Asset management: Quantifying economic lifetime of large-diameter pipelines

Many large-diameter cast-iron water pipelines do not have sufficient historical failure data to enable water authorities to confidently predict failure rates. Yet when these mains fail, the costs-both direct and indirect-can be extensive. This study was undertaken to develop an alternative approach for predicting failure and scheduling replacement. The methodology presented here combines asset condition with a physical probabilistic failure model to determine the expected lifetime of a large-diameter cast-iron pipeline. Net present-value calculations are used to determine the timing of both future inspections and replacement of the entire pipeline. A case study presented in the article provides insight into how this methodology can be applied to a drinking water distribution system. This modeling approach allows asset managers to maximize the usefulness of expensive inspection data and has the potential for improving the management of large-diameter water mains, a challenge that is compounded by an aging asset base and limited budgets. Utilities can apply these findings to help minimize the costs and consequences of failures in large-diameter cast-iron mains.