Assessment of the failure rate of water supply system in terms of

Dawid SZPAK*, Barbara TCHÓRZEWSKA–CIEŚLAK – Department of Water Supply and Sewage
Systems, Faculty of Cyvil and Environmental Engineering, Rzeszów University of Technology,
Rzeszów, Poland
Please cite as: CHEMIK 2014, 68, 10, 862–867
Introduction
Collective water supply system (CWSS) belongs to the so called
critical infrastructure according to the Act [10] on crisis management.
Protection of critical infrastructure involves providing continuity of
operation and quick recovery in case of failure or other adverse events.
The information on methods of establishing and planning critical
infrastructure protection is presented in the Directive [3].
Collective water supply system shall have safety level understood
as system resilience to hazards required. CWSS comprises [11]:
• water supply subsystem
• water intake subsystem
• water treatment subsystem
• water transfer subsystem
• water accumulation subsystem
• water distribution subsystem
• water supply network
• water supply facilities.
Water supply network is the most susceptible to damage, while
the water accumulation subsystem exhibits the lowest risk of failure
[2]. For the correct evaluation of adverse event, it is necessary to fully
characterize it taking into account inter alia, failure cause, failure
duration and its effects [12].
The main aim of the paper is to analyse and evaluate the risk of
failure of water supply system in terms of CWSS operation safety. The
analysis was carried out for the case of CWSS in the town of Jasło.
The largest increase in the network length was 11.4 km in years
2012–2013 for the distribution network. Almost 50% share of PE
pipes in total length of water supply network for each analysed year
and approx. 89% share of plastics in total network length in 2013 are
definitely worth noting.
Figure 1 shows age of water supply pipes of the town of Jasło in
years 2009–2013.
Description of CWSS in the town of Jasło
Jasło is a county-town in south-eastern Poland in Podkarpackie
Voivodeship. In 2012, the town area was 36.52 km2, while the number
of inhabitants was 36,709 [7]. The town of Jasło is supplied in water
from main surface intake of capacity of 17,280 m3/d and reserve
groundwater intake of capacity of 348 m3/d. There are two distribution
final tanks of volume 900 m3 each and two initial tanks of total volume
of 5,000 m3. Water supply network is of mixed configuration. There are
five local water pumping stations for increasing water pressure in the
network. Material structure of the distribution network of the town of
Jasło in years 2009–2013 is presented in Table 1.
Analysis and assessment of water supply network failure rate
Assessment of technical conditions of water supply network was
carried out based on the damage intensity according to the formula [5]:
(1)
Table 1
Material structure of the distribution network of the town of Jasło
in years 2009–2013
Length of water supply network, km
Year
Grey cast iron
Steel
AC
PVC
PE
Total
2009
31.8
21.2
0.8
13.2
65.4
132.4
Fig. 1. Age of water supply pipes of the town of Jasło
in years 2009 – 2013
The following changes related to the network development
are also very noticeable: the decrease in pipe length of exploitation
period exceeding 25 years and significant increase of amount of pipes
under 10 years old.
where:
n (Δt) – number of damages in time period Δt
L – length of examined pipes in time period Δt, km
Δt – considered time period, years.
Damage intensity was determined for distribution pipes and
household connections. In Jasło typical water mains are not classified.
Damage intensity determined using formula (1) is presented in Table 2.
Table 2
Damage intensity λ no. of dam./km·a for distribution pipes and
household connections in years 2009–2013
Damage intensity λ no. of dam./km·a
Year
Distribution
Pipes
Household
connections
Total network
2010
8.8
5.4
0.8
55.5
63.4
133.9
2011
6.7
18.8
0.8
44.6
67.5
138.4
2009
0.28
0.23
0.27
2012
6.7
18.8
0.8
44.6
69.7
140.6
2010
0.20
0.47
0.28
2013
6.4
9.8
0.8
52.5
82.5
152.0
Corresponding author:
Dawid SZPAK – M.Sc., e-mail: [email protected]
nr 10/2014 • tom 68
2011
0.27
0.30
0.28
2012
0.27
0.50
0.34
2013
0.25
0.25
0.25
• 865
XV Conference Environmental
Assessment of the failure rate of water supply system
in terms of safety of critical infrastructure
XV Conference Environmental
Obtained results were compared with limit values for damage
intensity for particular types of pipes presented in the articles [1, 8, 9]:
• distribution pipes: λ = 0.5 no. of dam./km·a
• household connections: λ = 1.0 no. of dam./km·a
The carried out analysis shows that failure rate of water supply pipes
of the town of Jasło meets above requirements. The damage intensity
of distribution pipes had the highest value in 2009 λ = 0.28 no. of dam./
km·a, i.e. much lower than recommended value λ = 0.5 no. of dam./
km·a. Similarly, damage intensity of household connections is much
lower than recommended value of λ = 1.0 no. of dam./km·a and was
the highest in 2012 (λ = 0.5 no. of dam./km·a). It is visible that pipes of
household connections have on average higher damage intensity than
distribution pipes. This is in line with previously conducted studies
on failure rate of water supply networks [4]. Table 3 presents basic
statistics for average damage intensity in years 2009 – 2013.
