2004 Volume 53 Issue 12 Pages 568-575
The materials of the attachment near the last stage of fossil power plant low-pressure steam turbines will be exposed to the severe corrosion condition due to the concentration of corrosive chemicals by the alternating dry & wet environment, of which phenomenon will be caused by the frequent shutdown and the load change of power plants. The SCC behavior of low-pressure steam turbine materials is evaluated by four kinds of SCC tests and the electrochemical corrosion methods. For all materials “3.5NiCrMoV, 12Cr and 17-4PH steels”, the ion which induced the most severe SCC sensitivity was the chloride ion (Cl-), the next severe one was the sulfate ion (SO42-) and the sodium ion (Na+) showed almost no SCC sensitivity. Especially, the coexistence of the chloride ion and oxygen accelerated remarkably the SCC sensitivity of all materials tested. From the consideration between the SCC sensitivity and characteristics of the corrosion film, it was shown that the Cr content in the materials controls the SCC sensitivity and also the corrosion potential. This is due to the formation of the passive Cr2O3 film.