Pipe Break Data Analysis in Emilia-Romagna, Italy

Pipe break data analysis in Emilia-Romagna,

Italy: afirs t step towards effective management of water distribution networks

V. Di Federico*, S. Mazzacane^ & G. Bizzanf *D.I.S.T.A.R.T. - Idraulica, Universita di Bologna, Italy

Dipartimento di Architettura, Universita di Ferrara, Italy

Abstract

As part of an effort to reorganize the water services in Italy, this study analyzes several urban water distribution networks in Regione Emilia-Romagna, in Northern Italy. The study focuses on breaks in pipes constituting the network during the years 1994-1997. First, a standard recording format was developed to collect and classify pipe break data and other information in networks with widely different structure and characteristics. Second, data were analyzed to determine the spatial and temporal distribution of breaks in space and time for each network; the yearly and seasonal mean break rates were evaluated for each material, to individuate significant trends in time and non-homogeneities in the break spatial distribution: the break rate was found to increase significantly during the summer in all networks examined. Furthermore, pipe break rates was found to depend inversely on diameter, confirming literature findings. Data analysis by material, tough hindered by the scarcity of data, evidenced widely different break rates; where present, nodular cast iron pipes exhibited the lowest break rate. As to other factors possibly influencing break rates, the study showed a weak positive correlation with precipitation, and no correlation with temperature or traffic levels. It was not possible to establish a quantitative correlation with pipe age because of the lack of data. The study indicated a necessity to standardize the procedures adopted to collect and classify data by the Agencies managing the service. The semi- quantitative correlations derived will prove useful in scheduling a timely substitution of the pipes in the water distribution network.

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Introduction

Cities all over Europe spend increasing sums of money for water network

rehabilitation. Today, the rationale behind rehabilitation expenditure decisions is unclear, and mostly based on a reactive approach. Management planning methods (pro-active approach) need to be developed for effective decision making. In Italy, a major effort is being undertaken in this direction as required by a recent law, the so-called "Legge Galli" [1] which introduced new concepts

on integrated water management; according to it, the twenty Italian Regions have to: - organize an "integrated water management"; divide their own territory in "optimal basins";

separate ownership from management, transferring the latter to the private sector. "Integrated water management" means unitary management of the service for the entire water cycle: water supply, transmission, and distribution, sewer

systems and wastewater treatment plants. In order to supply these services, it is necessary to subdivide the regional territory into sub-areas, roughly coincident with an hydrographic basin, whose dimensions are much larger than those of a present typical area managed by a municipality. Regions are entrusted with the responsibility of designing boundaries of these areas, and establishing how the

municipalities should cooperate together. The law also establishes the principle that the ownership of the water services (all the concurring municipalities together) should be separated from the management. The owner assigns qualitative and quantitative objectives in terms of efficiency and reliability levels, and control policies. Revenues will cover all costs connected to the

service management. Consequently, technical, financial, and quality standard indicators should be established, in order to compare management performance. A key factor in the fulfillment of the law requirements is the reduction of water losses in distribution networks; this goal may be reached following two different procedures:

- hidden leaks detection and reduction; - networks reliability analysis targeted to prevent breaks and, consequently, losses. A definition of reliability for a water distribution system is not

straightforward nor unique: nevertheless analysis of breaks in pipes constituting the network is an essential step towards reliability evaluation. Several models with various degrees of complexity have been proposed to determine the optimal pipe replacement rate and break probability [2-7]. However, the minimum database needed as an input to these models exceeds the data presently available to most Italian agencies.

To gather the necessary data, the "Servizio Analisi e Pianificazione Ambientale" (Environmental Analysis and Planning Division) of Regione Emilia-Romagna, in Northern Italy, has entrusted the study of its urban water distribution networks to Consorzio Ferrara Ricerche, in connection with Bologna and Ferrara University. The first part of the study, focusing on breaks in pipes

Risk A nalysis II 219

constituting the network during the years 1994-1997, is reported here and, in more detail, in the book by Di Federico et al. [8].

