Corrosion behavior of carbon steel pipe in environments in which seawater and/or the fresh water was injected

The corrosion behavior of STPG 370 carbon steel piping were studied in order to acquire the key knowledge for discussing the integrity of the cooling water cleanup system piping of the spent fuel pool of the Fukushima Daiichi Nuclear Power Station Units 1 to 4. A series of recirculation pipe tests were carried out in simulated spent fuel pool environments for 6068 h at the longest. The Sch.40 200A pipe was observed to be self-passivated in the test solution of the Larson-Skold index (LSI) = 0.10. The Sch.40 150A pipe was self-passivated in the test solution of LSI = 0.44 as well as that of LSI = 0.10. The test results suggest that the STPG 370 carbon steel piping tends to be self-passivated and consequently tends to suffer localized corrosion damage in actual spent fuel pool environments. In the water chemistry of the current situation for the Fukushima Daiichi nuclear power station of Units 1 to 3, the localized corrosion on the piping of the cooling water purification system made by carbon steel was considered to be likely to occur.