The effect of hydrogen on the stress corrosion cracking (SCC) of API X-65 pipeline steel in near-neutral pH environments was studied using cyclic voltammetry, hydrogen electrochemical oxidation current measurements and slow strain rate tests (SSRT). All the tests were performed in solution consisted of 0.1, 0.01 and 0.005 M sodium bicarbonate (NaHCO 3 ), at both room temperature and 60 ?C. The oxidation currents were obtained for the hydrogen pre-charged specimens maintained at a certain positive potential in dilute NaOH electrolyte. Hydrogen concentrations in cathodically pre-charged specimens were estimated by calculating the area under the current curve. The results showed that hydrogen oxidation current increased with decreasing solution concentration and was maximum for 0.005 M NaHCO 3 at 60 ?C. Combined with SSRT results, it is found that the high susceptibility to SCC is always connected to a high hydrogen concentration in steel. In addition, the fracture surfaces of specimens were observed in a scanning electron microscope (SEM). Specimen tested in air, exhibited a ductile type of failure, conversely, those tested in corrosive solution showed brittle fracture composed of microcracks just near the surface. These microcracks were found more frequently in the specimen tested in 0.005 M NaHCO 3 , so it might be due to the effect of high hydrogen concentration in steel.
