2019 Volume 56 Issue 676 Pages 76-84
The back of manhole cover made of cast iron corrodes extremely in manholes where the concentration of hydrogen sulfide is high. In this study, the corrosion rate of cast iron as a function of the concentration of hydrogen sulfide has been derived. The mean annual concentrations of hydrogen sulfide in 12 manholes were obtained. Corrosion rates of specimens made of cast iron were calculated from mass loss of one‒year exposure in these manholes. The corrosion rate of the specimen increases with an increase in the mean annual concentration of hydrogen sulfide. The relation between logarithms of the two is nearly straight. Dew has acidic properties in manholes where the concentration of hydrogen sulfide is high, because sulfuric acid is produced from hydrogen sulfide. The output of the ACM (Atmospheric Corrosion Monitor) type corrosion sensor increases with increasing relative humidity in a manhole where the concentration of hydrogen sulfide is not detected.
