It has been recognized for many years that the environment surrounding a fatigue specimen (or structural component) can interact in a manner that can degrade the fatigue response.This is true for both the processes of fatigue crack initiation and fatigue crack propagation (FCP).Following the pioneering work of Kondo and co-workers over twenty years ago, a phenomenon generally known as environmentally-assisted cracking (EAC) has received a great deal of attention in the nuclear industry worldwide because it has the potential to cause significant severe in-service crack extension. For example, Anderson et al have shown that some cracks smaller than those that can be reliably detected are predicted to grow to unacceptable sizes when subjected to the maximum fatigue usage factors allowed by Section III of the ASME Boiler and Pressure Vessel Code (hereafter called the Code) and the present EAC curves from Section XI of the Code.