The flow of H through this steel was strongly affected by surface reactions. An experimental investigation which was based upon pressure modulation techniques showed that macroscopic flow could be described by:

D (m2/s) = 7.3 x 10-7 exp[-6300/T]

and

P (mol/s m Pa½) = 8.1 x 10-7 exp[-8190/T]

plus a surface reaction of the form:

H2 (gas) → 2H (solid)

The rate constant for this reaction ranged over an order of magnitude at each temperature, and depended upon the surface preparation. The fastest reaction occurred on in situ H-ion beam-cleaned surfaces. The surface coefficient for this case was:

K (mol/s m2Pa)= 0.032 exp[-9710/T]

Hydrogen in 316 Steel - Diffusion, Permeation and Surface Reaction. D.M.Grant, D.L.Cummings, D.A.Blackburn: Journal of Nuclear Materials, 1988, 152, 139-45