Age Is a Misunderstood Predictor of Pipe Failure Risk

Pipe age may well be the most common factor used in making water main rehabilitation and replacement decisions. Data from the largest database of pipe failure records compiled to date suggest that it is often being used incorrectly, resulting in billions of dollars in unnecessary pipe replacement. Prior studies have shown a linear relationship between age and failure risk for the first few decades of pipe life. Many models assume that break rates will rise exponentially, despite a lack of published data. This study analyzes over 10,000,000 pipe-years of monitoring records from 6 utilities in 3 continents, providing sufficient data for the longer term relationship between age and break rate to become clear. The results are unexpected: for most pipe materials, failure rates reach a peak after a few decades, and then begin to decrease. This decrease is deep and prolonged for many pipe materials, offering stretches as long as 50 years where failure rates are lower than when the pipes were just a few decades old. These “golden years” extending beyond their design life may offer decades of unexpected useful life from existing pipelines.