oERA
United States
Environmental Protection
Agency
Office of Water (4601M)
Office of Ground Water and Drinking Water
Distribution System Issue Paper
Deteriorating Buried Infrastructure
Management Challenges and Strategies
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PREPARED FOR:
U.S. Environmental Protection Agency
Office of Ground Water and Drinking Water
Standards and Risk Management Division
1200 Pennsylvania Ave., NW
Washington DC 20004
Prepared by:
American Water Works Service Co., Inc.
Engineering Department
Background and Disclaimer
The USEPA is revising the Total Coliform Rule (TCR) and is considering new possible
distribution system requirements as part of these revisions. As part of this process, the
USEPA is publishing a series of issue papers to present available information on topics
relevant to possible TCR revisions. This paper was developed as part of that effort.
The objectives of the issue papers are to review the available data, information and
research regarding the potential public health risks associated with the distribution
system issues, and where relevant identify areas in which additional research may be
warranted. The issue papers will serve as background material for EPA, expert and
stakeholder discussions. The papers only present available information and do not
represent Agency policy. Some of the papers were prepared by parties outside of EPA;
EPA does not endorse those papers, but is providing them for information and review.
Additional Information
The paper is available at the TCR web site at:
http://www.epa.gov/safewater/disinfection/tcr/requlation revisions.html
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DETERIORATING BURIED INFRASTRUCTURE
MANAGEMENT CHALLENGES AND STRATEGIES
Prepared by
American Water Works Service Co., Inc.
Engineering Department
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DETERIORATING BURIED INFRASTRUCTURE
MANAGEMENT CHALLENGES AND STRATEGIES
Table of Contents
I. Introduction 1
II. Buried Infrastructure Challenges Facing the Water Industry 2
A. Current condition/status of buried infrastructure 2
B. Industry assessment and estimate of costs 5
C. Verification of industry cost estimates 5
D. Justifying capital investments 6
E. Regulations affecting buried infrastructure 9
III. Buried Infrastructure Technical Considerations 11
A. Recommendations for extending pipe life 11
B. Rehabilitation Technologies 14
C. Preventative Technologies 21
D. Analysis of distribution pipe materials for future use 22
IV. Value Added Management Strategies for Buried Infrastructure 24
A. Broad based infrastructure assessment methods 24
B. Performance based buried infrastructure management approach 24
C. Data Management 28
V. Implementation 28
VI. Conclusions 29
VII. References 31
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DETERIORATING BURIED INFRASTRUCTURE
MANAGEMENT CHALLENGES AND STRATEGIES
I. Introduction
The findings of several prominent studies forecasting capital investment needs for water
systems has brought the subject of buried infrastructure asset management to the forefront of
priority issues facing the water industry. The capital investment focus of these studies and
numerous other published articles has overshadowed any discussion or concern of the potential
health risks associated with deteriorating distribution systems. The United States Environmental
Protection Agency (USEPA), in an effort to assess the need for regulatory action, has directed
preparation of several White Papers (including this paper) to address health risks related to
specific water distribution system topics. The characteristics of deteriorating water distribution
systems include the increased frequency of leaks, main breaks, taste, odor and red water
complaints, reduced hydraulic capacity due to internal pipe corrosion, and increased disinfectant
demands due to the presence of corrosion products, biofilms, and regrowth. Each of these
conditions presents the potential for water quality degradation, and the specific causes, health
risks and mitigation strategies are appropriately being addressed by individual White Papers
dedicated to these topics. This paper will not duplicate that work but rather will compliment
these papers by providing a broad assessment of current buried infrastructure management
challenges and strategies for addressing them.
These broader challenges associated with buried infrastructure include establishing a
means for monitoring and measuring all impacts associated with deteriorating water systems and
their relative importance. These impacts include health risks as well as customer service,
community disruption, customer confidence, public perception, fire protection, and other less
tangible variables. State and Federal subsidies will likely be unavailable or insufficient to fully
address this issue, and the needed capital funds will be limited by increasing demands to keep
water rates affordable. Investment in buried infrastructure will also be in direct competition with
other more visible and regulatory driven infrastructure needs. Historically, buried infrastructure
investment, absent regulatory compliance directives, or gross system failures, have been
subordinate to regulatory driven investment or capital needs associated with more highly visible
projects. The competition for capital funds is made more difficult when a comparison of "direct"
costs of repair versus rehabilitation or replacement almost always favors continuing to repair a
deteriorated water main. Therefore, a utility must measure and present credible evidence of the
indirect costs and impacts associated with poorly performing systems including service
interruptions, community disturbance, and health risks in order to support the need for capital
investment.
The rate of deterioration of a water system is not a function of material age but rather the
cumulative effect of the external forces acting on it. During a recent water system valuation,
70+-year-old unlined cast iron main was found to be in excellent condition with negligible
internal or external corrosion. Based on the field observations, there is no reason to believe that
these mains will not provide another 70+ years of satisfactory service. Conversely, in another
system, cast iron mains less than 50 years old are experiencing excessive and rapidly increasing
break rates and severe corrosion activity. Planned replacement of these mains is needed in the
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near future. Therefore, broad based decision factors regarding infrastructure replacement,
whether based on age, pipe size, pipe material, linings, etc. will not result in an effective use of
limited capital resources. Better information and decision making is needed. Lastly, with
numerous pipeline rehabilitation technologies and new pipeline materials emerging, the question
of how best to remedy a poorly performing water main must be answered. This question can
only be answered through actual knowledge of the conditions and service characteristics of the
existing main, comparative repair, replacement, and rehabilitation costs, and an understanding of
what is being gained via the various rehabilitation techniques available. This paper will address
these issues and provide a basis for sound management of buried infrastructure assets moving
foreword.
II. Buried Infrastructure Challenges Facing the Water Industry
The buried infrastructure challenges facing the water industry are an interrelated mix of
technology, financial, customer and community service, and regulatory issues. This section will
summarize the condition of buried infrastructure in this country, the positions of various industry
groups and organizations including their estimates of needed capital, the concerns with justifying
the capital expenditures, and potential new regulations that may affect the future management of
buried infrastructure.
A. Current Condition/Status of Buried Infrastructure
The majority of distribution piping installed in the United States, beginning in the late
1800's up until the late 1960's, was manufactured from cast iron. The first cast iron pipe
manufacturing process consisted of pouring molten iron into a sand mold, which stood on end in
a pit in the ground, similar to how concrete is poured into a form. Pipe manufactured by this
method is referred to today as "pit" cast iron pipe. Due to the potential inconsistencies that could
occur in the pipe wall thickness, the pipe was designed with a wall thickness that was much
greater than that required for the internal working pressure or external loading to which the pipe
would be subjected. When installing the pipe in the field, the joints were sealed with rope and
lead that was heated, poured in a molten state, and allowed to cool. Although pit cast iron pipe
has no interior or exterior corrosion protection, it has performed well within the industry as a
result of the added wall thickness.
In 1920, the process of centrifugally casting pipe in a sand mold was introduced. Pipe
that was manufactured by this process is referred to as "spun" or "centrifugally" cast iron pipe.
The centrifugal forces that are induced on the molten iron alter the molecular composition of the
metal and increase its tensile strength. The higher strength coupled with the lack of
inconsistencies in the wall thickness resulting from the centrifugal action allowed the pipe to
have a much thinner wall than pit cast iron pipe. Interior lining of the pipe with cement to
prevent corrosion was also introduced in the early 1920's; however, it did not gain wide
acceptance until the late 1930's. The process of centrifugally casting pipe was improved in the
early 1930's with the use of a water-cooled metal mold that allows the pipe to be immediately
withdrawn from the centrifuge. This process, which is known as the "deLavaud" process, is still
in use today for the manufacturing of ductile iron pipe. Although the centrifugal casting process
improved pipe strength and minimized casting imperfections, the reduction in wall thickness
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coupled with the lack of exterior corrosion protection has resulted in a failure rate in the industry
that is higher than the older pit cast iron pipe.
In the late 1920's a plasticized sulfur cement compound was developed as an alternate to
lead for sealing the pipe joints in the field. This compound is referred to as "leadite". Leadite
was commercially produced up until the early 1970's, and was used extensively from 1941 to
1945 when lead was scarce as a result of raw material needs associated with World War II.
Ultimately, leadite was found to be an inferior product to lead for two reasons. First, leadite has
a different coefficient of thermal expansion than cast iron and results in additional internal
stresses that can ultimately lead to longitudinal splits in the pipe bell. Secondly, the sulfur in the
leadite can facilitate pitting corrosion resulting in circumferential breaks on the spigot end of the
pipe near the leadite joint. The failure rate in the industry for leadite joint pipe is significantly
higher than for lead joint pipe even though the pipe may not be as old.
