港湾環境における埋設鋼材の腐食速度測定 (第2報)

抄録

Marine environments for buried steel structures consist of sea water and various soil zones (mud, silit, sand, etc.). At the boundary between different zones, macro-corrosion may occur on the anodic side of steel surface.
As it has been experimentally proved that for buried steel structures macro-corrosion may be more dangerous than micro-corrosion, so we studied at first the estimating method on macro-corrosion rate between two zones as described below. By analizing the data in the 1st report, we got cathodic polarization resistance, γ_c (Ω-cm²), as a controlling factor for the corrosion rate of buried steel structures and obtained the following relation: C=0.34e-(γ_c/10⁴) where, C: micro-corrosion rate (mm/yr), γ_c=[1.2-12×2, 000×(I_KD×10^-6)]/(I_KD×10^-6) (Ω-cm²), I_KD: galvanic current density (μA/cm²).
But since it is considered difficult to determine macro-corrosion rate at the boundary by γ_c alone, we carried out some experiments to find other controlling factors. As the result, the ratio of anodic and cathodic surface areas of test pieces was found to be another controlling factor; namely, with decreasing the ratio from 1:1 to 1:4, the macro-corrosion rate doubled.