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Survey of water main failures in the United States and Canada (1)

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During 2011, Utah State University conducted a basic survey of utilities across the United States and Canada to obtain data on water main failures of municipal and private water supply systems. Surveys were mailed to a total of 1,051 US and Canadian water utilities in May and June of 2011. – PowerPoint PPT presentation

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Title: Survey of water main failures in the United States and Canada (1)


1
utility operations
?
Steven Folkman, John Rice, ammon So Ren Son,
and nathan BRaithwaite
Survey of water main failures in the United
States and canada
DCanadian water utilities in May and June of
2011. Those that
uring 2011, Utah State University conducted a
basic survey
RUt eS l S oF a 2011 SURveY oF UtilitieS in the
United StateS and canada PRovideS inFoRmation
on wateR main FailUReS in mUniciPal and PRivate
wateR SUPPlY SYStemS.
of utilities across the United States and Canada
to obtain data
on water main failures of municipal and private
water supply
systems. Surveys were mailed to a total of 1,051
US and
responded to the basic survey were also invited
to participate in a more
detailed survey. A total of 188 utilities
responded and completed the basic survey, with
47 also responding to a detailed survey. A total
of 117,603 mi of pipe were represented in the
basic survey and 32,130 mi in the detailed
survey. This article documents some of the
results from both surveys. One of the primary
goals of this survey was to obtain data on
current pipe inventories and failure rates of
different pipe materials during a previous
12-month period. Most of the responses to the
survey were received in the middle of 2011
thus, the survey estimates behavior during the
2010 and 2011 calendar years. The detailed survey
allowed collection of a wider variety of data
relating to operating parameters, installation
practices, and pipe material preferences.
70 OCTOBER 2012 JOURNAL AWWA 10410 FOLKMAN
ET AL
2
  • Region 820 (4)
  • Region 912 (5)
  • No responses were obtained from the Canadian
    provinces of New Brunswick, Newfoundland, Nova
    Scotia, Prince Edward Island, or Quebec. Figure
    1 shows the miles of water main pipe that were
    reported in the basic and detailed surveys
    according to region.

water main pipe represented by those utilities.
The trend line and equation are a best fit to
the data with a zero intercept. The slope of
this line indicates that on average there are
264 people served for each mile of water main
installed.
  • SURVEY REGIONS
  • To show participation as a func- tion of
    geography, the areas covered by the basic survey
    were broken down into nine regions as shown in
    the map on page 71. The number of respondents to
    the basic survey are listed, followed by the
    number of respondents to the detailed survey in
    parentheses.
  • Region 119 (7)
  • Region 220 (4)
  • Region 326 (5)
  • Region 422 (6)
  • Region 518 (3)
  • Region 628 (11)
  • Region 723 (2)

SURVEY SAMPLE SIZE The total length of water main
pipe reported by the 188 survey par- ticipants
was 117,603 mi (the survey did not include sewer
or force mains). In 2007 the US Environmen- tal
Protection Agency (USEPA) reported that there
are approxi- mately 880,000 mi of distribution
MILES OF PIPE VERSUS POPULATION Figure 2 shows
the relationship between the population served
by the utilities participating in the basic
survey and the number of miles of
BC AB
MB SK
QC
NL PEI
Region 9
AK
ON
NB
WA Region 1 OR
NS
MT
ME
ND
VT NH MA RI CT NJ DE
MN
ID
WI
SD
NY
WY
MI
PA Region 8
Region 6 IL IN
NE
IA
Region 3
NV
OH
Region 2
Region 4
UT
WV
CO
HI
VA
KS
CA
MO
KY TN
NC
MD
OK
AZ
NM
AR
SC
DC
Region 5
GA Region 7
AL
MS
LA
TX
FL
This map illustrates the regions as they were
defined to report the basic and detailed survey
results.