Beginning in the mid-1950's, improvements in iron pipe manufacturing and technology
began to emerge. The first improvement was the advent of the rubber gasketed joint that
alleviated shortcomings associated with leadite and rigid joints. The next major improvement
was the introduction of ductile iron pipe in the late 1960's. Ductile iron differs from cast iron in
that its graphite form is spheroidal, or nodular, instead of the flake form found in cast iron. This
change in graphite form is accomplished by adding an inoculant, usually magnesium, to molten
iron of appropriate composition during manufacture. Not only is ductile iron pipe stronger than
cast iron pipe, it is also more resistant to corrosion. Cast iron pipes, whether pit cast or spun
cast, are susceptible to "graphitic" corrosion where which an electrochemical reaction occurs
between the cathodic graphite component (flakes) and the anodic iron matrix causing metal loss.
Due to its spheroidal graphite form, ductile iron is not subject to graphitic corrosion and also has
approximately twice the strength of cast iron as determined by its mechanical properties. Its
impact strength and elongation are also many times greater than cast iron. Exhibit No. 1 below
shows the molecular differences in ductile iron and cast iron.
Exhibit No. 1
Differences in Graphite Form
between Ductile and Cast Iron
vj r
* w**
ป . J*
ซ ซ, " ป *
. 1'/ 1 / " f *
t \
ฆ
' ป ; ** , . '
* ป * _ 'ป ซ *
. A / , ฆ . ป*~
* ซ .\ " *ฆ
* 1 ป *
* m , m m
.* . , *
, * , i ' s
* *, J* **
DUCTILE IRON
/"*-V *' i j
* v ซ . < t *. > 7* . + ;
* r 7' V#. '
;i* - %
. ' .-:--
<* ,Vu" pv
33?
i - &
CAST IRON
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B. Industry Assessment and Estimate of Costs
In March of 2001, the American Society of Civil Engineers (ASCE) released their
"Report Card for America's Infrastructure". Overall, this report card indicated that the nation's
infrastructure is in poor condition. Drinking Water, Wastewater, and Dams, received very low
grades in relation to other categories of infrastructure. The only category receiving lower grades
was public school infrastructure.
A number of professional organizations have addressed infrastructure concerns related to
drinking water, and some have developed cost estimates. In addition to ASCE, these
organizations include the USEPA, the American Water Works Association (AWW A), the Water
Infrastructure Network (WIN), and the Help to Optimize Water (H20) Coalition. WIN is a
broad-based coalition of local elected officials, drinking water and waste water service providers,
state environmental and health administrators, and engineers and environmentalists who support
the concept of federal financial assistance. The H2O coalition is comprised of the National
Association of Water Companies (NAWC), the Water and Wastewater Equipment
Manufacturers Association, and the National Council for Public-Private Partnerships. This
coalition recognizes that short term federal financial assistance may be needed, but wants water
utilities to be self-sustaining, not subsidized enterprises, over the long term. A summary of the
professional organization cost estimates related to drinking water infrastructure are provided in
Exhibit No. 3 below. Except where noted, these estimates are for all drinking water
infrastructure, including treatment plants, and encompass infrastructure needs due to regulation
and deterioration but not new infrastructure associated with growth.
Exhibit No. 3
Cost Estimates for Drinking Water Infrastructure
Profession;!!
( osl
Oi'^iini/iilioii
I'.Miniiili-
Period
(0111 UK-Ills
ASCE
$11 B
per year
USEPA
$151 B
next 20 years
$83 B of this amount for transmission and distribution piping
AWWA
$250 B
next 30 years
WIN
$460 B
next 20 years
includes both water and wastewater
H20 Coalition
none
none
believes more analysis is needed
C. Verification of Industry Cost Estimates
In order to conduct a rough, order of magnitude, check of the industry cost estimates, a
methodology was used whereby an annual range of costs for buried infrastructure was calculated
based on the industry estimates, then verified by comparing it with known information for a large
water utility.
First, the USEPA was the only organization that provided a breakdown between
transmission/distribution and treatment plant cost estimates. Their transmission and distribution
cost estimate was 55% of their total cost estimate ($83B of $151B). Thus, it was assumed that
approximately 55% of the cost estimates provided by each of the other organizations was
allocated for transmission and distribution. Applying this to each of the industry estimates and
annualizing them results in a range of costs between $4.2B to $6.3B per year.
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Second, the population served by community water systems was compared to the
population served by the selected utility. As of April, 2000, approximately 264 M people were
served by community water systems, and approximately 10M people were served by the selected
utility (3.8%). Thus, taking 3.8% of the annualized range of costs calculated above results in an
annual range of costs for transmission and distribution piping of $160M to $240M per year, with
an average of $200M per year for the utility, based on industry estimates.
Lastly, the selected utility has approximately 40,000 miles of main. Assuming an
average pipe installation cost of $75 per foot, and a range of pipe life between 75 to 100 years,
the estimated range of expenditures is $158M to $211M per year. This compares favorably with
the industry cost estimate range of $160M to $240M per year. However, it is important to note
that this range of costs would not reflect the degree to which a utility may be behind in terms of
pipe replacement. Thus, based on this rough analysis, it appears that the industry cost estimates
for buried infrastructure are reasonable.
D. Justifying Capital Investments
One of the key components of infrastructure assessment is the estimate of the useful life
of the asset. When is it time to replace the pipe? The following case history illustrates this
challenge in more detail. A large mid-western water utility has done considerable work in their
efforts to manage main breaks over the last few years. The system serves over 300,000
customers with a distribution system of over 4,000 miles of mains. They currently experience
about 2,000 breaks per year. This equates to about 5V2 breaks per day. In December 1999 during
a particularly cold period, it experienced 1,000 main breaks. Exhibit No. 4 shows that main
breaks in the system have been increasing over the years, especially the rigid joint, spun cast iron
pipe. Using this data, an engineering economic analysis was performed by analyzing data from a
computerized leak database containing over 30,000 records since 1983. The result was a main
break forecasting model for individual mains in the system and an engineering economic model
to estimate the total life cycle costs of each pipe with three or more breaks.
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Exhibit No. 4
Main Breaks Since 1965
2,500
2,000
total
spun, rigid
aa
E
S i.ooo
as
spun, flex
pit cast
idaBU
1975
ductile ปooo
1980
1965
1990
1995
Date
Exhibit No. 5 presents an example of a pipeline's total life cycle costs derived from the
model. The line sloping downward indicates the present worth of the replacement cost. The line
sloping upward indicates the cumulative costs to repair the pipe. The top line indicates the
addition of the other two curves, which represents the total life cycle cost of the pipeline. In
other words, it shows how much money must be set aside today to finance the continual repair
and/or eventual replacement of this pipeline. From the graph, it can be concluded that the
optimal time to replace the pipe is when the total life cycle cost reaches a minimum.
By applying this approach the utility could support that 146 miles of pipe should be
replaced today, and furthermore, could identify the individual pipes that should be replaced.
Although more analysis is required, the initiative is moving forward to phase in an accelerated
main replacement program.
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Exhibit No. 5
Economic Break Even Analysis
$300,000
Pipe length = 2,795 feet
Indirect costs not considered
Repair cost = $3,120
Replacement cost = $92.77 per foot
$250,000
Total Cost
$200,000
minimum Total Cost
Replacement Cost
$150,000
$100,000
$50,000
Repair Cost
Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09 Jan-10 Jan-11 Jan-12
Date
This is an extraordinary case due to the unusually high number of main breaks. Most
water utilities are not experiencing main breaks at such a rate and cannot economically justify
replacement over repair. It also is important to note that the economic model is based on
standard engineering economics, and does not incorporate financial factors such as taxes on
capital investment and depreciation. If these additional factors were considered, the analysis
would slant further in favor of repairing instead of replacing mains.
Consider the following example where actual direct costs for replacement and repair are
compared. Average replacement costs are approximately $100/foot for 6-inch main. Therefore,
for a 1,000-foot main, total replacement costs would be approximately $100,000. If the utility
expects to recover that investment, the annualized revenue requirement or cost would be $10,000
to $15,000, depending on financing cost or economic regulation (investor-owned utilities).
Repair costs on the main are approximately $3,000 per break. Consequently, in order to justify
replacing that pipe purely from a cost standpoint, the main must experience breaks at a rate of
approximately 3 to 5 per year. A rate of 4 breaks per year is a break every 3 months for a length
of pipe slightly longer than a city block. Such a high break rate is very unlikely and certainly
would not be tolerated by customers subjected to such frequent service and traffic disruptions.
Therefore, other factors such as the stakeholder and liability costs associated with main breaks
must also be considered.
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Liabilities associated with main breaks can be quite significant. A single break can incur
liability costs that total more than the replacement cost of the main. Service disruptions can
result in lost revenue and other risks to customers that depend on reliable water service (e.g.
hospitals, restaurants, commercial properties, laundry mats, etc.). Traffic disruptions equate to
lost time from work for stakeholders. Consideration should also be given to the monetary value
of water lost during the break, including pumping, chemical, and waste disposal costs. These
costs can be significant for large main breaks, especially if they empty tanks. One study
estimated that these indirect costs could equal 20% to 40% of the repair costs.
Other important issues should be considered, including effects on water quality and the
reputation of the utility. Main breaks can cause loss of system pressure, which poses the threat
of contamination. Neglected distribution piping often breeds poor water quality due to corroded
pipelines, resulting in numerous customer complaints. These problems result in poor customer
service that can damage the reputation and credibility of the utility.
