Measures Against Electrolytic Rail Corrosion in Tokyo Metro Subway Tunnels

Tokyo Metro Co., Ltd. is operating nine railroad lines (195.1 km) forming a network mainly consisting of subways in Tokyo, the capital of Japan. Good maintenance of tracks is essential to the safety of passengers. However, rail breakage due to electrolytic rail corrosion is occurring in some underground spaces. Rail corrosion occur frequently in subway tunnel due to underground water leakage. For some place, we have to change rails every a half year. So it is big problem for underground space. We have been examining electrolytic rail corrosion for three years. By producing maps of places prone to electrolytic rail corrosion, divided into 25-m sections, we analyzed track conditions and identified the causative factors of electrolytic corrosion depending on track conditions. In addition, we focused our attention on chemical approaches to the prevention of electrolytic corrosion. First, we conducted chemical analyses of samples of electrolytic corrosion products and samples of water collected from the environment where electrolytic corrosion occurred. The results suggested that akaganeite, which forms in the high Cl- concentration in underground spaces. promoted the loss of rail strength. Next, we examined the effectiveness of the sacrificial metal method in delaying electrolytic corrosion. The use of zinc, a metal with higher ionizing tendency than iron, in the form of adhesive tape attached to steel surfaces, was effective in delaying electrolytic rail corrosion. This report discusses the details of the conventional physical approach relying on rail replacement planning and the chemical approach to the prevention of electrolytic corrosion with some insight into future developments.