Table 3
Basic statistics for average damage intensity in years 2009–2013
Type of
pipes
Average
λ,
Quartile
Stannumber no. of dam./km·a
Average
Me- dard
of failures
network
dian deviaper year,
length, km
lower upper
tion
number of λmin λav λmax
(25%) (25%)
failures/a
Distribution
pipes
139.46
35.6
0.20 0.25 0.28 0.27 0.032
0.25
0.27
Household
connections
60
21
0.23 0.35 0.50 0.30 0.126
0.25
0.47
Damage intensity depending on material type used for construction
of water supply network is presented in Figure 2.
Water supply in emergency situations
In case of emergency situation (no water supply to the town), Jasło
will be supplied using alternative water intakes:
• Huta Szkła, Śniadeckich Street 19 – 228 m3/d
• Jasan Sp. z o.o., Szajnochy Street – 576 m3/d
• Zakład Masarski „TRIO” S.C., Lwowska Street 12 – 156 m3/d
• public wells – 1,358.4 m3/d
• fire wells (shortest possible time of providing the inhabitants with
water is 7 days) – 2,340 m3/d
• approx. 1,000 private wells in suburban areas
In emergency situations there are four types of specific water
demands [6]:
• water quantity related to human physiology – qp = 2.5 dm3/inh. d
• minimum water quantity for period of several days – qm =
7.5 dm3/inh. d
• essential water quantity for period of several weeks – qe =
15 dm3/inh. d
• required water quantity in emergency situation – qr = 30 dm3/inh. d.
Average daily water demand in 2013 was Qav = 5630.78 m3/d. The
CWSS of the town of Jasło is used by approx. 34,500 inhabitants. This
number was a base for determination of water demand in emergency
situations:
• water demand for physiological purposes
(2)
• minimum water demand
(3)
• essential water demand
(4)
• required water demand
(5)
The determined amount of water may be supplied to inhabitants
using 1.5 dm3 bottles, 5 dm3 bottles and water tankers of 8 m3 capacity
making three courses per day. (Table 4) [6].
Table 4
Determination of number of bottles and water tankers needed for
providing water for inhabitants in emergency situations [6]
Water
demand, m3/d
Number of 1.5
dm3 bottles
Number of 5
dm3 bottles
Number of water
tanks of capacity
3 · 8 m3
Qp
86.25
57,500
17,250
4
Qm
258.75
172,500
51,750
11
Qe
517.50
345,000
103,500
22
Qr
1035.00
690,000
207,000
43
Fig. 2. Damage intensity depending on material type used for
construction of water supply network in years 2009–2013
The lowest damage intensity was found for PVC pipes – λmax=0.15
no. of dam/km·a ­– and PE pipes – λmax=0.27 no. of dam/km·a. High
values of damage intensity for pipes made of grey cast iron, steel and
AC (for 2011) are hard to miss.
The obtained values of damage intensities were compared with
average damage intensities calculated based on the long-term studies
presented in [5]. Average damage intensity is:
• for grey iron cast: λ = 0.48 no. of dam./km·a
• for steel: λ = 0.55 no. of dam./km·a
• for AC: λ = 0.37 no. of dam./km·a
• for PVC: λ = 0.15 no. of dam./km·a
• for PE: λ = 0.32 no. of dam./km·a
Damage intensities for PVC and PE pipes are lower than for
data presented in [5]. Higher values of damage intensity have been
designated for pipes made of grey cast iron and steel and, in 2011,
this was also observed for AC pipes. Based on [6], it was assumed that
damage intensity equal to λ = 1 no. of dam./km , qualifies pipes for
replacement (in accordance with the European standards).
866 •
The conducted assessment showed that emergency groundwater
intakes fully cover (100%) water demand and there is no need
to support water supply from external sources.
Summary
Collective water supply system belongs to the critical infrastructure.
Due to that, actions of water supply companies shall focus on ensuring
safety of the CWSS, preparation of crisis management plans and
mitigating effects of potential emergency situations.
The constant increase in the length of the water supply distribution
network is observed. Pipes made of traditional materials, such as grey
cast iron, has been replaced with plastic pipes. Water supply network
of the town of Jasło in 2013 was composed in 89% of PVC and PE
nr 10/2014 • tom 68
7. Rak J., Sypień Ł.: Analiza strat wody w wodociągu miasta Jasła.
Czasopismo Inżynierii Lądowej, Środowiska i Architektury. Oficyna
Wydawnicza Politechniki Rzeszowskiej. t. XXX, z. 60 (3/13), lipiec –
wrzesień 2013, 5–18.
8. Rak J., Tchórzewska–Cieślak B.: Awaryjność sieci wodociągowych
w głównych miastach Doliny Sanu. III Konferencja Naukowo – Techniczna
Błękitny San, Dubiecko 21–22 IV 2006.