FOLKMAN ET AL 10410 JOURNAL AWWA
OCTOBER 2012 71
3
pipe in the United States (USEPA, 2007). The
following year, a second report (Royer, 2008)
estimated the
survey would then represent approx- imately 10
of the installed water main pipe in the United
States. Thus
quantified the size of a utility based on the
number of miles of water main pipe installed.
Four categories were established according to
miles of pipe small (up to 500 mi), medium
(5001,000 mi), large (1,0003,000 mi), and very
large (more than 3,000 mi). Each survey
participant was allocated to one of the
categories. Figure 3 shows the distribution of
total miles according to these categories.
a primary goal of this survey was to obtain
data on current pipe inventories and failure
rates of different pipe materials during a
previous 12-month period.
amount of installed water main pipe in the
United States to be more than 1 million mi. The
current population of the United States is 312
million (US Census, 2011). Using the esti- mate
from the previous section of 264 people served
per mile of water main, the length of water
mains can be estimated to be 1.18 million mi
(312 million people/264 people/ mile). With
the use of this last esti- mate, the total
length of pipe in the
survey sample size is significant and should
provide reliable results. The Canadian provinces
comprised 8,423 mi of pipe in this survey, or
7.4 of the total.
PIPE MATERIALS Many pipe products have evolved
over time, and most of these could be broken
down into subcategories on the basis of
processing and sur- face treatments. These
changes, along with new installation tech-
niques, should affect the life expec- tancy of
the pipe. The basic survey was intended to be
relatively simple to complete in order to
encourage wide participation. Most utilities
have limited records as to which spe- cific pipe
materials were installed decades ago. Therefore,
subcatego- ries of material types were not
tracked in the survey. The results reported in
this article represent generic pipe material
performance, but may not represent a specific
product on the market today. The distribution of
pipe materials based on miles of pipe is shown in
Figure 4. Pipe material distribution as a
percentage of the total length for both the
basic and detailed sur- veys is shown in Figure
5. The detailed survey had a smaller num- ber
of respondents but still gave a similar material
distribution. The other category in Figures 4
and 5 includes materials such as high- density
polyethylene, galvanized steel, and copper.
Eighty percent of the installed water mains are
a combination of cast-iron at 28, ductile-iron
at 28, and polyvinyl chloride (PVC) pipe at
23. The amount of concrete pressure pipe
(CPP), steel, and asbestoscement (AC) material
types were also reported. The length of
high-den- sity polyethylene pipe reported rep-
PARTICIPANTS CLASSIFIED IN FOUR CATEGORIES The
average utility surveyed had 626 mi of water
main, with the largest having 4,468 mi and the
smallest having 2 mi. This survey
FIGURE 1
Total miles of pipe by region responding to the
basic and detailed surveys
Basic survey
25,000
20,000
Pipemi
15,000
10,000
5,000
0
5 Region
1
2
3
4
6
7
8
9
Detailed survey
8,000
6,000
Pipemi
4,000
2,000
0
5 Region
1
2
3
4
6
7
8
9
72 OCTOBER 2012 JOURNAL AWWA 10410 FOLKMAN
ET AL
4
resented only 0.14 of the total and thus was
not tracked as a sepa- rate group. Figure 6
shows the regional distri- bution of pipe
material type as a percentage of the total
length of pip- ing in that region. Significant
differ- ences can be seen in the type of pipe
material used in the regions. Cast and ductile
iron represent approxi- mately 90 of the pipe
in regions 6 and 8. PVC has a dominant role in
region 9 and is a significant player in regions
25, and 7. Pipe age and diameter. The detailed
survey asked respondents to provide the age
distribution of installed pipe. Four age groups
were provided 010 years, 1020 years, 2050
years, and more than 50 years. Fig- ure 7, which
lists the percentage of water main length that
fits in each age category, indicates that
approxi- mately 43 of installed pipes are in
the 2050-year age category and 22 are more
than 50 years old.