Data collection methodology

Since each Agency managing the network operates differently, available data for each network were subdivided into three blocks: - information about the managing Agency;

- general data concerning the water distribution network; - data about breaks. The following Agencies participated to the study: ACOSEA in Ferrara, AGAC in Reggio Emilia, AMI in Imola (BO), AREA in Ravenna, ASM in

Piacenza, SEABO in Bologna, and CADF in Codigoro (Ferrara); results of data processing about the latter are not yet available. In particular, break data were acquired for the most part consulting electronic databases and archives made available by the managing Agency; in other instances, individual break records were available only in paper format. In

the latter case, a new electronic database was developed, and complemented with information derived from networks maps. A preliminary analysis of the database showed that several events are due to external causes and therefore cannot be considered of interest to our investigation. To select relevant data for further analysis, we adopted two main criteria. First, we excluded "no-excavation" jobs,

such as those connected with reinstatement of the road and meter. Second, we classified remaining breaks as i) due to external causes; ii) imputable to pipes intrinsic reliability. In case i), no diggings were necessary per se: the break happened either when the pipe was pulled out of the ground, or when exposed.

These breaks are mainly due to excavations close to the pipe, due to contacts with other utilities (electric, telephone, gas); they are frequent, but not related to pipes reliability, and were therefore excluded. Data belonging to the resulting subset were analyzed, and classified either as house connection breaks and main network breaks; a preliminary investigation showed that the break rate was

higher in house connection than in the rest of the network. A possible explanation for the high incidence of breaks in house connections include: small diameter (small pipes seem more amenable to breaks [9, 10]) and the low depth which increases the likelihood of interfering with other underground services. We omitted any further analysis of house connections breaks, and focused on

breaks in the distribution network: of these, only those pertaining to urban areas are discussed here.

Characteristics of the water distribution networks

A total of seven distribution networks were examined, though data from Codigoro are not yet available. Table 1 shows the total network length L and population served P, together with the index PIL. The distribution networks examined vary in length from 190 Km to 649 Km, and serve from 60,000 to 383,000 people. Overall they include 2,631 Km of pipelines serving 1,003,000

220 Risk Analysis 11

inhabitants. The ratio PIL varies from a minimum of 115 (Imola) to a maximum of624(Ferrara).

Table 1: Network length and population served

CITY Length (km) (L) Population (x 1000) (P) P/L BOLOGNA 649 383 590 FERRARA 391 244 624 IMOLA 523 60 115

PIACENZA 287 99 345 RAVENNA 190 87 458 REGGIO E. 591 130 220 TOTAL/MEAN 2,631 1,003 381

Table 2 shows an inventory of the urban distribution network piping, where STE

= steel, AC = asbestos cement, GCI = gray cast iron, NCI = nodular cast iron, PO = polythene, PVC = PVC, O = other, and UNK = unknown. The materials constituting the pipelines vary widely among the networks, depending on the policy followed by the managing Agency in the past decades. Overall, more than

half (51%) of the pipelines are made of asbestos cement, while gray cast iron, nodular cast iron, polythene, and PVC account approximately for 10% each; steel is not frequent (3.8%).

Table 2: Composition of distribution networks

CITY STE AC GCI NCI PO PVC 0 UNK TOTAL BOLOGNA 7.24 7.90 3.01 « 11.57 0.20 - 0.08 100 FERRARA 5.83 54.80 3.31 36.04 - 0.01 - 0.01 100 IMOLA 0.35 39.44 6.14 - 31.05 22.98 0.04 - 100 PIACENZA - 0.28 27.64 72.00 0.08 - - - 100 RAVENNA 1.73 65.12 30.90 - 2.23 - 0.02 - 100

