M NaOH at 25°C. The first build-up, successive partial decay and build-up transients, and finally, complete decay transients were performed and analysed to determine the real length of diffusion paths (Lα) and the diffusion coefficient of hydrogen (Dα) in the ferrite phase, as well as the hydrogen diffusivity in the austenite phase (Dγ). The diffusion paths in the ferrite phase were tortuous, hence they were longer than the membrane thickness L. The diffusion paths Lα had different lengths in relatively thin membranes (L<0.5mm), but they had the same length in a relatively thick membrane (L=1mm). The hydrogen diffusivity for the ferrite and austenite phases was Dα≈1.5×10−11m2/s and Dγ≈1.4×10−16m2/s, respectively.