Respondents were also asked to break down the
fraction of total installed pipe length by five
pipe-diam- eter categories. Figure 8, which
shows the percentage of water mains that fit
into each size range, indicates that
point in their systems during a typical day. The
survey indicated that approximately 83 of
respondents are able to limit pressure
fluctuations to less than 20 psi, 11 had
pressure fluctuations between 20 and 40 psi,
the total miles of pipe covered by this survey
is almost 10 of that in use in the United
States.
approximately 66 of the installed pipe is 8 in.
or less in diameter. Delivery pressure. On the
basis of results received in the detailed
survey, the average delivery pressure was
determined to be 77 psi. The range of values
reported for average delivery pressure was
45150 psi. Respon- dents were asked to select
one of three ranges provided in the detailed
survey to indicate how much the water pressure
fluctuates at any given
and 6 have pressure fluctuations in excess of
40 psi.
PIPE FAILURE Most common failure mode, mate-
rial, and age. The detailed survey asked the
respondents to identify the most common water
main failure mode by selecting from one of the
following categories circumferential crack,
corrosion (pits or holes), lon- gitudinal crack,
leakage at joints,
FIGURE 2
Population served relative to total pipeline
miles from the basic survey
1,400,000
y 263.78x R 2 0.8014
1,200,000 1,000,000 800,000 600,000 400,00
0
Population
200,000
0
0
1,000
2,000
3,000
4,000
5,000
Pipemi
FOLKMAN ET AL 10410 JOURNAL AWWA
OCTOBER 2012 73
5
fatigue, or other. Figure 9 shows that
circumferential cracks are the most common mode
of failure, followed by corrosion. The detailed
survey also asked respondents to identify which
pipe material failed most often. Figure 10 shows
that slightly more than 55 of respondents iden-
tified cast iron as the pipe material that
failed most often (likely because it is one of
the two most commonly used pipe materials and on
average is the oldest pipe material in use),
followed by AC at 17. Respon- dents also
reported that the typical age of a failing water
main was 47 years, with a range of values from
2086 years. The survey also asked what the
respondents believed the expected life should be
for newly installed pipe. Respondents expected
new pipe to have an average life span of 79
years, with responses ranging from 30 to 200
years. Computing failure rates. The basic survey
asked respondents to consider a water main
failure as one in which leakage was detected and
repairs were made. However, they were asked not
to report failures caused by joint leakage,
construction dam- age, or tapping of service
lines. The goal of the survey was only to exam-
ine the performance of properly installed
pipe. Utilities reported the number of failures
over a recent 12-month period according to pipe
material and the installed length of pipe mate-
rial. The failure rate was computed by dividing
the total number of fail- ures from all
utilities for a particular pipe material by the
total length of that pipe material. For example,
the survey reported a total of 12,963 failures
of water mains during a recent 12-month period
for all pipe materials. The total installed
water main length from the survey was 117, 603
miles (or 1,176.03 hun- dreds of miles). Thus
the overall fail- ure rate is 12,963/1,176.03
11.0 failures/(100 miles)/year. Figure 11 shows
the failure rate at each utility for all pipe
materials and indicates that utilities can
experience widely
TABLE 1
Summary of failure data over a 12-month period
Pipe Material Lengthmi Number of Failures Failure Rate Number/(100 mi)/(year)
Cast iron 33,611.0 8,204 24.4
Ductile iron 33,238.7 1,620 4.9
Polyvinyl chloride 26,840.3 689 2.6
Concrete pressure pipe 2,355.3 128 5.4
Steel 4,300.1 581 13.5
Asbestoscement 13,502.8 954 7.1
Other 3,755.3 787 21.0
Total 117,603.4 12,963 11.0
FIGURE 3
Total miles of pipe in each size group
35,000 30,000 25,000
Total Length of Pipemi
20,000 15,000 10,000 5,000
0
0500 5001,500 1,5003,000 Utility Size Group
(in miles of pipe)
3,0005,000
Total length of pipe classified according to
material type from the basic survey
FIGURE 4
40,000 35,000 30,000 25,000 20,000
Other includes HDPE, galvanized steel, and
copper
Pipemi
15,000 10,000 5,000 0
CI
DI
PVC CPP Steel AC Other
ACasbestoscement, CIcast iron, CPPconcrete
pressure pipe, DIductile iron,
HDPEhigh-density polyethylene, PVCpolyvinyl
chloride
74 OCTOBER 2012 JOURNAL AWWA 10410 FOLKMAN
ET AL
6
different failure rates for the same pipe
material. This finding should not be surprising.