REGGIO E. 4.05 50.23 3.05 - 13.08 17.34 - 12.26 100 MEAN 3.8 51.2 8.4 13.2 12.1 8.5 0.0 2.8 100

Analysis of break events

This study focuses on breaks in pipes during the period 1995-1997; older data are difficult to obtain, since maintenance events were recorded in paper format prior to 1995 and a computer database is not available. Available data were analyzed according to the criteria outlined in the

previous paragraph; the remaining data subset consisted of 1533 events. The record corresponding to each event included the date, the place, the material and the diameter of the pipeline interested by the break, plus additional information. Results of the analysis included: - location of breaks on city maps;

Risk Analysis II 221

- computation of the number of breaks for each material; - computation of the break rate for each material;

- examination of the trends of breaks in time; - examination of the correlation between break rate and pipes diameter; - correlation between break rate, temperature, rainfall intensity and traffic

levels. Results are reported in full in Di Federico et al. [8]: here their main conclusions are summarized. The average break rate for each network, computed by dividing the total number of pipe breaks by the length of the distribution network, is shown in

Table 3 for the period 1995-1997 (1994-1997 for Reggio Emilia).

Table 3: Average pipe break rate in the period 1994-1997

PIPE BREAK RATE CITY 1994 1995 1996 1997 Mean BOLOGNA 0.174 0.145 0.185 0.168 FERRARA 0.220 0.315 0.348 0.294 IMOLA 0.061 0.142 0.176 0.159 PIACENZA 0.049 0.091 0.049 0.063 RAVENNA 0.132 0.237 0.237 0.202 REGGIO E. 0.281 0.168 0.146 0.152 0.187 MEAN 0.148 0.179 0.191 0.183

The mean break rate over the considered time span is not too different for the cities considered, and varies between 0.159 to 0.294 breaks per year for every kilometer of pipe; Piacenza is an exception in that its break rate is much lower (0.063 breaks/yr/km); however, this statistic is based on a very limited number of total breaks. Data also suggest that the yearly break rate tends to increase in Ravenna, Imola and Ferrara, to remain constant in Bologna and Piacenza, and to decrease in Reggio Emilia. The latter tendency is significant from 1994 to 1995, and, to a lesser degree, from 1995 to 1996. Based on models predicting an increase in breaks with pipes age [4,6, 11], one would expect the number of breaks/year in Reggio Emilia to increase or, at best, remain constant, as verified in all other cities examined. The unexpected effect might be due to the smallness of the data set, or to massive replacement of old pipes undertaken during the period 1994- 1995. However, a detailed inspection of data shows that pipes replaced during 1994 accounted for a total length of 2022 m (0.3% of total network length);

furthermore, maintenance operations undertaken did not affect significantly the network average age; this leaves the sharp decrease in break rates from 1994 to 1995 still unexplained. A possible explanation is as follows [12]: beginning in 1993, the network was subdivided into 25 smaller hydraulic units (districts), introducing 120 new valve gates. This was done to prevent and control leaks more easily. However, it also affected the hydraulic conditions of the network

222 Risk Analvsis II

and, in particular, the head distribution. Qualitatively, since additional sources of dissipation were introduced, the head in the network during the day was, in a general sense, lowered, as suggested by a few partial registrations of head in 1993-1994 while the network division was under way. Unfortunately, average head data in pipes before and after districtualization are not available. We

suggest that the reduction in breaks from 1994 to 1995 and, to a lesser degree, 1996 is imputable to values of head generally lower and thus, to a minor incidence of hydraulic transients, much like the higher break rate in summer is related to higher values of head. To support this conclusion, we also note

hydraulic transients are, among others, caused by hydraulic maneuvers; in 1994, instruction of maintenance squads on how to operate valves to connect/disconnect districts had just begun; it is therefore probable that a higher number of improper maneuvers was executed in 1994 than in 1995 or 1996. As a consequence, the 1994 break rate may represent an anomaly and that 1995 or

