2004 Volume 53 Issue 3 Pages 143-148
The geothermal energy is desirable as one of the energy resources for the global environmental protection, since it scarcely emits carbon dioxides (CO2) as compared with the conventional fossil fuels. The geothermal fluid contains a large quantity of corrosive chemicals which occasionally cause the corrosion-related problems such as stress corrosion cracking (SCC). Therefore, the evaluation of the corrosion resistance of the materials applied to the steam turbines is indispensable for the economical and effective utilization of the geothermal energy. In this work, SCC growth behavior of the blade materials (13%Cr and 16%Cr-4%Ni stainless steels) and the rotor material (1%Cr-Mo-Ni-V steel) for geothermal steam turbines were investigated by means of WOL specimens immersed in the corrosive water of the simulated geothermal environment including chloride and sulfate with the carbon dioxide and hydrogen sulfide. As the results, SCC growth rate da/dt and critical stress intensity factor KI SCC of the materials tested were calculated. The blade material 13%Cr steel showed crack growth with relatively low stress intensity factors under the tested condition, while the blade material 16%Cr-4%Ni steel with the improved heat treatment showed no crack growth. It was also clarified that the 1%Cr-Mo-Ni-V steel used as a rotor material had an excellent SCC resistance.