Several significant variables affect pipe
performance, including age, soil types
(corrosive or noncorrosive), corrosion preven-
tion techniques, installation prac- tices, and
climate. Thus a utility may have a significantly
different failure rate from those reported here.
To compute an average failure rate for a given
pipe material, a large num- ber of respondents
are needed. Failure rates for each pipe material.
The basic survey measured pipe fail- ures over
a recent 12-month period, broken down by
material type. Table 1 lists the total length of
pipe by material type, the number of fail- ures
over a recent 12-month period, and the failure
rate for each pipe material. Figure 12 shows the
failure rates as a function of material type,
and Figure 13 classifies the failure rates by
material type and by US and Canadian
respondents. When the failure rates per 100 mi
of pipe per year were compared for cast-iron,
ductile-iron, PVC, concrete, steel,
and AC pipes, PVC was shown to have the lowest
overall failure rate. Plans for replacing water
mains. The detailed survey asked whether
respondents had a plan for regular replacement
of water mains that are nearing their end of
useful life. More than 77 reported they do have
a replacement plan in place. The survey also
asked what percentage of water mains are beyond
their useful life but
the maximum life out of a water main. The survey
asked whether the respondents utilities used
contractor experience as a weighting factor dur-
ing the selection process. Sixty-six percent of
respondents do consider contractor experience.
Many of those respondents who do not con- sider
contractor experience reported that state or
local laws prevented them from doing so.
it is imperative that utilities make wise choices
when repairing and replacing pipe, and
benchmarking can provide guidance in making those
decisions.
have yet to be repaired/replaced because of a
lack of funds. Respon- dents reported that from
zero to 75 of their pipe was beyond its useful
life. The average of all respondents showed that
8.4 of the pipe is beyond its useful
life. Contractor experience. Proper installation
is important to getting
Allowed pipe materials. Results from the survey
indicated that 87.2 of utilities would allow
installation of ductile iron, 59.6 of PVC,
38.3 of concrete pressure, and 36.2 of steel
pipe. Typical comments regarding pipe exclusion
included corrosion issues for duc- tile iron
and steel and strength,
FIGURE 5
Percentage of total length of pipe classified by
material type from the surveys
Basic Detailed
35
30
29
28
28
27
25
25
23
Total Length
20 15
12 11
10
5
4
3
3
3
2
2
0
CI
DI
PVC
CPP
Steel
AC
Other
ACasbestoscement, CIcast iron, CPPconcrete
pressure pipe, DIductile iron, PVCpolyvinyl
chloride
FOLKMAN ET AL 10410 JOURNAL AWWA
OCTOBER 2012 75
7
FIGURE 6 Regional percentage of length of pipe
classified by material type from the basic survey
Other AC
Steel CPP
PVC CI DI
9
8
7
6
Region
5
4
3
2
1
0
10
20
30
40
50
60
Installed Length ACasbestoscement, CIcast
iron, CPPconcrete pressure pipe, DIductile
iron, PVCpolyvinyl chloride
76 OCTOBER 2012 JOURNAL AWWA 10410 FOLKMAN
ET AL
8
tapping difficulties, and bedding concerns for
PVC. Comments regarding CPP included difficult
to install, tap, and repair and has corrosion
issues. Leak-detection methods. The detailed
survey asked respondents whether regular
leak-detection methods were used at their
utility, and 57 indicated that they were. The
methods of leak detection used included acoustic
leak detectors, visual inspection of lines,
digital correlation sensors, and eddy cur- rent
detectors. Corrosive soils and corrosion pre-
vention treatments. The detailed sur- vey asked
respondents whether there are one or more
regions in their service area with soils that
are corrosive. A total of 75 of the
respondents reported that they have at least one
area with corrosive soils. Thus, corrosion is a
signifi- cant problem for most of the re-
spondents. The survey also asked what kind of
corrosion treatments they are currently using.
