Lessons Learned from Large-Diameter Pipe Failure Case Studies

Failures of large diameter pipes can cause significant social, environmental and economic impacts. The actual failure mechanisms of buried pipes are difficult to isolate because many external and internal factors are commonly involved. Moreover, the major pipe breaks occur below the ground and the root cause of failure may be masked by the violent nature of the break. Detailed investigations were undertaken to examine and understand the failure mechanisms of buried large diameter cast iron water pipe breaks. We used various approaches to gathering field evidence from failed as well as unfailed pipes, numerical simulations, field instrumentation and full-scale laboratory pipe burst testing. Large diameter pipes tend to fail predominantly by longitudinal fracture. The failure mechanisms involving longitudinal fractures indicated that a large corrosion patch in the pipe barrel is commonly needed for pipe failure. This finding is in contrast to the belief that small pits are mostly responsible for failures. This means that many of the current condition assessment techniques currently targeting the detection of pits in pipes need to focus on the detection of larger patches of corrosion. The research also found that pipes fail by developing a crack first within a corrosion patch that could lead to water leakage until the crack grows sufficiently long to cause a major break. This concept is referred to as “leak before break” (LBB) for cast iron pipes. This concept can potentially be used for failure prevention of critical pipelines through improved leak detection.