(Invited) Atmospheric Corrosion of Metals in Cold and Snowy Region
Authors: Sakairi Masatoshi 
Published: December 2024

Metallic materials such as steels and aluminum alloys are widely used as structural materials from subtropical regions to cold snowy regions. It has been believed that the corrosion rate of metallic materials would be slow in cold and snowy regions since atmospheric corrosion of metals is an electrochemical reaction. However, recent research have reported that corrosion rate change of metallic materials in cold and snowy regions exhibit opposite trend from what would be expected based on temperature [1-3]. The results indicate that severe corrosive environments which expected from the temperature is existed in cold and snowy regions. The possible reason for this severe corrosion environment is accumulated snow on the metals. Due to heating from sunlight and other heat sources, accumulated snow on the metals may melt to form a thin solution layer with concentrated salt for long time. Because, snow is solid and its nuclei of the snow crystal are often salt from sea.

It is well known that corrosion is the main factor for the deterioration of metallic structures such as bridges and automobiles. There is a demand for establishing proper understanding of the corrosion behavior of metals, especially in cold and snowy regions. To elucidate of corrosion behavior, proper data such as corrosion rate of certain materials in actual environments, electrochemical data of metals at low temperature solutions, relationship between corrosion behavior of metals and environmental are required. Therefor, sensing of corrosion rate in several cold and snowy regions, electrochemical observation at subzero temperature, and inspection of corrosion situation of more than 50 years exposed structure and its environmental situation were carried out.

The corrosion sensing using resistance type corrosion senser at Sapporo and Kitami, Hokkaido, Japan, are carrying out form March 2023. The sensing material was iron sheet. The place were selected based on amount of snow and average temperature in winter season. Amount of snow in Sapporo is larger than that in Kitami, while average temperature (form 1991 to 2020) in Kitami is about 5 ˚C lower than Sapporo. In last 30 years average precipitation at Kitami is 70% that of Sapporo. The senser was set on the roof of building and sensing face was faced to south. The senser position was higher than pile up snow fall at each exposure side, therefore senser might not be under the snow for long time. In dependent of exposure site, the corrosion rate of iron was increased after October. The amount of corrosion in Sapporo was larger than that of Kitami.

From the polarization measurements, oxygen diffusion limiting current was observe independent of sample, temperature, and immersion time. The oxygen diffusion limiting current did not decreased with temperature. This result suggested that if the corrosion is governed by oxygen reduction, corrosion rate at low temperature is not low.

The inspected metal structure was made by withering steel and its height was 100 m. The structure was located in the park and more than 10 km from Japan sea coast. In the winter season, the amount of sea salt flown by strong wind form west was almost same as near the ocean side. However, rust formed on weathering steel was in good situation.

Reference

[1] T. Shinohara, A. Tahara, and T. Dara: Proc. of the 5th Asian Materials Data Symposium, Publication House for Science and Technology, Hanoi, 85(2016).

[2] T. Shinohara, T. Tatsuoka, M. Sakairi, K. Azumoi and N. Ohtsu, Proc. of Zairyo-to-Kankyo 2020, Tokyo (2020).

[3] T. Tatsuoka, H. Ichiji, T. Shiaishi, N. Ohtsu, M. Sakairi, T. Shinohara, Proc of Discussion meeting of Zairyo-to-Kanyo, Kurume (2022).