9. Studziński A., Pietrucha – Urbanik K.: Awaryjność sieci wodociągowej
Tarnowa. Gaz, woda i technika sanitarna. 2012, 10, 464–466.
10. Ustawa z dnia 26 kwietnia 2007 r. o zarządzaniu kryzysowym (Dz. U.
z 2007 r. Nr 89, poz. 590) oraz zmiana z 2010 r., Dz.U.240 poz. 1600.
11. Wieczysty A., Rak J.: Niezawodność systemów zaopatrzenia w wodę
w aspekcie wymagań jakościowych. Ochrona Środowiska. 1995.
1(56). 5–10.
12. Zimoch I.: Niezawodnościowa interpretacja awaryjności podsystemu dystrybucji
wody. Czasopismo Techniczne. Środowisko. Wydawnictwo Politechniki
Krakowskiej im. Tadeusz Kościuszki, R. 108, 2011, z. 1-Ś, 211–223.
*Dawid SZPAK – M.Sc., has graduated from the Faculty of Civil and
Environmental Engineering at Rzeszów University of Technology (2013). He
currently works at the Department of Water Supply and Sewage Systems,
Rzeszów University of Technology. Scientific interests: reliability in collective
water supply systems.
e-mail: [email protected], phone: +48 17 8651427
Literature
1. Bergel T.: Awaryjność sieci wodociągowych małych wodociągów grupowych w Polsce.
Gaz, woda i technika sanitarna. 2012, 12, 536–538.
2. Denczew S.: Niezawodność, bezpieczeństwo i ryzyko systemów eksploatacji
wodociągów w aspekcie infrastruktury krytycznej. Eksploatacja i niezawodność.
2007, 2, 15–21.
3. Dyrektywa Rady 2008/114/WE z dnia 8 grudnia 2008 r. w sprawie rozpoznawania
i wyznaczania europejskiej infrastruktury krytycznej oraz oceny potrzeb
w zakresie poprawy jej ochrony.
4. Kwietniewski M.: Awaryjność infrastruktury wodociągowej i kanalizacyjnej w Polsce
w świetle badań eksploatacyjnych. XXV Konferencja Naukowo-Techniczna,
Międzyzdroje 24–27 maja 2011.
5. Kwietniewski M., Rak J.: Niezawodność infrastruktury wodociągowej i kanalizacyjnej
w Polsce. Polska Akademia Nauk. Komitet Inżynierii Lądowej i Wodnej, Instytut
Podstawowych Problemów Techniki, Warszawa 2010, 37–81.
6. Rak J. i in.: Niezawodność i bezpieczeństwo systemów zbiorowego zaopatrzenia w wodę.
Oficyna Wydawnicza Politechniki Rzeszowskiej. Rzeszów 2012, 49–59, 159–163.
Barbara TCHÓRZEWSKA–CIEŚLAK – Ph.D., D.Sc., Eng., Ass. prof., has
graduated from the Faculty of Civil and Environmental Engineering at
Rzeszów University of Technology (1997). She has received her Ph.D.
from the Faculty of Environmental Engineering, Cracow University
of Technology (2002). She has received her D.Sc. from the Faculty of
Environmental Engineering, Wrocław University of Technology (2012).
She currently works at the Department of Water Supply and Sewage
Systems, Rzeszów University of Technology. Scientific interests: analysis
and assessment methods of reliability and safety in collective water
supply systems, balneotechnology. She has authored 3 monographs,
authored or co-authored 72 scientific publications (scored) and 28
publications published in conference materials.
e-mail: [email protected], phone: +48 17 8651435
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XV Conference Environmental
pipes, which is in line with worldwide trend to use thermoplastics and
nodular cast iron for construction of water supply networks, which
significantly decreases the failure rate.
Average values of damage intensity are of order λ = 0.25 no. of
dam./km·a for distribution pipes and λ = 0.35 no. of dam./km·a for
household connections and are lower than limits equal to λ = 0.5 no.
of dam./km·a and λ = 1.0 no. of dam./km·a, respectively. This
indicates good technical conditions of water supply network of the
town of Jasło.
The lowest damage intensity was found for PVC pipes and PE
pipes – λav = 0.07 no. of dam./km·a and λav = 0.21 no. of dam./km·a,
respectively. These values are lower than ones from the literature
data, which were obtained through long-term studies of operation
of Polish water supply networks. High damage intensity for cast
iron pipes λav = 1.77 no. of dam./km·a and AC pipes λ = 2.5 no.
of dam./km·a in 2011 (with only two failures) based on European
standards qualifies these pipes (limit λ= 1 no. of dam./km·a) for
replacement or renovation. High damage intensity for steel pipes is
also noticeable, however, it has not exceeded limit of λ = 1 no. of
dam./km·a, with the exception of 2010.
In case of emergency situation, the town of Jasło can fully cover
required water demand from its own emergency groundwater
intakes.