1996 values may be more representative of the real failure rates; this is supported by the fact that break rates seem to stabilize from 1995 to 1996. An additional factor that may have contributed to the 1994 anomaly was a hidden leaks detection program which was conducted in 1994, which contributed to increase the number of hydraulic maneuvers. Unfortunately, a comparison with break

rates prior to 1994, when the division of the network into districts was not yet in place, is not feasible. An analysis of the distribution of breaks during the year showed that break rates increase significantly during the summer in all the networks examined; this

is in contrast with experience in the U.S., where a major portion of breaks happens during the winter [3]. Values of mean break rates for different materials during years 1995 to 1997 are reported in Table 4 for each network.

Table 4: Pipe break rate by material

CITY STE AC GCI NCI PO PVC BOLOGNA 0.020 0.157 0.324 - - - FERRARA 0.452 0.160 0.424 0.064 - - IMOLA - 0.068 0.166 - 0.261 0.019 PIACENZA - - 0.229 0.000 - -

RAVENNA - 0.170 0.222 - - - REGGIO E. 0.000 0.253 0.876 - 0.055 0.102 MEAN 0.157 0.173 0.373 0.032 0.158 0.061

The break rate is found to be highest in the asbestos cement and gray cast

iron pipes, lowest in the ductile cast iron ones. The average values shown in Table 4 by material are of the order of those reported in the literature [3,9, 13]; they show that the break rate strongly depends on the material; in turn, materials showing the highest break rate are the oldest (GCI and AC). In fact, the average pipe age is 1-3 years for PE, 4-15 years for PVC, 5-10 years for NCI, 10-35 years for STE, 16-35 years for AC, and 36-115 years for GCI. It is unclear

Risk Analysis II 223 whether the increment in break rate is due to the difference in material or to age.

If the break rate increase was independent from material, we could hypothesize an increase in failure rate with time. However, at this stage there are simply not enough information on age for such an analysis. We also tried to determine how the pipe break rate is influenced by pipe diameter. The data seem to show a decrease in the break rate with diameter; in some cases, regression equations with a negative power law relationship were found to interpret well this tendency. Finally, as to other factors possibly influencing break rates, the study shows a weak positive correlation with precipitation and no correlation with temperature or traffic levels.

Summary and conclusions

Under the present legislation, the Italian water distribution system is required to achieve a better management efficiency. For urban distribution system, reduction of water losses is a key issue in reducing costs and improving the serviceability. To achieve this goal, we focused on the analysis of breaks in pipes in a number of water distribution networks in Emilia-Romagna, including several main cities. Our major conclusions are: - There are not enough data to employ existing methods for reliability evaluation to Italian water distribution networks, since available databases on breaks are of limited size;

- The composition by material of the networks analyzed varies widely; asbestos cement constitutes more than half of the total network length examined; - The mean break rate in different networks varies between 0.159 to 0.294

breaks/year/km, except in one instance; further, the break rate is inversely proportional to pipe diameter, i.e. smaller pipes tend to break more often; different materials have widely different break rates, caused either by an age difference or their intrinsic characteristics; due to insufficient information, we were unable to quantify the impact of age;

- Temperature, rainfall and traffic levels were not major determinant of break rate; a significant correlation was found between the monthly number of breaks and head. This is probably caused by an increased impact of hydraulic transients when average head in the network is highest;

Break rates tend to increase or to remain constant, with the exception of Reggio Emilia, where the its decrease is probably due to a different network scheme; further analysis based on a more extended database is needed to fully validate these predictions. Analysis of more recent break data is under way.

Acknowledgements

The authors would like to thank Regione Emilia-Romagna, Servizio Analisi e Pianificazione Ambientale, for providing financial support for this research and

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ACOSEA, AGAC, AMI, AREA, ASM, CADF, and SEABO for their cooperation. The authors hereby certify that they equally contributed to the theoretical elaboration and the writing of this paper.

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