Where do you place the anodes?
Machine Design , January 12, 2006
GALE|A14415379 Where do you pla Machine Design
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January 12, 2006
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Cathodic protection (CP) is a simple method for actively protecting a metallic structure. In concept, a
shipbuilder for example, would place anodes about the hull and drive them with a low current. This is an
impressed current, cathodic-protection system or ICCP. Its goal is to supply sufficient current to the
uncoated hull sections to prevent them from corroding. Several critical design issues include determining
the location of the anodes relative to the hull and estimating the current output required to protect the
ship.
Developers at Beasy, Billerica, Mass. (beasy.com), say their analysis software assists by letting designers
develop 3D computer prototypes of the vessel and CP system. These models let engineers assess the
performance of both sacrificial anode and active ICCP systems. Users can vary parameters such as
anode location, their number, and current to develop an optimum system. It also lets engineers
investigate interference effects caused by nearby CP systems, electrical sources, docks, pipelines, and
other metallic structures.
CIRCLE 622
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Full Text: COPYRIGHT 2006 Penton Media, Inc., Penton Business Media, Inc. and their subsidiaries.
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Source Citation:
"Where do you place the anodes?" Machine Design 12 Jan. 2006: 131. Gale Science In Context. Web. 4 Oct.
2011.
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Save our cars
New Scientist , September 1, 2007
GALE|A16873870 Save our cars
New Scientist
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Full Text: COPYRIGHT 2007 Reed Business Information Ltd. For more science news and comments see
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Source Citation:
Fowler, Pete. "Save our cars." New Scientist 195.2619 (2007): 73. Gale Science In Context. Web. 4 Oct.
2011.
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Gale Document Number: GALE|A168738709
Impacts of cathodic protection on pipe break
probabilities: a Toronto case study
Canadian Journal of Civil Engineering , February 2008
GALE|A18040395 Impacts of cathod Canadian Journal
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February 2008
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Abstract: The pipe break database of the Greater Toronto Area (GTA), dating from 1960, is used to
quantify the impacts of cathodicprotection (CP) on the frequency of pipe breaks. The findings
demonstrate that the average time between pipe breaks increases by up to an average of almost 4 years
for ductile iron pipes after CP is placed on a pipe. Further, the probability of a pipe break occurring 10
years after the application of CP decreases in comparison with pipes that have not been cathodically
protected. The cost savings for CP are substantial, with the repair costs (including the cost of CP
implementation) decreasing to one-third for ductile iron (DI) pipes of 150 mm diameter and to one-half for
DI pipes of 300 mm diameter. The cost savings for cast iron (CI) pipes are not as dramatic, but still
demonstrate a reduction to 60% of the repair costs for 150 mm diameter pipes and to 70% of the repair
costs for 300 mm diameter pipes.
Key words: pipe breaks, cathodic protection, probabilistic model, municipal infrastructure.
Resume : Datant de 1960, la base de donnees sur les bris de conduites de la Grande Region de Toronto
est utilisee pour quantifier les impacts de la protection cathodique (PC) sur la frequence des bris de
conduites. Les conclusions montrent que le temps moyen entre les bris de conduites augmente et est
rendu a une moyenne de presque quatre ans pour les conduites en fonte ductile une fois que la PC est
installee. De plus, la probabilite d'un bris de conduite survenant 10 ans apres l'implantation diminue si on
la compare a celle des conduites qui n'ont pas ete munies d'un systeme de protection cathodique.
L'economie realisee avec la protection cathodique est importante : les couts de reparation (incluant le
cout d'implantation de la protectioncathodique) ont diminue au tiers pour les conduites en fonte ductile de
150 mm de diameter et a la moitie pour les conduites en fonte ductile de 300 mm de diametre. Les
economies pour les conduites en fonte ductile ne sont pas aussi importantes mais demontrent tout de
meme une reduction a 60 % des couts de reparation pour les conduites en fonte ductile de 150 mm de
diametre et a 70 % pour les conduites en fonte ductile de 300 mm de diametre.
Mots-cles : bris de conduites, protection cathodique, modele probabiliste, infrastructure municipale.