It is difficult to justify replacement of mains on direct costs alone. Although this can be
done in some circumstances where break rates are excessive and/or replacement costs are very
low, for most pipelines it will be less costly to continually repair the main than to replace it if
direct costs alone are considered. However, direct costs do not present the full impact to the
utility. Instead, we must consider the indirect costs and stakeholder issues discussed above in
order to maintain system integrity and reliability so that acceptable customer service can be
assured.
E. Regulations Affecting Buried Infrastructure
1. Potential Health Effects
In addition to this paper, other White Papers being prepared in response to the USEPA
assessment of health risks and the need for distribution system regulation include:
a. Contamination of New or Repaired Mains
b. Permeation and Leaching
c. Intrusion into Pipes
d. Microbial Regrowth/Biofilms
e. Covered Storage Vessels
f. Decay of Water Quality in Pipe with Time
g. Cross Connections
h. Nitrification
Papers a through d above cover the specific causes, health risks, and mitigation strategies
associated with the characteristic signs of deteriorated water distribution systems. These papers
discuss the deleterious effects of internal corrosion on water quality and also address external
sources of contamination and the potential pathways into the distribution system during repair
activities or during negative pressure events associated with water hammer occurrences. In
general, internal corrosion by-products, including the formation of tubercles (oxidized metals at
the anode deposited back on the pipe wall), cause taste, odor and color problems and impart a
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disinfectant demand on distributed water. Additionally, corrosion by-products can shield
microorganisms from disinfectants and serve as a nutrient and physical substrate for their
growth. Leaking mains and repair activities introduce pathways for external contamination
including pathogen and harmful chemical intrusion. Sources of these contaminants include
adjacent soils harboring microbial activity, leaking sanitary sewers, storm water runoff,
chemically contaminated soils, and exposure to animal wastes. The findings of these papers
needs to be incorporated in the overall management planning for aging distribution systems and
used to clearly support the need for capital investment.
2. New A ccounting Regulation
The Governmental Accounting Standards Board (GASB) was formed in 1984 to develop
and improve financial reporting rules for the 85,000 state and local governments in the United
States. It operates under the auspices of the not-for-profit Financial Accounting Foundation,
which oversees, funds, and appoints the members of the GASB, as well as the Financial
Accounting Standards Board (FASB). GASB is not part of the government, federal or otherwise.
Its rules are required in most states for financial reporting at the local and state level. GASB
rules also are required to be followed when a state or local government's audit reports that it
follows Generally Accepted Accounting Principles (GAAP). Bond covenants associated with
government debt often require them to follow GAAP.
GASB Statement No. 34 (GASB 34) was modified in June 1999. It requires, for the first
time, that governments begin including infrastructure assets on their balance sheets. After
estimating the initial cost of each infrastructure asset and including that cost in the balance sheet,
governments will be required to either depreciate those assets, or manage them using an asset
management system. GASB 34 prefers that municipalities implement an asset management
system referred to as the "modified approach" because it better models the way infrastructure
should be treated. There are specific requirements for the implementation of the asset
management system, and reporting that must be produced.
Whichever method is used, a fundamental requirement is a good inventory of assets. The
inventory must include the actual or estimated historical cost of construction. The most
straightforward method for valuing assets is depreciation, but this method ignores the extended
life of the asset provided by continued maintenance. The modified approach incorporates the
benefits, or value, of such maintenance activities. GASB 34 provides the following minimum
guidelines as to what the modified approach should include:
a. The assessed physical condition of infrastructure assets (governments must
perform such assessments at least every three years, and disclose the results of at
least the three most recent condition assessments).
b. Descriptions of the criteria the government uses to measure and report asset
condition.
c. The condition level at which the government intends to maintain the assets.
d. A comparison of the annual dollar amount estimated to be required to maintain
and preserve the assets at the condition level established by the government with
the actual expenses, for at least the last five years.
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Although not prescribed in detail, GASB 34 requires that governmental entities use
"consistent" and "reasonable" methods for valuing assets. The GASB 34 rule should have a
positive effect on addressing aging infrastructure by continuously measuring the condition of a
buried water system and quantifying investment needs and past deficiencies.
Municipalities must be in compliance with GASB 34 by July 2001, 2002, or 2003
depending on the government's annual revenue base in 1999. Only new infrastructure (added or
reconstructed) need be included beginning on those dates. An additional four years are granted
before pre-existing infrastructure need be reported. If revenue base was less than $10 million in
FY 1999, a municipality is encouraged, but not required, to report pre-existing infrastructure.
III. Buried Infrastructure Technical Considerations
In order to address the concerns raised by the water industry, it is first necessary to
further understand the technical aspects of buried infrastructure in order to develop appropriate
management strategies. This section will address the failure mechanisms of pipe, potential
rehabilitative and preventative technologies, and recommendations for pipe materials for future
use.
A. Recommendations for Extending Pipe Life
In order to minimize main failures and maximize the life of the assets, it is necessary to
understand the failure mechanisms of pipe. These failure mechanisms, which are a result of
either Operational/Physical or Chemical means, are identified in Exhibit No. 6.
Exhibit No. 6
Pipe Failure Mechanisms
OlHTiilioiiiil/Plnsiciil
Applies In
Options
Chcmiciil
Applies Ki
Options
Manufacturing defects
M,P,C
No
Internal corrosion
M,C
Yes
Improper design/installation
M,P,C
No
External corrosion - soil
M,C
Yes
Geologic instability
M.P.C
No
External corrosion - other
M,C
Yes
Higher operating pressures
M,P,C
Yes
Leadite corrosion
M
Yes
Hydraulic transients
M,P,C
Yes
Leadite expansion
M
Yes
Change in water temperature
M
Yes
Material incompatibilities
M
Yes
Excessive external loads
M,P,C
No
Gasket deterioration
M,P,C
Yes
Damage from digging
M.P.C
No
Material fatigue
P
No
M = Metallic (ductile iron and/or cast iron)
P = Plastic (PVC or HDPE)
C = Concrete (RCP or PCCP)
This exhibit indicates the type of pipe to which the failure mechanism is applicable
(metallic, plastic, or concrete) and whether there are any options to reduce or eliminate the
failure mechanism for pipes that are already installed in the ground. If so, these are addressed in
a subsequent exhibit. Nearly all of these failure mechanisms can be addressed or controlled for
new installations as a result of newer pipe materials, current manufacturing technology, and
improved utility operational practices.
A few of these failure mechanisms warrant additional discussion as follows:
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1. Hydraulic Transients: Hydraulic transients (water hammer) occur as a result of a
sudden change in flow velocity. Some ways that this can occur are due to a
sudden starting or stopping of a pump, closing or opening a hydrant too quickly,
or sudden starting and stopping of water usage by large customers. As a rule of
thumb, for every 1 ft/sec instantaneous change in flow velocity, the pressure can
change by 100 ft (43.3. psi). It is important to understand the variables which
effect the magnitude of the pressure change as defined by the Joukowsky
equation:
H = 4660 * (Vi-Vf) where:
(1+ Ml* ID)0'5*ฎ
Mp th
H = pressure increase (ft)
Mw = bulk modulus of water (psi)
Mp = bulk modulus of pipe materials (psi)
ID = inside diameter of the pipe (in)
th = wall thickness of the pipe (in)
g = acceleration due to gravity (ft/sec )
Vi = initial water velocity (ft/sec)
Vf = final water velocity (ft/sec)
It can be seen in this equation that the materials of construction (Mp) and the
geometrical strength of the pipe (ID/th) also affect the magnitude of the pressure
change. With the same change in velocity, a stronger, more rigid pipe will
experience a higher pressure change. The second item to note is that water
hammer is independent of volume. It is also important to be aware of operational
situations that could promote hydraulic transient events as listed below:
Pipeline velocities > 5 ft/sec
Non-networked pipelines (transmission mains)
Dead end pipelines and closed (no tanks) systems
Undulating topography
Combination vacuum relief/air release valves of the same size
Pumps with swing check valves or no control valves
Frequent power failures at pump stations
2. Change in Temperature: Utilities with cast iron pipe typically experience an
increase in main failures with freezing temperatures. Although plastic pipes also
are affected by a change in temperature due to their high coefficient of thermal
expansion, it is less of an issue due to the flexibility of the pipe, and the
phenomena of concern discussed here applies only to iron pipes. One theory of
why iron pipes fail in freezing temperatures is that the ground movement imposes
a stress on the pipe. Although this may be true, the primary reason for the failures
relates to the differences in thermal expansion between water and iron. As water
and the pipe cool, they are both contracting until the temperature reaches 39 deg
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F. At this point, the pipe continues to contract, but the water begins to expand.
This can result in a stress equivalent to that of increasing the hydrostatic pressure
in the pipe by approximately 200 psi.
3. Corrosion (internal): Internal corrosion of water distribution systems leads to
two major problems for water utilities. The first is the failure of distribution
system pipes which can result in water leakage, loss of pressure, and potential
contamination during main installation and repair. The second problem is an
unwanted change in water quality as the water is being transported through the
distribution system (Snoeyink et al, 1996). Corrosion can occur without metals
leaching, i.e., oxidized metals released at the anode can be deposited back on the
pipe wall in the form of tubercles (Snoeyink et al, 1996).