Typical corrosion prevention treatments for DI
pipe included polywrap and the installation of
magnesium anodes. Covered bedding improvements,
type 50 concrete, coatings, and the use of
anodes were common treat- ments for CPP. Steel
pipe corrosion treatments listed impressed
current, anodes, and protective coatings. Effect
of ambient temperature on fail- ures. The
detailed survey asked whether the utility
observed an increase in water main failures with
extreme ambient temperatures, either warm or
cold. The results indicated that 72 of the
respondents did note an increase in pipe
failures with extreme cold ambient temperatures
and only 13 reported a correlation with warm
temperatures. Clearly this result would be
dependent on the cli- mate at each utility.
FIGURE 7
Percent of pipe length classified according to
age from the detailed survey
50
43.3
40
Total Length
30
22.2
18.4
20
14.9
10
1.3
0
010
1020
2050
gt 50
Unknown
Pipe Ageyears
FIGURE 8
Percentage of pipe length classified according to
pipe diameter from the detailed survey
70 60
65.9
50
Total Length
40
30 20
18.4
10.1
10 0
3.4
2.2
1014
1624
3036
S 36
S 8
Pipe Diameterin.
Percent of respondents selecting a most common
failure mode
FIGURE 9
60
50
50
Respondents
40
28.3
30
20
13.0
10
4.3
2.2
2.2
0
CONCLUSION To capture statistically signifi-
cant water main break data that can provide an
accurate portrayal of current pipe behavior and
water
Other
Fatigue
Leak
Longitudinal Crack
Corrosion
Circumferential Crack
FOLKMAN ET AL 10410 JOURNAL AWWA
OCTOBER 2012 77
9
utility practices requires a large number of
participants. The total miles of pipe covered by
this sur- vey is almost 10 of that in use in
the United States. From these data many
observations can be made at a national level and
applied to
  • individual utilities as possible internal
    benchmarks.
  • There are approximately 264 people who are
    served per mile of water main pipe, which is an
    average number representing both rural and
    urban populations.
  • The primary water main pipe materials in use
    today are cast iron (28 of the installed base),
    ductile iron (28), and PVC (23). The survey
    results indicate that the type of pipe material
    installed varies sig- nificantly across the
    regions approx- imately 90 of the pipe in the
    northeastern United States is either ductile or
    cast iron, whereas PVC is the dominant pipe in
    Canada.
  • Water main pipe characteristics uncovered by the
    survey indicate that more than 22 of currently
    installed pipe is more than 50 years old and
    that about 66 of water mains are 8 in. or less
    in diameter. The average age of a failing water
    main was only 47 years, with 8.4 of pipes
    classified as being beyond their useful life.
    These results are in sharp contrast to
    respondents beliefs that new pipe should last
    79 years on average.
  • The average delivery pressure is 77 psi and 83
    of utilities keep water pressure fluctuations at
    less than 20 psi.
  • The survey also found various limitations placed
    by utilities on pipe materials. The percentage
    of utilities allowing installation of specific
    pipe materials is as follows ductile-iron
    pipe87, PVC pipe60, con- crete pressure
    pipe38, and steel pipe36.
  • Utilities exhibit a large variation in water
    main failure rates.