[Traduit par la Redaction]
Introduction
During recent decades, substantial efforts have been made to understand the implications of aging
municipal infrastructure. In particular, the deterioration of hydraulic capacity as well as the breakage
frequency of water distribution pipes have become significant and growing concerns. The seriousness of
the rate of aging of the infrastructure is apparent where, for example, it is noted that the greater Toronto
area (GTA) water distribution infrastructure has been aging at an average rate of just over 7 years per
decade, since 1930. Average rates of aging of water distribution infrastructure in various sectors of the
GTA include 8 years per decade in York, 8.6 years per decade in East York, 5.9 years per decade in
Scarborough, and 6.9 years per decade in Etobicoke. Hence, the aging of water infrastructure in the GTA
(and elsewhere in North America) is a very real phenomenon.
As an indication of aging infrastructure problems, failures of water distribution piping in the GTA are
occurring at the rate of between 25 and 30 breaks per year per 100 km of pipe for their 5500 km of
watermains, or a total of approximately 1600 breaks per year. A summary of the pipe breaks in the GTA
by sector is presented in Table 1. Using Scarborough as an example, these results show that 48% of the
pipe inventory in Scarborough has broken and 12635 pipe breaks have occurred since 1960 or, in other
words, each pipe within the network that has broken, broke approximately four times on average. This
rate of pipe breakage is more than double the average rate for Ontario municipalities and is a result of
increasing infrastructure age, pipe material, and urban form (City of Toronto 2006). However, it
demonstrates the severity of the pipe breakage issue in Ontario.
In 2006, the GTA addressed the aging and deteriorating infrastructure via the State of Good Repair
program. The program was allocated 71% of the 2006 gross budget for water and wastewater in the City
of Toronto and included projects such as replacement of 35 km of watermains and the cleaning and
relining of 114 km of pipes. The City has also implemented a 5-year capital plan that is investing in the
maintenance of aging water and wastewater infrastructure, as well as in the expansion for new
development. It is estimated that the plan will invest CAN$2.6 billion over the designated 5-year period
(City of Toronto 2006). Such expenditure levels are consistent with the engineering profession where, for
example, a recent US Environmental Protection Agency (EPA) survey estimated the costs for upgrading
water distribution systems in the USA at US$77 billion over the next 20 years (Davies et al. 1997).
Given the frequency of pipe breakage and aging of the municipal infrastructure, improved asset
management models have real value. As an initiative, Schuster et al. (2006) developed a probabilistic
pipe break model derived from the GTA inventory database. Statistical analyses of the historical pipe
break database provide probabilities for future pipe breakage (e.g., the probability of a pipe break
occurring within the next 10 years, given the pipe is cast iron, in silt and clay, is currently 10-years old,
and has not broken yet). When considering the costs and social impact arising from pipe breakage with
respect to asset management decision making, an important option is the provision of cathodic protection
(CP) of the water distribution pipes. This paper extends the work of Schuster et al. (2006) by analyzing
the changes in pipe break frequency arising from the application of CP. This type of approach is
recognized by Kleiner and Rajani (2000), who state that "identifying watermain breakage patterns over
time is an effective and inexpensive alternative to measure[ing] the structural deterioration of a water
distribution system."
Background
It is necessary to improve the understanding of pipe break frequency and to identify possible means of
reducing this frequency as such breaks cause both direct costs associated with repair or replacement of
pipes, as well as indirect costs such as economic impact on businesses located in the vicinity of the
break, as well as inconvenience to commuters having to detour around the region of a break. In the case
of failures in large pipes, or complications as a result of a break, the duration of construction may be
significant. For example, on 23 January 2005, a watermain break under Bay Street in Toronto resulted in
a flooded electric transformer station, cutting power supplies to the city centre (Rusk 2005). On 26 April
2006, a watermain break washed away part of Sheppard Avenue West in Toronto, resulting in indefinite
road closure to undertake repairs, and hundreds of people without water (Rush 2006). Furthermore, pipe
breaks represent a major potential source of contamination ingress into the drinking water system, and
such ingress may result in health impact on consumers. This is particularly problematic as the distribution
system is beyond the last point of water treatment, and hence, any contaminant incursion into the
distribution system that overwhelms or is unaffected by the chlorine residual is transported directly to
consumers for ingestion-inhalation-absorption.
