Influence of H₂S concentration and pH value on corrosion behavior ofweld joint of X65 subsea pipeline steel

With an autoclave the environment of submarine gathering system was simulated, then in which the influence of concentration of H₂S and pH value on the corrosion behavior of weld joints of X65 pipeline steel was investigated by electrochemical techniques, immersion test, SEM and XRD analysis technique. The results show that the free corrosion potential of different portion of the X65 pipeline steel weld joint exhibited a tendency of decrease, but the corrosion density of increase, corresponding to the following order as: the weld seam, the heat affected zone and the base material. The average corrosion rate of the steel weld joints is in the range of 0.1~0.25 mm/a, the increase of the concentration of H₂S and the reduction of the pH value can both lead to the increase of corrosion rate. The corrosion mode of weld seam of X65 steel is mainly the uniform corrosion in the simulated environment, and the corrosion of weld seam is slighter than that of the heat affected zone.