During iron corrosion, the metal dissolves and the electrons are accepted in
cathodic reactions such as those involving the reaction of protons and oxygen.
These reactions are shown in Equations a through c (Snoeyink et al, 1996).
a. Me <->ฆ Mez+ + z e"
b. 2H+ + 2e" <-> H2
c. 02 + 2H20 + 4e" <-> 40H"
According to Benjamin, Sontheimer, and Leroy (1996), the corrosion of iron
piping in distribution systems can be either uniform or localized. Localized
corrosion can be caused by local nonuniformities in the pipe or the water quality
adjacent to it, and often leads to tuberculation.
When potable water containing dissolved oxidants (such as oxygen or chlorine) is
in contact with metallic iron, there is a driving force for active corrosion under
any realistic water quality conditions (Benjamin et al, 1996). The authors also
state that the corrosion rate is probably limited by the rate at which oxygen is
provided to the surface, which in turn is limited by molecular diffusion through
the layers of stagnant water and scale adjacent to the metal.
Ferrous ions or compounds in scales can be oxidized directly or microbially
mediated, resulting in a variety of end products. These corrosion products can be
released into the water due to physical or water quality factors, and therefore the
iron release rate often bears no relation to the overall corrosion rate (Benjamin et
al, 1996). Corrosion and the release of corrosion products can lead to chemical,
physical, and microbial degradation of distribution system water quality.
The internal corrosion of cement-based materials can impact both water quality
and infrastructure integrity. Cement-based materials include reinforced or
prestressed concrete pipes, cement-mortar linings, and asbestos-cement pipe.
Two general components of cement-based materials include the aggregates and
the binder. The binder consists of calcium silicates and calcium aluminates in
various proportions depending on the type of the cement (Leroy, Schock, Wagner,
and Holtschulte, 1996).
-------
Several types of degradation of cement materials can occur in the presence of acid
waters or waters aggressive to calcium carbonate (Leroy, Schock, Wagner, and
Holtschulte, 1996). Degradation can result in weakening of the material as well
as leaching of calcium carbonate and metals into the water. Water quality impacts
associated with lime and metals leaching from cement-based materials are
discussed further under Metals and Chemical leaching. Health effects associated
with the release of asbestos fibers from asbestos-cement pipe are addressed in the
Phase II National Primary Drinking Water Regulations (USEPA, 1991).
Microorganisms have the ability to induce or promote corrosion as well as take
advantage of corrosion deposits as growth habitats (Snoeyink et al, 1996).
Corrosion by-products such as tubercles, iron oxides, and other precipitates can
shield microorganisms from disinfectants and can serve as a physical substrate for
growth. Organisms such as Bacillus, Escherichia coli, Psuedomonas, and
Citrobacter have the ability to reduce Fe(III) to Fe(II) and have been found in
tubercles, but the role these organisms play in the corrosion process has not been
delineated (Snoeyink et al, 1996). Microbial regrowth and associated health
effects are discussed in a separate White Paper.
Internal corrosion can result in leaking or failure of distribution system pipes.
Leaks and breaks can serve as pathways for contamination from harmful
organisms originating exterior to the pipe environment. Potential health impacts
associated with pathogen intrusion are discussed in a separate White Paper.
4. Corrosion (external): The two basic types of external corrosion which can occur
in a water system are galvanic and electrolytic. The galvanic corrosion process
occurs when electrons flow from one metal (anode) to a dissimilar metal
(cathode) via an electrolyte (soil) with a return current path (the pipe).
Electrolytic corrosion is similar to galvanic corrosion with the exception that the
return current path includes a direct current source (stray current) which drives the
reaction.
Some of the specific types of external corrosion in pipelines include:
a. Pitting Corrosion - Occurs when protective films covering a metal break
down.
b. Bacteriological Corrosion - The result of sulfate reducing bacteria giving
off sulfides which are excellent electrolytes.
c. Soil Corrosion - Mostly occurs in soils with high electrical conductivity.
d. Graphitic Corrosion - Corrosion can occur in any metallic pipe. However,
the potential for corrosion is higher in cast iron pipes than in ductile iron
pipes. The corrosion phenomenon that occurs in cast iron (pit cast or spun
-------
cast) is called graphitic corrosion. Graphitic corrosion of cast iron is a
form of selective leaching where the iron matrix corrodes, leaving behind
porous graphite mass. The process affects buried cast iron pipe in
relatively mild aqueous environments. The corrosion mechanism involves
an electrochemical reaction between the cathodic graphite component and
the anodic iron matrix. Graphitic corrosion generally is a slow process. It
can cause significant problems since no dimensional or physical changes
occur which are visible, yet the cast iron loses its strength and becomes
brittle.
5. Leadite Corrosion and Expansion: As previously discussed, leadite has a
different coefficient of thermal expansion than cast iron resulting in stress on the
pipe which can ultimately result in longitudinal splits in the pipe bell. Secondly,
the sulfur in the leadite allows for bacteriological corrosion that can lead to
circumferential breaks on the spigot end of the pipe near the leadite joint.
6. Material Fatigue: There is no measurable relationship between ductile iron's
applied tensile strength and time to failure. However, both PVC and HDPE pipe
experience a reduction in strength over time.
Exhibit No. 7 identifies the strategies for reducing or eliminating pipe failures for those
pipes that are already installed in the ground. The potential for implementing these strategies is
also indicated.
Exhibit No. 7
Operational Strategies for Reducing or Eliminating Pipe Failures
l-'iiiluiv Mi-chiiiiism
Slr;ik'U>
I'ok-nlhil
Higher operating pressures
Redistribution of pressure zones
Low
Hydraulic transients
Surge control and operator training
Medium/High
Change in water temperature
Blending with ground water sources, where possible
Low
Internal corrosion
Cleaning and lining
High
External corrosion - soil
Cathodic protection
Medium
External corrosion - other
Cathodic protection
Medium
Leadite corrosion
Replace the joint only
Low
Leadite expansion
Replace the joint only
Low
Material incompatibilities
Install dielectrics at corporation stops
Medium
Gasket deterioration
Replace the joint only
High
Additional information regarding some of the potential rehabilitation or prevention
strategies (e.g. cleaning and lining, cathodic protection) is discussed subsequently in this section.
B. Rehabilitation Technologies
Once a water main has been identified as failing to meet its service requirements, the
method of replacement or renewal should be considered. Currently, the majority of water main
replacement is performed using open-cut or open-trench methods. Conventional open-trench
construction is still the most frequently and cost-effective method of water main replacement in
the United States, and therefore, contractors are usually easy to find and locally available. For
-------
many water utilities, the practice is to install the new main in a trench parallel to the old main. In
some cases, removal of the old main in not worthwhile or necessary, and old, damaged water
mains are simply abandoned or given to electric or cable utilities. Because the old main is kept
in service until the new main is in place and ready for connection to the customers' service lines,
service interruptions are minimized. In those cases where the old main has to be shut down
before the new main is in place, bypass pipes can be laid to provide uninterrupted service to
customers.
Though popular, open-cut methods can create considerable inconveniences to customers,
businesses, residences, and traffic in the area. In some cases these inconveniences can also
become very costly. As a result, trenchless technologies have attracted the attention of the water
industry as an alternative to open-trench methods. Based on the site-specific main replacement,
trenchless technologies can frequently reduce both direct rehabilitation costs and the additional
financial and commercial costs associated with holes in the road.
For over 20 years, trenchless renovation technologies have been steadily increasing and
playing an increasingly important role in the wastewater and gas industries, and for many of
those utilities, it is now their method of choice. In the United Kingdom, where extensive
privatization of the water supply industry has greatly accelerated rehabilitation expenditures,
numerous trenchless techniques are in widespread use. There is; however, some reluctance on
the part of U.S. water utilities to use trenchless technologies due to their inexperience with the
technology and questions regarding the use of the materials in a potable water system.
Recently, the AWWA Research Foundation (AWWARF) and a number of AWWA
technical committees have evaluated alternative rehabilitation technologies for application in the
water utility industry and developed guidelines for those technologies that have a proven track
record within the industry. The following paragraphs will briefly describe the alternative
technologies that could be considered by American Water utility subsidiaries to successfully
rehabilitate water mains and identify conditions under which each technology can best be applied
within American Water.
Alternative rehabilitation techniques can be classified into three categories according to
their effect on the performance of the existing pipe. The three categories include: non-structural
systems, semi-structural systems, and structural systems.
1. Nonstructural Lining Techniques
One of the most common and effective renewal methods used in the piping industry is the
application of a non-structural protective lining on the interior of the water main. Nonstructural
lining systems are used primarily to protect the inner surface of the host pipe from corrosion and
tuberculation. They have no effect on the structural performance of the host pipe and have a
minimal ability to bridge any existing discontinuities, such as corrosion holes or joint gaps.
