Pipes and apparatus made of carbon steel are used in underground layers, and exposed to underground water environments. To evaluate the corrosion behavior of carbon steel under buried moist bentonite-silica sand condition, corrosion tests were performed using several kinds of corrosion-sensing sensors.

Effect of Al ion on the structure and corrosion protection of rust layer on a carbon steel has been examined. It was found that coexistence of Al ion in atmospheric corrosion environment leads to preferential formation of α-FeOOH structure in the rust layer. Addition of Al ion into heavy-duty coating brings the structural change effect to the rust layer; that is, residual rust consisting mainly of β-FeOOH and Fe₃O₄ on salinity-pre-corroded carbon steel can change its structure to α-FeOOH considerably after applying the heavy-duty reactive paint coating. This change in the structure of rust layer results in higher corrosion protection properties of the reactive paint.

Uniform corrosion penetration prediction model for carbon steel that can be applied in various water quality has been established. It was investigated for the purpose of expanding the knowledge of the corrosion behavior of carbon steel in Fukushima Daiichi nuclear power station of Tokyo Electric Power Holdings Co., Ltd.

The model is applicable to static condition, and flow condition of circular tube. Parameters of the model are temperature, salinity, Larson Skold the Index, average flow velocity and inner diameter of carbon steel tube.

In static water condition, values of corrosion penetration which were predicted by the model were almost the same values as those in the experiments.

In flow conditions in circular tube, values of corrosion penetration which were predicted by the model were within the range from about 0.5 to 2 times of those in the experiments.