Pressure transients contribute to water company assets’ degradation and structural failure, leading to, amongst other things, leakage and pipe bursts. In recent years, several water companies have undertaken programmes of varying size to capture high frequency pressure data, providing valuable information about the extent of pressure transients across the distribution networks.
However, many such programmes have, justifiably, been driven by the operational needs of the individual water companies and therefore focused on specific network areas/issues. As such, certain network areas, such as non-pumped zones, that are not traditionally associated with having pressure transients, may have been excluded. As an industry, we still do not have a clear picture of the overall frequency and severity of pressure transient with various causes.
This project analyses the distribution and characteristics of pressure transient events. The analysis suggests that, across the whole UK water network, an event occurs once every 1.4 hours, approximately 6,500 events a year. Each one of these events has the potential to cause failure of the water main either by catastrophic failure or increases in leakage.
Most transients are relatively small in size, with a median amplitude of 12.9m/hd. They typically last around 60 seconds. Approximately, 1.2% of transients drop to atmospheric pressure or below, which could cause ingress and water quality concerns. From the analysis, for approximately 60% of transient events, there was a change in pressure from before to after the transient was observed. These changes are most likely associated with a pumping activity, or as the result of a pressure controlling valve. Although the costs and benefits of addressing the root causes of transients will vary from situation to situation, the findings of this report can assist companies in making their own cost benefit analysis.
This study provides an overview of occurrence and severity of pressure transients across the industry. However, it also highlights a lack of the availability, accessibility, and quality of critical data to enable detailed investigations on the impact of the transient on asset failure. Further studies are recommended to understand the characteristics of transients including the variability of pressure changes in the network, transient shape and unique signature, and categorisations of events and root causes. A recommended approach to future logging programmes is laid out so that water companies can get maximum benefit from the data that is collected.