Hence, non-structural lining systems have minimal effect on leakage. Their use is indicated in
pipes that are structurally sound and leak tight at the time of lining and expected to remain so for
the foreseeable future. Examples of nonstructural techniques include cement-mortar lining and
epoxy resin lining. Statements regarding the effect of service connections, valves, bends, and
-------
appurtenances on efficiency and the expected service life extension from non-structural pipe
lining apply to both lining methods discussed.
The advantages of non-structural pipe lining are that a smooth protective non-structural
coating is applied to the interior surface of the pipe that restores hydraulic capacity to the water
main. A limitation is that service connections, valves, bends, and appurtenances will affect the
cost of lining projects. The expected service life of the pipe with reasonably good structural
condition can be extended 30 to 50 years with cement mortar lining or epoxy lining procedures.
Cement mortar lining is the most common rehabilitation technique in use today and is effective
and reliable. Cement mortar linings were first installed in existing pipelines using the centrifugal
process in the mid-1930s to rehabilitate pipelines. However, this method was limited to pipes
large enough for a person to enter. In the 1960s, remote lining processes were introduced.
Today, cement mortar is applied to new ductile iron pipes and most new steel pipes before
installation, making this method a standard in the water industry. Service lines and laterals less
than 2 inches in diameter must be cleared after the lining application. This is done about 1 hour
after the lining is completed, using compressed air to blow open the service line at the
connection to the main. Laterals over 2 inches are not plugged by centrifugal lining and do not
require excavation or blow back. Cement mortar lining may increase the pH of water and
therefore is not recommended for soft or aggressive water.
The process for in-situ epoxy resin lining of iron and steel pipelines was developed in the
United Kingdom in the late 1970's and has been performed in North America since the early
1990's. The process has been used effectively to rehabilitate old, unlined water mains. Epoxy
lining of water mains is also classified as a nonstructural renewal method. As with other lining
techniques, pipelines must be thoroughly cleaned and dried before application of the epoxy
lining. The epoxy resin is applied to the interior of the pipeline using a centrifugal method. A
spinning head is winched through the pipeline at a constant rate spraying a thin (1 mm) liquid
epoxy coating onto the inner wall of the pipe. The coating cures in 16 hours and provides a
smooth and durable finish resistant to mineral deposits and future tuberculation buildup. Several
epoxy-lining materials are currently approved for use in the potable water systems under
ANSI/NSF 61. Epoxy resin linings do not normally block service lines and laterals. They do not
affect the pH of the water and may be used for soft water supplies. Problems can occur if water
is accidentally introduced in the main during the lining process. The lining will be damaged and
may cure incorrectly, creating water quality problems. Mix ratio errors will also cause failures in
the lining.
2. Semi-Structural Lining Techniques
Semi-Structural renovation systems generally involve the installation of a thin plastics-
based lining tube that achieves a "tight fit" to the pipe wall. Since the stiffness of the liner is less
than that of the host pipe, all internal pressure loads are almost entirely transferred to the original
pipe. Such a lining is required only to independently sustain internal pressure loads at
discontinuities, in the host pipe, such as corrosion holes or joint gaps. Semi-structural lining
techniques are best suited for long transmission mains with few service connections and for
situations in which obstacles such as buildings, underground utilities, and railroads do not permit
the excavation of the old pipes. Mains with corrosion holes and leaks, which would not be suited
-------
for cement mortar or epoxy lining but that have not experienced structural failures (i.e. breaks),
are good candidates for semi-structural lining. Semi-structural liners do reduce the effective
cross-sectional area of the pipe. Therefore, post lining flow requirements must be considered
when deciding to slip-line. However, the reduction in the friction factor of the liner pipe as
compared to the old, unlined pipe should compensate for the reduced cross sectional area. In
addition, the flow rate will not be reduced by corrosion over time. The geometry of the unlined
pipe must also be considered, as liners generally do not turn well through elbows. Excavations
will be required at branch connections, bends and service connections in order to complete the
installation. Examples of semi-structural lining techniques include: slip-lining, close-fit slip-
lining and cured in place pipe lining
3. Structural Lining Techniques
Structural lining techniques are capable of sustaining a long-term (50-year) internal burst
strength, when tested independently from the host pipe, equal or greater than the Maximum
Allowable Operating Pressure (MAOP) of the pipe to be rehabilitated. Additionally, structural
linings have the ability to survive any dynamic loading or other short-term effects associated
with sudden failure of the host pipe due to internal pressure loads. Structural lining techniques
are sometimes considered to be equivalent to the replacement pipe, although they may not be
designed to meet the same requirements for external buckling or longitudinal/bending strength as
the original pipe.
Structural linings will be used in circumstances similar to those for semi-structural lining,
but their use is essential for host pipes suffering from generalized external corrosion where the
mode of failure has been, or is likely to be, catastrophic longitudinal cracking. Examples of
structural lining techniques include structural slip lining and pipe bursting. Structural slip-lining
techniques are similar to the semi-structural slip lining methods, but with varying design
parameters for the new pipe regarding wall thickness, pressure rating, and operating
requirements.
Pipe bursting is a patented process of replacing existing water mains by breaking and
displacing them and installing a replacement pipe along the same route and in the void created.
The pipe bursting technology is a total pipe replacement method. The pipe bursting process
replaces the original pipe with a new pipe of the same diameter or larger. The system consists of
a pneumatic, hydraulic or static bursting unit that splits the existing pipe while simultaneously
installing a replacement pipe of the same or larger diameter and pressure rating. The pipe-
bursting tool is designed to force its way through the existing pipe by fragmenting or splitting the
pipe and compressing the materials into the surrounding soil as it progresses. The use of high
density polyethylene pipes as the replacement pipe is desirable due to their flexibility, especially
when the pipes to be replaced are not straight. Pipe-bursting demonstrations using ductile iron
pipe have not been proven successful. All service connections should be completely
disconnected and isolated from the existing pipe before pipe-bursting operations begin. All
service connections, valves, bends, and appurtenances must be individually excavated and
connected to the new main. A temporary bypass system is usually provided to maintain service
to consumers. Breaking of existing repair clamps may also be a problem. If the pipe-bursting
heads cannot break a repair clamp, the pipe needs to be excavated and the repair clamps must be
-------
removed or cut with a pipe saw.
4. Cost Considerations
Compared to open-cut pipe replacement methods, the potential cost savings for
alternative rehabilitation methods are dependant on the minimization of site restoration activities
and the number of service connections on the existing main. All trenchless technologies require
excavations for insertion and receiving of pipes, and local excavations for service connections.
However, there are usually less excavations for alternative technologies than compared with
traditional open cut replacement methods. In order to avoid disruption of water supply to
customers, temporary service connections may be required to serve customers during the
construction period. Equipment and crew mobilization costs, length of mains being replaced,
and the "learning curve" all affect the unit cost of the alternative methods.
In order to satisfy the rehabilitation and replacement needs of water mains, it is essential
for the water utilities to consider alternative rehabilitation technologies along with traditional
open-cut technologies for cost-effective construction. Trenchless technologies will create less
disruption of public life than open-cut methods, although they may not be suitable for all pipe
rehabilitation and replacement. Key elements in the selection of a rehabilitation method are:
a. The exact nature of the problem(s) to be solved.
b. The hydraulic and operating pressure requirements for the rehabilitated main.
c. The materials, dimensions, and geometry of the water main.
d. The types and locations of valves, fittings, and service connections.
e. The length of time in which the main can be taken out of service.
f. Site-specific factors.
The selection of renewal technologies depends on pipe characteristics and site
characteristics as well as the techniques themselves. The aim of the selection process is to
consider all these factors to arrive at the most cost-effective, technically viable solution. Ideally,
the cost estimate should include not only direct contracting and related costs, but also indirect
costs associated with public disruption and longer-term maintenance. The most cost effective
technology can then be selected using present worth (PW) analysis or equivalent uniform annual
cost (EUAC) analysis. One approach to rehabilitation/replacement technique selection is
summarized in Exhibit No. 8. This chart provides a framework for selecting or rejecting groups
of techniques, depending on the nature of the performance problems, hydraulic requirements,
and some site-specific factors.
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Generally four types of problems (structural, hydraulic, joint leaks, and water quality)
need to be evaluated in determining the options available for the pipe. This evaluation is
performed in a hierarchical order, with the most critical pipe problems being addressed first and
any remaining problems associated with the pipe being addressed by default. The following pipe
problems should be evaluated when selecting renewal technologies:
a. If the problem is structural (loss of strength), the options are replacing the pipe
(same size or larger) or installing a structural liner. Using these options will also
address hydraulic, joint leak, and water quality problems.
b. If the problem is hydraulic (lack of adequate flow capacity) the options are
replacing the pipe (same size or larger) or installing a structural, semi-structural,
or non-structural liner provided the existing pipe diameter is adequate. Using
these options will also address joint leak and water quality problems.
c. If the problem is joint leaks, the options are replacing the pipe (same size or
larger), and installing a structural or semi-structural liner. Using these options
will also address water quality problems.
d. If the problem is water quality, the options are replacing the pipe (same size or
larger), and installing a liner. The lining can be structural, semi-structural, or
non-structural.
