An overview is given of current knowledge and understanding of environment induced
cracking of steam turbine discs and blades. There has been extensive research on this
theme, though our ability to predict the impact of environmental variables on service life is still
constrained as early research had focused on environments that were not always
representative of condensates formed in service. More recent research has yielded insight
into the evolution of damage from pits and has provided more detailed long crack growth
rates but the growth of cracks in the short crack regime is largely undetermined. For aging
coal-fired plants, the advent of two-shifting (switching on and off-load on a daily basis) will
lead to a reduction in remnant life due to transients in stress and environment. Since the
number of cycles is small the impact of load cycling is predicted to be modest. However,
there may be an effect of the transient exposure to oxygen off-load on the subsequent crack
growth rate on-load and this also needs to be accounted for in life assessment.