AWWA DSS62070

In the absence of historical failure data, physical probabilistic models based on fracture mechanics are under development to estimate failure rates in buried PVC and PE pipelines. A model for PVC pipes has been completed and uses linear elastic fracture mechanics (LEFM) to predict time to failure. Although LEFM is valid for PVC pipes, the development of a large craze zone during PE pipe fracture necessitates the use of elastic plastic fracture mechanics (EPFM) theory. An EPFM-based model for PE pipes is under development and some preliminary results are presented. In both models, inherent defect size in the pipe wall is represented as a stochastic variable, based on microscopic examination of field failures in PVC pipes. In the absence of sufficient defect size data, the variation in defect size in PE pipes is assumed to follow that for PVC pipes. Monte Carlo simulation is then used to estimate the probability of fracture failure for a pipe with a defect in its wall. The resulting physical probabilistic failure models show good agreement with actual PVC pipe failure data recorded by United Kingdom water utilities. While agreement is also encouraging for PE pipes, values of operating pressures used in the model are significantly higher than those expected in service. Future development of the model is proposed to include the effect of excessive external loads on PE pipe failure rates. Includes 18 references, tables, figures.