Once the pipe problem and available renewal options have been determined, the
applicable renewal methods should be selected based on pipe and site characteristic information.
Exhibit No. 9 lists a summary of the technologies discussed and recommended applicable use.
-------
Exhibit No. 9
Summary of Applicable Technology and Recommended Use
Tcchii<>loป>
Ki'cnmmciHk'ri Application
Cement Mortar Lining
Prevent scale formation, internal corrosion and reduce pipe roughness (improve
Hazen Williams C-value).
Considered with hydraulic and wq problems when there are no structural and joint
leaks and original pipe material is cast iron, ductile iron or steel.
Should not be considered when soft or acidic water is conveyed due to possible
deterioration of CML.
Epoxy Resin Lining
Protects original pipe against corrosion and provides an increased Hazen-
Williams C-value.
Considered with hydraulic and water quality (WQ) problems when there are no
structural and joint leak problems.
Conventional Slip Lining
Effective diameter of pipe is reduced, with a new pipe have a smooth interior
surface.
Excavations are required for service connections, entrance pits and exit pits.
Various pipe materials (DI, PVC, HDPE and steel) may be used as new pipe. No
strength is added to the host pipe in conventional slip lining.
Close-Fit Slip-lining
Classified as structural or semi-structural lining depending on the thickness of the
liner. The inserted pipe add strength, prevents further internal corrosion and
improves Hazen-Williams C-value.
Considered for hydraulic, joint leak and water quality problems with no structural
problems are involved.
Cured in Place Pipe
Compared to close-fit lining, the thickness of CIPP liner is typically less than a
close-fit liner.
As with the close-fit liner, the loss of diameter is compensated for by an improved
Hazen-William C-value.
As opposed to epoxy lining, CIPP also provides a certain measure of leakage
protection.
Considered a semi-structural liner and is applicable for hydraulic, joint leak and
water quality problems when no structural problems are involved.
Pipe Bursting
Pipe bursting is a structural lining technique and is considered suitable for CI,
PVC, AC and thin wall steel pipes.
Pipe Bursting recommended for deep mains with sufficient cover to avoid
heaving.
Host pipe should not have offset pipe joints or clamps with bolts.
Applicable for replacing pipes of the same diameter or larger.
Excavations are required for service connections, entrance pits and exit pits.
Generally, conventional open-cut methods would be the preferred method of main
rehabilitation. Installation of polyethylene encased ductile iron pipe has an anticipated service
life well over 100 years. However, when the situation (financial or technical) warrants the use of
an alternative technology, a potential cost savings may be realized. Industry and vendor cost
estimates for the various alternative technologies indicate a potential savings as follows:
a. Non-structural (cement mortar and epoxy lining) - 40%-60% less than
conventional open cut replacement.
b. Semi-structural (slip lining and close fit slip lining) - 30%-40% less than
conventional open cut replacement.
c. Structural (pipe bursting) - 20%-30% less than conventional open cut
replacement.
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Selecting the optimal solution to a specific pipeline problem is a complex process
involving both technical and economical considerations. AWWARF is currently developing a
computer-based decision tool to assist utilities in this selection process. The computer model is
expected to be published by AWWARF in the Spring, 2002 and will provide guidance to utilities
in considering the important criteria for selecting suitable technologies and pipe materials based
on present worth and environmental considerations. The computer model is expected to assist
utilities in selecting several renewal technologies that are appropriate for the pipe and site
characteristics of the associated project, allowing utilities to compare different technologies that
they may not have considered in the past.
C. Preventative Technologies
Cathodic Protection is a technology for reducing corrosion of a metal water main by
turning the entire main into the cathode of a galvanic or electrolytic corrosion cell. Normally,
sacrificial anodes are used as the galvanic cell to minimize the effects of external corrosion on
existing metal water mains, thus reducing water main breaks and extending the useful life of the
mains. A sacrificial anode system does not stop the process of corrosion but rather redirects the
corrosion from the water main to the anode. Exhibit No. 10 shows a typical installation of a
galvanic anode. Sacrificial anode protection may be used in selective "hot spot" (highly
corrosive soils) areas that have been located by soil-survey procedures. In corrosive soils,
sacrificial anodes should be installed during the repair of water mains. Typically this would only
increase the total cost of the repair by approximately $200 - $300 per break.
Exhibit No. 10
Anode Installation
Angered hole
Connection lo piping
As a preventative maintenance program, sacrificial anodes are typically installed at 40-
foot spacing (at every other joint) to be cost effective. This requires that rubber-gasketed joints
be electrically bonded along the protected water main. It is also recommended that test-
monitoring stations be installed at selected intervals along the water main to verify that the
-------
systems are operating as intended, to assess the break reduction efficiency and to monitor the
replacement timeframe for anodes.
D. Analysis of Distribution Pipe Materials for Future Use
In order to make recommendations regarding future pipe material usage, it is necessary to
understand the differences between each of the potential pipe materials. This investigation is
limited to "distribution size" materials (up to approximately 24") which includes ductile iron
(DI), polyvinyl chloride (PVC), and high density polyethylene (HDPE). Pipes larger than 24"
are typically evaluated on a case by case basis, and also include steel and concrete pipes which
are typically not cost effective in the smaller sizes. Exhibits No. 1 la, 1 lb, and 11c below list the
material properties, pipe properties, and operational considerations for each of the three types of
pipes.
Exhibit No. 11a
Comparison of Distribution Size Pipe Materials - Material Properties
Miilcriiil PmpcrO
1)1
PVC
iidpi:
Tensile strength
60,000 psi
7,000 psi
3,200 psi
Compressive strength
48,000 psi
9,000 psi
1,600 psi
Yield strength
42,000 psi
14,500 psi
5,000 psi
Ring bending stress
48,000 psi
none specified
none specified
Impact strength
17.5 ft-lbs/in
0.75 ft-lbs/in
3.5 ft-lbs/in
Density
441 lbs/ft3
88.6 lbs/ft3
59.6 lbs/ft3
Modulus of elasticity
24,000,000 psi
400,000 psi
110,000 psi
Temperature range
< 150ฐF
<140ฐF
-50 to 140ฐ F under press.
Thermal expansion
0.07" per 10ฐ F per 100'
0.33" per 10ฐ F per 100'
1" per 10ฐ F per 100'
Corrosion resistance (int)
Good - w/cement lining
Excellent
Excellent
Corrosion resistance (ext)
Good - w/polywrap
Excellent
Excellent
UV resistance
Excellent
Gradual strength decline
Yes - w/carbon black
Abrasion resistance
Excellent
Good
Good
Cyclic resistance
Excellent
Fair
Good
Permeation resistance
Yes
No - solvents &
petroleum
No - solvents &
petroleum
Scale & growth resistance
Good
Excellent
Excellent
The primary difference between the three materials is that DI is much stronger than PVC
or HDPE. However, DI is susceptible to corrosion which is not an issue with the other two
materials. PVC pipe is very similar to DI pipe in terms of installation, repair, and tapping, and
thus it was easy for water utilities, which had historically used cast iron pipe, to transition to
PVC pipe. HDPE is just starting to gain acceptance in the United States. It is flexible and less
brittle than PVC pipe, and has been popular in applications such as directional drilling, slip
lining, and pipe bursting. 70% of all new pipe installed in the United Kingdom is HDPE, and it
has successfully been utilized in that country for over 50 years. Gas utilities in the United States,
which have a much lower leak tolerance than water utilities, use HDPE almost exclusively.
However, since gas mains are typically smaller in diameter than water mains, the gas industry
also enjoys the advantage of purchasing 500' coils in the smaller sizes and eliminating the labor
associated with 10 joints. One of the main disadvantages of HDPE had been that it required
specialized equipment to create the joints. The size and weight of the machine required that the
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joints be fused above ground which could be difficult in congested areas. However, the
technology for heat fusing HDPE pipe has improved in recent years with the advent of
electrofusion couplings which can be utilized in the trench.