To respond to the issues mentioned above, there is merit in increasing the understanding of pipe failures,
especially causative features and ways to decrease the frequency of pipe breaks. In particular, pipe
corrosion is a significant contributor to failure in both cast iron (CI) and ductile iron (DI) pipes. Failure
analyses have been used to quantify the past behavior of pipe failures, in terms of failure rates and interfailure times, to examine reliability and remaining life by a number of researchers including Shamir and
Howard (1979), O'Day et al. (1986), Clark et al. (1988), Andreou et al. (1987), and Gustafson and Clancy
(1999). Male et al. (1990) addressed the structural deterioration of water mains but did not consider the
combined hydraulic capacity. A pipe that is scheduled for relining due to inadequate hydraulic capacity
may be better replaced if its breakage frequency is expected to rise significantly in the future. The
challenge is, in part, to determine the most appropriate plan, in terms of pipe replacement versus
rehabilitation versus repair, as breakage is incurred.
As a means of decreasing breakage frequency, several different mechanisms have been employed to
slow down or prevent external pipe corrosion. Use of CP is one such measure, and can be undertaken at
the time of pipe placement in the ground or retroactively, by making "the metal a cathode by means of an
impressed direct current or attachment to a sacrificial anode (usually magnesium, aluminum, or zinc)"
(MACE 1984).Cathodic protection has been used in the GTA since 1986, in response to the frequency of
pipe breaks and the extensive number of DI pipes in its water distribution system. Almost 60% of pipes
that now have CP were protected between 2000 and 2005. with CP being implemented in 30% of those
pipes in 2003 alone.
Determining the appropriateness of implementation of CP involves evaluating the cost of tradeoffs
between the known costs of CP application versus the unknown timing of pipe repair due to breakage.
Use of CP costs CAN$50/m up to a diameter of 150 mm, increasing to CAN$100/m for 300 mm and
CAN$400/m for 1200 mm diameter pipes. Replacement, on the other hand, costs CAN$650/m for up
tol50 mm, CAN$1150/m for 300 mm, and CAN$2950/m for 1200 mm diameter pipes (City of Toronto
2006).
Use of CP has been demonstrated to reduce the number of breaks in water distribution systems
(Gummow 1988; Doherty 1990; Green et al. 1992). Shymko (2) (Rajani and Kleiner 2003) found that a
CP program in Durham, Ontario, significantly reduced water main breaks, although actual reductions
varied according to the type and location of the mains. In Winnipeg, it was demonstrated that CP
accounted for more than 17% of the reduction in pipe break frequency (Rajani and Kleiner 2003). Kroon
et al. (2006) state that a maximum 0.07 V polarisation can result in a 75% reduction in the corrosion rate
of DI pipes. Kleiner and Rajani (2004) reported that the effectiveness of CP depends not only on the
varying conditions under which it is implemented, but also on when it is applied.
Case study scenarios
The database for this research was provided by the Water Infrastructure Management group within the
City of Toronto. For purposes of this study, data were used from North York, York, Scarborough, and
Etobicoke, all part of the GTA. The database consists of address, year placed in ground, pipe material,
pipe length, pipe diameter, soil type, date of pipe breaks, and the date CP was applied. Pipe break data
were only recorded by GTA post-1960, and hence, to establish with certainty that the first break in the
record was actually the first pipe break, the analyses were limited to pipes laid in the ground in 1960 or
later. The final database consists of 112 entries for East York, 260 entries for York, 3264 entries for
Scarborough, and 2246 entries for Etobicoke. A total of 978 CI and DI pipes, in both sand and gravel and
silt and clay soils, have had CP applied to them. The number of pipes that have CP in any given region
varies considerably, with Etobicoke having less than 1% of its pipes with CP, and Scarborough having
close to 26%.
Pipes placed in sand and gravel have not generally been considered for CP, although some DI pipes
have been cathodically protected in the City of Toronto when the individual pipes have experienced a
significant number of breaks. Instead, implementation of CP has primarily been in pipes within silt and
clay soils, as these soils are generally more corrosive than sand and gravel types (Doyle et al. 2003). The
American Water Works Association (AWWA) has developed a soil corrosivity scale to determine when to
apply CP to a pipe. If the soil score is 10 or more, then the pipe requires CP or another type of protection.
Points are assigned based on soil resistivity (the lower the resistivity, the higher the number of points), pH
(the lower the pH, the greater the number of points), redox potential (the lower the redox potential, the
greater the number of points), and the presence of sulfides, and drainage conditions (poor drainage
conditions score more points). Soil resistivity is given the most weight in the scale, with a resistivity of<
700 [OMEGA]/cm scoring 10 points.
