The effects of mixtures of H2O and H2S with H2 gas, upon H diffusion and permeation in austenitic and ferritic stainless steels, were studied by using a gas-phase permeation technique at temperatures of between 100 and 360C (figure 20). The effective H diffusivity and permeability from atmospheres of H2, H2O and H2S, into Pd-coated deformed AISI304 at 320C, was such that the effect of H2 was similar to that of H2S. Both effects were greater than that of H2O. In uncoated AISI 302, both diffusion and permeation from H2O were consistently less than the equivalent values for H2. Additions of H2O and H2S to H2 gas reduced both H diffusion and permeation. The extent of reduction in a ferritic alloy was greater than that in an austenitic alloy. A Pd coating was effective in protecting the metal matrix from reaction with H2O. However, H2S interacted strongly with the Pd coating. The oxidized surface could be completely recovered by heating in pure H2 gas at 320C, but the sulfidized surface could not.

T.P.Perng, C.J.Altstetter: Acta Metallurgica, 1988, 36[5], 1251-60