Failure of water supply networks in selected Polish towns based on the field reliability tests
Introduction
In Poland reliability theory and engineering of water supply systems have been developed since the beginning of the 1970s, while theories related to the risk and safety of water supply systems have been developed since the mid-1990s. Due to the political situation the development of that theory is connected to works carried in the former USSR [5]. Opening to the world, which took place after political transformation accelerated significantly that development. One of the typical issues developed since then is the evaluation of reliability of a water distribution system. Reliability is most often considered in the aspect of necessity to provide the required quantity and pressure of water (hydraulic reliability) [3], [7], [13], [14], [16], [19], [20]. The issues related to reliability of supplying water with required quality are also developed [4], [9], [11], [12].
In order to objectify the evaluation of reliability of water supply for inhabitants and other recipients, it is extremely important to determine unique criteria of reliability. Suggestions in this reference can be found in the literature [6], [10], [17], [18], [19]. The criteria proposed in the last two works are used for practical evaluation of reliability of various water supply systems in operation in Poland. Operating reliability tests carried out at water supply networks operating on-line are of high practical importance, their results are reliability/unreliability indexes that facilitate evaluation of the technical condition of those networks.
In Poland in 2010 over 272.9 thousands km of water supply networks were in operation. That is almost three-times increase comparing to 1990. The growth of length of water supply networks for 1 year averages 9000 km, while, because of geo-economic conditions, most of that kind of investments is associated with the countryside (see Fig. 1).
These networks provide with water 33.4 mln people i.e. 87.5% of the whole population of Poland [2].
Material structure of water supply networks in Poland has been systematically changing since 1990. The direction of these changes indicates that in recent years polyethylene (PE) pipes and pipe fittings were widely used in building networks. Constant growth of ductile cast iron water supply networks is also observed, but to a smaller extent. The 2008 research indicates (Fig. 2) that despite intensive development and replacement of old pipelines with pipelines made of new materials, the material structure of the analyzed water supply networks still contains high proportion of traditional grey cast iron (36.9%) and steel (12.7%). There is also a significant percentage, due to operation of networks, of asbestos cement pipelines (4.4%) which for many years have been systematically replaced with pipelines made of new materials, such as PE and ductile cast iron. As a result, plastic pipelines constitute significant proportion of the material structure, with approx. 27.3% (PVC) and 15.1% (PE) of the length of the analysed water supply networks.
Together with development and replacement of water supply facilities other activities are being conducted/carried out with focus on reliability increase of performance of water supply networks: reduction of pressure, leakage detection, monitoring, constant increase of work standards for water treatment plant (WTP) and pumping stations.
The objective of this article is to present the results of all the activities, by showing an example of three selected water supply networks in a large city, a medium-sized city and a small city.
Section snippets
Methodology of research
The reliability research presented in this article encompassed number of failures of distribution systems in three cities in respective years, divided into main pipes, conduits and house connections. In 5-years research period there were the following failures identified: mechanical and corrosive perforation, transverse crack, pipe profile/side crack, sleeve crack, connections crack, pushing the seal, disappearance of seal, malfunction and damage of gate valves, unsealing of the pipes flange
The object of research
The analyses were carried out on water supply distribution systems from three cities in Poland. The period of research covered 5 years. The number of inhabitants of the analysed cities was respectively: 2 million, 350 thousands, 40 thousands. The cities were located in non-earthquake zone. The computational temperature were there −20 °C in winter and +30 °C in summer. The lengths of specific kinds of pipelines have been presented in Fig. 3. There were no significant changes of mains and conduits’
Tests results and discussion
Obtained values of failure rate are presented in Fig. 5.
Fig. 5 indicates, that, despite similar age and network material structure in those three considered cities significant values differences of calculated failure rates appear. Average values, from period of 2005 to 2010, of these rates are compared in Table 2.
Such significant values differences of failure rate results, as it seems, from few conditions: difference in composition of transferred water, correct operating process and quality of
Conclusions
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Poland is a country with a high failure rate of water supply networks. However, significant progress in this area in recent years should be noted.
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The research results indicate that, despite the similar structure of the material and age of investigated networks, the rates of failure intensity are significantly different in all three the examined cities.
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The lowest value of fault stream was noted in the middle size city. In both large and small cities its value was higher than average for the
Acknowledgements
Scientific work was financed from the measures of National Center of Research and Development as a development research Project No. N R14 0006 10: “Development of comprehensive methodology for the assessment of the reliability and safety of water supply to consumers” in the years 2010–2013.
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