Exhibit No. lib
Comparison of Distribution Size Pipe Materials - Pipe Properties
Pipe i
1)1
PVC
iiDPi-:
Trade organization
DIPRA
Uni-Bell
ppi
AWWA designation
C151
C900 and C905
C906
Diameter range
3" - 64"
4" -12" (C900)
14" - 48" (C905)
4" - 63"
Pressure range
350 psi
100 psi - 200 psi
50 psi - 255 psi
ID range (8")
8.425"
7.76" - 8.33"
6.918"-8.136"
Wall thickness range (8")
0.25"
0.362" - 0.646"
0.265" - 1.182"
Weight range (8")
21.1 lbs/ft
6.6 lbs/ft -11.4 lbs/ft
5.1 lbs/ft -11.06 lbs/ft
OD nominal (8")
9.05"
9.05"
9.05"
Buoyant (8" 100 psi)
No
Yes
Yes
Surge allowance
100 psi
125 - 200% of press.
rating
None for 14" - 48"
(C905)
50 - 100% of press, rating
Surge potential (8" 100
psi)
53.6 psi per 1 ft/sec AV
17.6 psi per 1 ft/sec AV
9.8 psi per 1 ft/sec AV
Integrity under vacuum
Excellent
Good
Poor
C-factor
140
150
150
Standard pipe lengths (8")
18 ft or 20 ft
20 ft
40 ft or 50 ft
Type of joints
Push-on or mechanical
Push-on or mechanical
Heat fused
Max joint deflection (8")
5ฐ
3ฐ
Radius = 20-50 times
OD
Compatible w/DI fittings
Yes
Yes
Yes - inDI sizes
Exhibit
Comparison of Distribution Size Pipe
No. 11c
Materials - Operational Considerations
Opci'iilioiiiil ( onsirii'i'iilion
1)1
PVC
iiDPi-:
Ease of installation
Subjective
Subjective
Subjective
Can be direct tapped
Yes
Yes
No
Need for special installation
equipment
No
No
Yes
Need for special bedding for
typical installations
No
Yes
No
Need for joint restraint
Yes
Yes
No
Ability to locate underground
Excellent
Poor - needs tracer wire
Poor - needs tracer wire
Applicable for above ground
installations
Yes
With opaque material for
UV resistance
Yes - w/proper support
Applicable for aqueous
installations
Yes
Yes
Yes - but potential for
flattening is high
Anticipated service life
100 years
50 - 100 years
50 years
Although PVC and HDPE pipe have their place in the market and in specific areas of the
country, some concerns need to be considered. PVC in sizes 14" and greater is not designed
with a surge allowance. Another consideration is the design life of HDPE, which, per the
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manufacturers, is 50 years. Although PVC manufacturers state that their pipe has an estimated
100-year life (similar to DI), there are concerns similar to that of HDPE of strength reduction
over time due to cyclic loading. Relative life cycle costs should be considered when selecting
the best pipe material for both new and replacement mains.
IV. Value Added Management Strategies for Buried Infrastructure
This section presents and evaluates various management strategies for addressing the
challenges discussed in the previous sections. This includes broad based assessment methods
and a proposed performance based management approach.
A. Broad Based Infrastructure Assessment Methods
Broad-based assessment methods refer to those methods that provide an overview of the
replacement needs of a distribution system. In other words, they present the big picture as to the
condition of the system. Broad-based assessments typically include:
1. Accumulating basic historical information on the system's infrastructure (miles of
pipe in system, age of the pipe, and material of pipe).
2. Categorizing and analyzing this information.
3. Estimating life expectancies of the different types of mains.
4. Summarizing results.
Broad-based assessment methods help determine whether a utility is currently spending
enough capital on its infrastructure maintenance. These methods are forecasting tools that
predict future infrastructure replacement needs and can provide insight as to the appropriate level
of investment for the system. They help answer questions such as "how much pipe should be
replaced each year in the distribution system?" and "is the current expenditure level adequate, or
is the utility facing a major financial burden in the next few years?" Consequently, they can
provide guidance in helping to determine a utility's long-term capital investment plan to address
infrastructure renewal.
Two of the most prominent broad-based infrastructure models are KANEW and NESSIE.
Both models provide a forecast of the amount of infrastructure that will need to be replaced each
year over a future time period. KANEW provides results in terms of miles of main, whereas
NESSIE provides it in dollars. With just a limited amount of data that should be readily
available for most utilities, broad-based infrastructure assessment methods can provide a
reasonable estimate of the amount of pipe that should be replaced each year in the system, thus
providing a benchmark with which to compare current levels of spending. However, life
expectancies of mains are simply estimates provided by utility personnel. There is no
engineering or economic determination that supports these estimates; consequently, results are
very subjective. Such models do not identify or prioritize individual mains to be replaced.
Consequently, broad-based assessment models are useful, but alone are insufficient to manage
buried infrastructure.
B. Performance Based Buried Infrastructure Management Approach
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A performance based buried infrastructure management approach involves a detailed
inventory by pipeline segment and monitoring how well individual pipelines are meeting the
level of service that is required of them. This type of approach is more commonly used for
above ground infrastructure, and in particular, mechanical equipment which requires routine
preventative maintenance. Since buried infrastructure primarily consists of pipe which has no
moving parts and is not readily accessible, performance based management of these buried assets
has historically not been performed in the water industry. However, the following are reasons
for implementing such a plan:
a. Current infrastructure planning for water utilities primarily addresses pipe
replacement needs from a reliability and hydraulic standpoint. Another tool is
needed to complement this which will address pipe replacement needs from a
maintenance and customer service perspective.
b. Currently, pipe replacement decisions are made, for the most part, reactively.
Once a pipe stops providing the level of service expected of it, it is targeted for
replacement. A performance based management approach would allow for
proactive planning. For example, if specific vintages of pipe are reactively being
replaced at a high rate, proactive decisions can be made for similar vintages of
pipe exposed to similar operating conditions before they stop providing an
acceptable level of service to the customer.
c. It is the preferred approach of GASB 34, and is also recommended by the H2O
Coalition for private utilities that would potentially apply for federal assistance.
It is important to selectively identify the data that would be required in a performance
based management plan. If the data requirements are too high, it could hinder the
implementation of the plan and also put an unnecessary and costly workload requirement on the
utility. However, if the data requirements are too low, the information needed to make
appropriate and justifiable management decisions will not be available. Exhibit No. 15 outlines
the recommended data requirements for both existing infrastructure and new infrastructure. This
data is broken down into physical, performance, and commercial/service information. The
requirements for existing and new infrastructure are different since certain historical data may
simply not be available, or the effort to acquire the historical information could not be justified
when considering the additional value it would provide in making informed management
decisions.
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Exhibit No. 15
Data Requirements for a Detailed Management Plan
Plnsiciil
r.xisl
New
PeiToniiiinee
r.xisl
New
('ommerci;il/Ser\ ice
I'.xis
I
New
Year of Inslallalion
Y
Y
CoiiiplainL Frequency
A
Y
Ci'ilical Cuslomei'
Y
Y
Diameter
Y
Y
Type of Complaint
A
Y
Affect on Community
Y
Y
Material
Y
Y
Break Frequency
A
Y
No. of People Served
A
A
Length
Y
Y
Type of Break
A
Y
Length of Shutdown
A
A
Location
Y
Y
Reason for Break
A
Y
Coordination w/Others
A
A
Interior Lining
A
Y
Service (hydraulic)
Adequacy
Y
Y
Exterior Protection
A
Y
Fire Flow Adequacy
Y
Y
Joint
A
Y
Wall Thickness
A
Y
Soil conditions
A
A
Internal Condition
A
External Condition
A
Y = yes, in all cases
A = as needed, or as available
It is necessary to know specific physical information for all existing and new buried
assets as identified in the first set of columns in Exhibit No. 15. It is not possible to manage the
assets without knowing the basic "what, where, and when". Tracking additional information,
which is available for new installations but might not be readily available for existing assets, is
useful in understanding service characteristics and potential deficiencies associated with the pipe
and what remedial actions could potentially be considered. Although this information may not
have been recorded at the time of installation, much of it can be obtained when performing
maintenance on the pipe. One important physical parameter that warrants additional discussion
is the "length" of the main. Length is defined as a section of main which has similar physical,
operational, and commercial/service characteristics that can be isolated in the field. It does not
necessarily correlate exactly with the work order under which the main was installed since the
diameter or other property might not be the same for the entire length. To simplify the data
requirements, the specified length of main should be as long as possible, and relate to the street
on which it is installed, if possible.
Regardless of what is physically located in the ground, the performance information, as
defined in the middle set of columns in Exhibit No. 15, is the most important to know. Decisions
on the need for maintenance or replacement of a pipe should be based solely on how the pipe
performs. Similar types of pipes in different operating conditions will perform differently. For
example, a thin walled spun cast pipe operating under low pressure and installed in non-
corrosive soil may provide considerably longer service than one operating at a higher pressure in
corrosive soils. Pipes should remain in service, regardless of their physical attributes, until they
stop providing the level of service that is expected of them, or until it can be proactively
predicted that they will soon stop providing this level of service.
Commercial/Service aspects of the pipe performance, as defined in the last set of columns
in Exhibit No. 15, provide a further distinction on the importance of the performance parameters.
Factoring this aspect into a performance based management plan results in more intelligent
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decision making. Defining the "level of service" that is expected from a pipe is dependant on the
specific customers that it is serving. For example, a relatively low main break frequency may be
acceptable in most instances; however, if the main is serving a critical customer, such as a
hospital, or would have a great impact on the community (such as closing down a major road),
even a low break frequency may not be tolerable. Other information, such as coordination with
municipal work (e.g. street paving) is also important to factor into any decisions regarding pipe
maintenance vs. replacement.
In order to prioritize the mains which should be targeted for replacement, rehabilitation,
or preventative measures, a rating system is needed. In developing such as system, it is
important to only rate the variables which pertain to the basic question - "is the main providing
the level of service that is expected of it?". Referring back to Exhibit No. 9, this would include
the following four performance variables:
Complaint Frequency
Break Frequency
Service (hydraulic) Adequacy
Fire Flow Adequacy
The other three performance variables - Type of Complaint, Type of Break, and Reason
for Break - are useful in determining how to address the potential lack of adequate service being
provided by the main, and would factor into decisions such as whether to replace or to
rehabilitate the main.
