Environment induced cracking of advanced steam turbine blade steels

Coal and gas-fired power stations, nuclear fission reactors, projected nuclear fusion reactors and concentrated solar thermal (in some systems) have the commonality that they heat water to produce steam, which subsequently drives a turbine to generate electricity. The current drivers in these technologies are reducing emissions, lowering the cost of electricity generation, and maintaining power availability. In supporting these goals, it is critical that developments in steam generating technology are matched by advances in turbine efficiency. To that aim, turbine manufacturers are exploring improved design of the blading and development of more compact turbine layouts. In blade design, attention is being focused on improved aerodynamics of the last row blades in low-pressure (LP) steam turbines.  Higher strength alloys will be necessary but it is essential for these highly stressed blades that any proposed alloy should provide similar or, preferably, improved resistance to corrosion and environment induced cracking by comparison with currently-used alloys.   
The 11-13Cr series of alloys such as FV566 with strength levels about 900 MPa at ambient temperature has been the basis of most turbine blade systems. There has been much service experience and laboratory testing and there is bank of information available albeit with some gaps in predictive capability. The higher alloyed precipitation-hardened stainless steel PH13-8 blade steel with a strength level of about 1300 MPa, originally developed for aircraft undercarriage applications, is being considered as a potential candidate for the advanced turbine blade but stress corrosion cracking and corrosion fatigue data are limited. The usual expectation is that susceptibility to environment induced cracking of steels will increase with strength length level but for turbine blade applications such increased vulnerability would be deemed unacceptable.  Thus, extensive testing is being undertaken to fully characterise the performance of this alloy with respect to resistance to both stress corrosion and low cycle corrosion fatigue based on a fracture mechanics approach using precracked specimens in fully immersed simulated condensate environments. The results from this investigation will be compared with data obtained for the conventional FV566 steel.