Localized Corrosion of Al-clad Steel Wire in the Coastal Area
Hisayoshi Takazawa, Ryouji Takekoshi, Yoshimori Miyata, Hiroyuki Saito
Localized corrosion mechanisms of Al-clad steel wire strand under sealing tape in the coastal area were studied mainly by laboratory accelerated corrosion testing. The results are summarized as follows: (1) The same-type localized corrosion of Al-clad steel wire strand found in the field was also observed during laboratory testing. (2) Alkaline areas coexisted with acid areas at corroded regions for both the laboratory-tested specimen and the corroded strand in the field. (3) The corrosion might be a kind of “crevice corrosion” caused by destruction of passivation film of Al layer in the crevice between sealing tape and Al-clad strand. In the crevice, chloride ions might be concentrated and oxygen supply might be restricted. (4) Regarding this “crevice corrosion”, a reduction of oxygen as a cathodic reaction of corrosion cell proceeded within the crevice, whereas in the typical crevice corrosion, such as that of stainless steel in chloride solution, cathodic reaction proceeds outside the crevice. (5) This difference might be due to the passivation film stability difference between Al and stainless steel. The passivation film of Al can be destroyed under high oxygen conditions where oxygen reduction could proceed sufficiently as a cathodic reaction of crevice corrosion cell.