Simply rating each of these four operational variables; however, does not fully address
the issue of "level of service" since the necessary level of service can vary for each main as
previously discussed. For this reason, all of the commercial/service variables defined in Exhibit
No. 15 also need to be included in the rating system. These variables are as follows:
Critical Customer
Affect on Community
Number of People Served
Length of Shutdown
Coordination with Others
Although the physical information is not included directly in the rating system, it is still
extremely useful in making ultimate decisions regarding the need to replace mains. However,
attempting to include it in the rating system could skew the results. For example, if a rating were
provided for the type of joint, all leadite joints would receive the worst rating since they have
historically performed poorly in the industry. However, if these joints are performing well at a
specific location under specific operating conditions, why "penalize" that main by giving it a
poor rating simply based on the physical properties of the joint and not its performance?
Another example would be year of installation (i.e. the age of the pipe). Many mains in this
country that were installed in the 1800's continue to provided adequate and reliable service, and
again, there is no need to skew the rating of a pipe by arbitrarily including this information in the
rating system. However, this information can and should ultimately factor into the final
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decisions regarding pipe replacement once the rating system, which is based on performance and
commercial/service variables, identifies those critical mains which need attention. For example,
if two mains score equally poor in the rating system (based on performance), and one has leadite
joints and is older than the other main, then that information should be brought into the final
decision making process and considered at that time.
C. Data Management
There are three options to consider for maintaining the data that is recommended for a
detailed management plan. The first option would be to utilize a simple personal computer
spreadsheet or database. Although this would be the least costly solution, it would also be the
most labor intensive. An important factor when implementing a computerized program is to
assure, where possible, that the required data is entered in the course of doing daily business (a
self populating database) thus minimizing duplication of data entry. A personal computer
spreadsheet or database would likely not meet this criteria.
The other two software options would utilize either an infrastructure management
software package or a computerized maintenance management system (CMMS). The two are
similar, and vary mainly in that infrastructure management software is typically less flexible and
more specifically geared to the municipal market, whereas CMMS software is more powerful
and more customizable (and ultimately more costly). Again, the key with either is that they
integrate with other software currently utilized by the utility and that they meet the needs of other
operations, customer service, and maintenance tasks in addition to buried infrastructure
management. For example, if a new main is being installed, and information is being entered
into a utility's asset management system, this information needs to populate the database selected
for use in managing buried infrastructure. A customer complaint that is recorded in a Customer
Information System would be another example of information that needs to link with the buried
infrastructure software. The other advantage that these types of software packages have over
simple spreadsheets or databases is that they allow integration with Geographical Information
System (GIS) software. The value of GIS is that it provides the necessary geographical
information which should factor into decisions regarding pipe replacement. For example, if
main replacement is warranted in a particular geographical area, it might be appropriate to
replace other mains in the area to avoid future disruption to the customers and the community.
Without GIS, it would be difficult to perform the same type of evaluation except possibly in very
small systems.
V. Implementation
a. Data Collection & Buried Asset Inventory. The data necessary for a performance
based management plan (see Exhibit No. 15) can be found in a variety of places
that would include:
Distribution drawings
Work orders
Asset records
Customer Information Systems
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Maintenance records
Tapping records
As a last resort, information such as material type could be estimated based on
information provided in Exhibit No. 2 of this report.
b. Integrated Buried Asset Inventory and Performance Monitoring and Reporting
System: Formulate the systematic process for tracking performance variables for
individual pipeline segments included in the Buried Asset Inventory. Develop a
system that allows the review of pipeline segment performance in conjunction
with the commercial/service importance of the main. The need for geographical
interface (GIS) should also be considered. The ability to query, select, sort, and
prioritize buried asset information, based on multiple selection criteria, is needed
to facilitate decision making.
c. Training and Education: Formal training is important to address relevant
technical issues such as hydraulic transients, pipe failure mechanisms, operational
strategies for reducing or eliminating pipe failures, and pipe rehabilitation
techniques. The data collection needs and the importance of maintenance activity
feedback should be covered.
Conclusions
a. The industry's assessment of buried infrastructure needs appears to be reasonable
although health risks have not factored into the analysis to date.
b. Utilities have begun addressing the issue, although primarily with a reactive
approach. A pro-active, uniform, and systematic approach would be more
efficient. The current level of investment may be inadequate.
c. Direct costs (repair vs. replace) will not drive the decision making process. Health
risks, commercial and service impacts must be considered. The appropriate time
to replace or rehabilitate a main is when it stops providing the level of service that
is expected of it. This requirement will vary, even within the same physical
system.
d. Operational strategies, rehabilitation technologies, and preventative technologies
have merit and should be considered in the decision making process.
e. Broad based assessment methods are useful planning tools but are not adequate to
use as a management tool.
f. A performance based management plan is valuable, and integration with
operations and information management strategies is essential.
g. A prudent and systematic management process will better serve a utility in the
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support of capital investment needed to properly replace or rehabilitate
distribution systems.
h. "Knowing your system" and organizing the data is the first and most critical step
in any buried infrastructure management approach.
i. Training and education of personnel regarding technical issues associated with
buried infrastructure is critical. Specifically, the technical content would include
hydraulic transients, pipe failure mechanisms, operational strategies for reducing
or eliminating pipe failures, pipe rehabilitation techniques, and corrosion control.
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VII. References
1. AWWA (American Water Works Association). 2001. Rehabilitation of Water
Mains. Manual of Practice M28. Denver Colorado: AWWA.
2. AWWA (American Water Works Association). 1987. External Corrosion -
Introduction to Chemistry and Control. Manual of Practice M27. Denver
Colorado.: AWWA.
3. AWWA 2001 Annual Conference. The Water Main Rehabilitation Workshop.
AWWA.
4. Deb, Arun K., Yakir J. Hasit, and Chris Norris. 1999. Demonstration of
Innovative Water Main Renewal Techniques. Denver, Colo.: AWWA Research
Foundation and American Water Works Association.
5. Heavens, Dr. John W.. [No Date], The Trenchless Renovation of Potable Water
Pipelines. [Online] Insituform Technologies, Inc. Available:
< http://www.insituform.com/resourceroom/rr2 03.pdf >. [cited August 20, 2001 ]
6. TT Technologies Inc. 1999. Technical Brochure on Pipe Bursting [Online],
Available: < http://www.tttechnologies.com > . [cited August 21, 2001]
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Corrosion of Existing Ductile Iron Water Mains Within the Region of Durham",
a report prepared by the Technical Support Works Dept., Region of Durham,
January, (1999).
8. Szoke, Nicholas T., Diane Sacher, Len Chambers, Grant Firth. 2001. Full Scale
Implementation of Cathodic Protection of Metallic Watermains. AWWA 2001.
Infrastructure Conference Proceedings.
9. Corrpro Companies, Inc. 1999. Synopsis - Corrpor's BRLEsm Program. BRLEsm
Break Reduction / Life Extension for Cast and Ductile Iron Water Mains.
10. Uni-Bell PVC Pipe Association. [No Date], Installation Guide for PVC Pressure
Pipe [Online], Available: < http://www.uni-bell.org > [cited September 5, 2001]
11. Uni-Bell PVC Pipe Association. 2001. Handbook of PVC Pipe Design and
Construction. Dallas, Texas.
12. Ductile Iron Pipe Research Association. Handbook of Ductile Iron Pipe. Sixth
Edition, 1984.
13. Environmental Protection Agency (EPA). Drinking Water Infrastructure Needs
Survey. Second Report to Congress. February, 2001.
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14. Water Infrastructure Network (WIN). Water Infrastructure NOW. February,
2001.
15. American Society of Civil Engineers (ASCE). Report Card for America's
Infrastructure. 2001.
16. Roy F. Weston, Inc. Development of a Water Main Replacement Management
Plan. May 31, 2000.
17. PA Consulting Group. The Nessie Model. 2001.
18. American Water Works Association Research Foundation. Quantifying Future
Rehabilitation Needs of Water Mains. 1998
19. Governmental Accounting Standards Board (GASB). Statement No. 34. 2001.
20. Kielty, Dick. Corrosion of Buried Cast Iron Pipelines. American Engineering
Testing, Inc. Summer 1998.
21. Makar, J.M. A Preliminary Analysis of Failures in Grey Cast Iron Water Pipes.
National Research Council of Canada.
22. Ductile Iron Pipe Research Association. Ductile Iron Pipe General Information.
< http://www.dipra.org >
23. ISCO Industries. HDPE Pipe. < http://www:isco-pipe.com >
24. Snoeyink, V., and I. Wagner. 1996. Internal Corrosion of Water Distribution
Systems. AWWARF and TZW. Denver, Co.
25. Benjamin, M., H. Sontheimer, P. Leroy. 1996. Internal Corrosion of Water
Distribution Systems. AWWARF and TZW. Denver, Co.
26. Leroy, P., M. Schock, I. Wagner, and H. Holtschulte. 1996. Internal Corrosion of
Water Distribution Systems. AWWARF and TZW. Denver, Co.
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