The hydrogen diffusion in 2.25Cr-1Mo steel used in the wall of hydrogenation reactors was studied by electrochemical permeation. The diffusion coefficient increased, with thickness, between 0 and 1.6mm but the D value remained constant when the thickness of the steel membranes was greater than 1.6mm. The diffusion coefficient as a function of temperature could be expressed as:

D(m2/s) = 2.097 x 10-6exp[-30358/RT]

This equation could be used to calculate the atomic hydrogen concentration distribution resulting from hydrogen permeation in the wall of an hydrogenation reactor at high temperatures and pressures.

Hydrogen Diffusion in 2.25Cr-1Mo Refractory Steel. G.Yu, X.Zhang, K.Ke, Y.Du: Acta Metallurgica Sinica, 1999, 35[7], 755-8