As the age of systems structures and components (SCCs) in nuclear power plants increase so does the level of effort to manage their aging. Half of the nation’s nuclear plants are over 30 years old with essentially all of the remainder older than 20 years. For safety related service water systems operating experience (OE) has shown that life spans of 25 years or more can be achieved without significant or concerted attention to mitigate internal corrosion. Nonetheless plants are being challenged by regulators and plant management to define where their service water systems are in the life cycle management process and further predict with enhanced confidence the future levels of required maintenance inspections and engineering support. A significant portion of service water piping can be buried and not easily assessed. OE demonstrates that the condition of internal surfaces (i.e. internal corrosion) of buried and underground piping can be inferred from inspections of internal surfaces of above ground piping where the component material environment and ageing effects are similar.The purpose of this paper is to discuss a statistical method for quantitatively predicting piping thickness and leakage over time provide context for the interpretation of results and define confidence for those results. This will include a case history that demonstrates the application of a statistical model for buried and above grade segments of a service water system benchmarking the model’s predictions and the use of the model to prepare and plan maintenance and financial support up to license renewal and into the period of extended operation (PEO).