Leakage Characterisation in Bulk Pipes using Pressure Tests

Master Thesis


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The supply of water is becoming increasingly strained as the demand for this essential and limited resource continues to increase. A significant amount of this resource is, however, lost through leakage. Not only does this result in a waste of a precious resource, but it also leads to a direct loss of revenue, especially considering that value has been added to the leaking water through collection, storing, purifying and pumping. A great deal of research has been done on reducing water leakages in distribution networks, however, leakage in bulk pipelines has received comparatively little attention thus far. In this study, bulk pipelines in the field were tested with a pressure testing device developed by the University of Cape Town. With this device, a range of pressures were applied to various pipeline sections and the corresponding leakages were measured, resulting in characteristic pressure-leakage relationships. The Fixed and Variable Area Discharge (FAVAD) and the empirical N1 leakage models were then applied to interpret the pressure-leakage relationships. Thirteen tests were attempted on pipeline sections ranging from 300 mm to 600 mm in diameter, and pressure tests were successfully performed on eight of the thirteen sections. Even though the effectiveness of the testing technique is dependent on the sealing capability of the isolation valves, it was found that most valves sealed effectively, with only two pipelines sections failing to isolate. The high elevation differences along the length of the pipelines were found to have a dominating effect on the characteristics of the leak, which made it possible to roughly estimate the most likely leak locations by comparing the observed leak characteristics to those found in literature for similar conditions. The dependence of the leak characteristics on the location means that both have to be determined simultaneously. This can benefit the analysis, as some locations may be excluded based on their unrealistic leakage characteristics. However, it also means that there will be uncertainty with regards to the true location and leakage characteristics for sections of the pipe where the leakage characteristics are realistic. Nonetheless, the measured leakage rate together with the estimated leak characteristics provided valuable information on the pipeline conditions, making it possible to rank the pipelines according to the severity of their conditions, for optimal allocation of maintenance resources. Through practical tests, the study shows that pressure testing is an effective, simple and low cost technique to assess leakage in bulk pipelines. It causes minimal interference to the pipe operation, requires little downtime and the data can be processed in minimal time.