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Type 310 (UNS S31000) stainless steel (SS) membranes were precharged with hydrogen at various current densities. Effects of hydrogen on pitting susceptibility were investigated by carrying out the ASTM G 48 standard ferric chloride (FeCl 3 ) tests. Changes in pit density, pit size distribution, average pit diameter (D a ), and apparent pit area percentage (A p ) with hydrogen charging current density and immersion time (t) were measured statistically. Hydrogen in type 310 SS significantly promoted pit initiation and pit growth. D a and A p increased linearly with the logarithm of t (i.e., D a [or A p ] = ␣ ln t + ␤). The value of the coefficient ␣ increased with increases in charging current density. The interaction between hydrogen and defects, both in the surface film and the metal, were used to explain the deleterious effects of hydrogen on pitting corrosion. It was considered that hydrogen promoted pitting corrosion mainly through the formation of positive charge regions around defects in the surface film.

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