PROBABILISTIC MODEL TO PREDICT LONGITUDINAL FRACTURE FAILURE OF BURIED PVC PIPES

To resolve the longitudinal fracture failure problems for the buried PVC pipes with inherent defects under the complex stress induced by loads, the failure prediction model was developed, taking circumferential mechanical characters of pipes and a crack growth model into consideration. Monte-Carlo (MC) simulations were used to perform the probabilistic analysis, because of the uncertainty of the model and parameters. Results show that it is suitable to adopting the failure prediction model to calculate the failure rates, because the calculated values agreed well with the measured data. The crack growth rate increased with time under constant external stresses. The pipes with larger defect sizes had shorter lifetimes. The failure rate when considering all of random variables was two times that of only considering the initial defect as a random variable, and it reached the maximum within 20 years, then slowed down gradually. The initial defect sizes, internal pressure, residual stresses and pipe thickness have large influence on the lifetime of PVC pipes. Increased internal pressure and residual stresses lead to increase failure rates. An accurate probability distribution of the initial defect is most important to calculate the failure rates. Reducing initial defect sizes by using suitable production process and installation technology can effectively extend the service life.