PPXX: Unlocking Model Predictions of Slow Crack Growth in PVC-U Pipes for the Dutch Water Utilities

Abstract

Pipe failure in drinking water distribution networks occurs as a result of high loadings on the pipe. Especially, pipes that deteriorate over time have an increasing probability of failure. Prediction models that estimate when a particular pipe will fail are therefore valuable tools in pipe replace- ment strategies. To this end, a computational tool was developed that several Dutch utilities are now combining with their decision support tools for asset management (Wols et al., 2018).

The tool consists of a numerical model that predicts the pipe stresses and joint rotations as a result of different loadings on the pipe (vertical soil load, water pressure, traffic, differential soil settlement). The model follows as much as possible physical principles to predict pipe failure, combining physical load models, degradation models and a description of the pipe and its surroundings. Failure occurs when the resulting von Mises stress or the resulting joint rotations exceed their maximum allowable values. The objective of the presented work is to implement the current knowledge about the aging of PVC-U, the prevalent pipe material in the Netherlands. In this way, the extensive work of authors such as Breen and Boersma (2006) and Burn et al. (2005) becomes accessible for the water utilities to support their decisions.

After expansion of the tool with PVC-U-specific aspects such as LEFM slow crack growth under hoop stress, including residual stress, a sensitivity analysis of the total model is conducted to visualize the dominant factors in pipe failure. The analysis is as much as possible based on ranges of parameter values encountered in the field by utilities during measurements between 2007 and 2017 (Mesman and van Laarhoven, 2018), following the methods of the initial surveys by Breen and Boersma (2006). By probing the combined failure-, degradation and loading mechanisms in a single model, one acquires more insight into their interrelation and into the contribution of each to the total process. This information helps utilities to prioritize their efforts concerning exit assessments and inspection.