The Effect of [Cu(EDTA)] on crevice corrosion of type 316L stainless steel

Aoyama, Takahito   ; Kato, Chiaki   

Alloyed Cu is known to inhibit the growth of pitting corrosion on stainless steels after pitting initiation. The Cu dissolved from the stainless steel matrix acts as an inhibitor in acidic chloride environments which is formed in pits. The Cu suppresses active dissolution rate inside the pits. This suppression effect is supposed to be also effective for active dissolution which promotes crevice corrosion. Therefore, if it is possible to introduce Cu to the inside of a crevice from the outside, introduced Cu is supposed to inhibit crevice corrosion on stainless steel. However, diffusion of ions between inside and outside of the crevice is restricted by its geometry, and Cu does not migrate to inside of a crevice according to the electroneutrality principle. [Cu (EDTA (ethylenediaminetetraacetic acid))] is a chelated Cu which has negative charge, and is expected to migrate to inside of a crevice from the outside by electrochemical migration. In addition, it is reported that Cu in [Cu(EDTA)] could be easily substituted by Fe in low pH. Therefore, Cu is considered to be introduced to the inside of the crevice as [Cu(EDTA)], and to affect crevice corrosion of stainless steel. In this study, in situ observation of an inside of the crevice was performed to analyze the effect of [Cu(EDTA)] on crevice corrosion.