EFFECTS OF HYDROGEN ON FITTING SUSCEPTIBILITY OF TYPE-310 STAINLESS-STEEL

Type 310 (UNS S31000) stainless steel (SS) membranes were precharged w ith hydrogen at various current densities. Effects of hydrogen on pitt ing susceptibility were investigated by carrying out the ASTM G 48 sta ndard ferric chloride (FeCl3) tests. Changes in pit density, pit size distribution, average pit diameter(D-a), and apparent pit area percent age (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, increased linearly with the logarithm of t (i.e., D-a, [or A(p)] = alpha ln t + beta). T he value of the coefficient alpha increased with increases in charging current density. The interaction between hydrogen and defects, both i n the surface film and the metal, were used to explain the deleterious effects of hydrogen on pitting corrosion. It was considered that hydr ogen promoted pitting corrosion mainly through the formation of positi ve charge regions around defects In the surface film.