  • Approximately 75 of utilities have at least one
    region in their ser- vice area with corrosive
    soils.
  • This survey found that on the basis of the
    number of failures per 100 mi of pipe per year,
    PVC pipe currently has the lowest overall
    failure rate.
  • Information from this survey is intended to
    assist utilities in seeing how they compare with
    national norms. The amount of pipe ap-
    proaching the end of its life is grow- ing. It
    is imperative that utilities make wise choices
    when repairing and replacing pipe, and
    benchmark- ing can provide guidance in making
    those decisions.

FIGURE 10 Percent of respondents selecting a most
common failure material
60
55.3
50
40
Respondents
30
20
17.0
10
6.4
6.4
4.3
4.3
2.1
0
CI
DI
PVC
CPP
Steel
AC
Other
ACasbestoscement, CIcast iron, CPPconcrete
pressure pipe, DIductile iron, PVCpolyvinyl
chloride
Total failure rates at each utility relative to
miles of pipe for all pipe materials
FIGURE 11
70
60
(Number of Failures)/(100 mi)/year
50
40
30
Average
20
10
0
0
1,000
2,000
3,000
4,000
5,000
Pipemi
78 OCTOBER 2012 JOURNAL AWWA 10410 FOLKMAN
ET AL
10
ACKNOWLEDGMENT This work was completed with
support from Uni-Bell PVC Pipe Association and
the Water Finance Research Foundation.
FIGURE 12 Failure rates of each pipe material per
100 mi over a one-year period
30
ABOUT THE AUTHORS
24.4
25
Steven Folkman is an associate professor at
Utah State University, 4130 Old Main Hill,
Logan, UT 84332-4130 steven.folkman_at_
21.0
Failures/(100 mi)/year
20
15
13.5
10
7.1
5.4
4.9
5
2.6
usu.edu. A member of AWWA, Folkman has oversight
of Utah States Buried Structures Laboratory,
is co-author of Buried Pipe Design, and has been
involved with analysis and testing of buried
structures for more than 20 years. His work has
been published previously in Journal of Civil
Engineering and Architecture and Transportation
Research Record. He received his BS, MS, and PhD
degrees from Utah State University. John Rice
is an assistant professor and Ammon Sorensen and
Nathan Braithwaite are research assistants, all
at Utah State University.
0
CI DI PVC CPP Steel AC Other ACasbestoscement,
CIcast iron, CPPconcrete pressure pipe,
DIductile iron, PVCpolyvinyl chloride
FIGURE 13 Failure rates reported in this survey
by US and Canadian respondents
US Canada
REFERENCES Royer, M.D., 2008. Condition
Assessment of Drinking Water Transmission and
Distri- bution Systems. Presented at EPA Sci-
ence Forum 2008, Washington, D.C., May 2022,
2008. www.epa.gov/awi/ pdf/600f09030.pdf
(accessed Aug. 31, 2012). US Census, 2011.
www.census.gov/ (accessed Oct. 5, 2011). USEPA
(US Environmental Protection Agency), 2007.
Distribution System Inventory, Integrity and
Water Quality. www.epa.gov/ogwdw/disinfection/tcr
/ pdfs/issuepaper_tcr_ds-inventory.pdf
(accessed Aug. 31, 2012).
40
35.0
35
30
Failures/(100 mi)/year
23.9
25
21.3
20
15.2
15
13.8
13.4
10
7.0 7.5
6.2
4.3
3.9
5
2.9
0.9
0.7
0
CI
DI
PVC
CPP
Steel
AC
Other
http//dx.doi.org/10.5942/jawwa.2012.104.0135
ACasbestoscement, CIcast iron, CPPconcrete
pressure pipe, DIductile iron, PVCpolyvinyl
chloride
Journal AWWA welcomes comments and feedback at
journal_at_awwa.org.
FOLKMAN ET AL 10410 JOURNAL AWWA
OCTOBER 2012 79
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