Change of pH inside the crevice during crevice corrosion initiation and propagation process of duplex stainless steel

摘要

To elucidate the change of pH inside a crevice during the initiation and propagation processes of the crevice corrosion of the duplex stainless steel, in situ observation of the pH of solution inside the crevice during a potentiostatic crevice corrosion test was conducted. The change of pH over time inside the crevice was measured by a pH sensor which was coated on one side of a crevice former. Crevice corrosion of the duplex stainless steel was initiated at the point where pH lowered about 1.5 locally. The pH at the initiation site of the crevice corrosion suddenly lowered to 0.5, which value was lower than the depassivation pH of both phases of the duplex stainless steel matrix. During the propagation process, pH around the corroded area of the crevice lowered about 0.5, followed by the growth of the crevice corroded area.