Nevertheless, while desirable, the necessary information is not always available to provide guidance, and
problems arise when attempting to incorporate environmental information into a model based on historical
information. A recent study by Wood and Lence (2006) suggests that utilities are only now beginning to
collect comprehensive data on pipe breaks. Further, environmental data are least likely to be collected,
and yet these data are highly significant to improve pipe break models.
Probabilistic model of pipe breakage
Based on recorded incidents of pipe breakage within the GTA between 1960 and 2004, the impact of CP
on pipe break incidence and probable failure rate for future breaks was determined by analysis of in situ
records. For the pipe break model, the probability (P) of pipe breakage is
[1] [P.sub.k](t, n) = [X.sub.k,t](n)/[J.sub.k]
where t = 1, ... m time periods since pipe placement in the ground (assumed for purposes herein that
each period is 5 years in duration); n = 1, ... N is the number of pipe breaks within an individual pipe since
placement in the ground; k represents the different pipe materials; (e.g., k = 1 for CI, k = 2 for DI);
[X.sub.k,t](n) is the number of pipes of type k, broken for the nth time, up to and including within time
period t [e.g., [X.sub.2,3](1) is the number of DI pipes that broke for the first time within the period of 10 to
14 years after placement in the ground], [J.sub.k] is the total number of pipes of type k placed in the
ground.
For n = 1 (first break) of pipe material k, up to and including t = 2 (i.e., between 5 and 9 years after
placement of the pipe in the ground), the probability of pipe breakage can be calculated as
[2] [P.sub.k](2, 1) = [X.sub.k,2](1)/[J.sub.k]
and for n = 2 (second break):
[3] [P.sub.k](2, 2) = [X.sub.k,2](2)|[X.sub.k,2-L]/[J.sub.k]
where [for all] L = 1, ... number of 5-year time intervals up to t.
The pipe break database for the GTA is used to determine the probability (eqs. [1] through [3]) for varying
t, n, and k.
Application of the model
Previous analyses (Schuster et al. 2006) demonstrated that, in general, silt and clay soils, as opposed to
sand and gravel soils, result in the greatest likelihood of first failure at earlier times, especially for smaller
diameter pipes. In particular, CI pipes are more prone to a first failure than other pipe materials [i.e., the
probability of an early first break is higher in CI than asbestos cement (AC), DI, or polyvinyl chloride
(PVC) pipe materials]. Once a pipe has failed, the probability of a second failure occurring soon after is
high. The highest rates of failure vary according to multiple factors, including pipe material, diameter, and
soil type. For example, it was identified that 150 mm diameter CI pipes in silt and clay soils are more likely
to break when compared with 100 and 250 mm diameter pipes of CI, DI, AC, or PVC in either silt and clay
or sand and gravel soils. Consider now the influence of CP on pipe break frequency. Figure 1 illustrates
the number of breaks following application of CP for CI and DI pipes in different soil conditions. For
example, 18% of DI pipes in sand and gravel had CP applied after the sixth break had occurred. Another
10% of the DI pipes in sand and gravel had CP applied after the seventh break. Similarly, 8% of DI pipes
in silt and clay had CP applied after the first break. These results show that the pipes to which CP was
applied were in various states of deterioration, with varying pipe-break history.
Table 2 summarizes the time period between breaks in the GTA, pre-CP versus post-CP. Table 2 shows
that average breaks per year decrease significantly after CP is applied. For example, DI pipes in silt and
clay average 0.06 breaks per year prior to CP, and occur only at the level of 0.01 per year after CP. The
average time between breaks for both CI and DI pipes in silt and clay soils and DI pipes in sand and
gravel soils increases post-CP. For example, the average time between breaks in DI pipes placed in silt
and clay increases from 2.26 years pre-CP to 6.14 years post-CP (fifth column in Table 2), or a 4-year
improvement. The implication of different soil types is also apparent; the average time between breaks is
slightly lower for pre-CP DI pipes in sand and gravel (1.98 years) versus silt and clay soils (2.26 years),
as shown in the fourth column of Table 2. Post-CP, the DI pipes placed in sand and gravel soils have a
longer period between breaks compared with those placed in silt and clay soils (7.50 years versus 6.14
years, as shown in the fifth column of Table 2).
[FIGURE 1 OMITTED]
Figure 2 depicts, in summary form, the average time between breaks for DI pipes in silt and clay, both
pre- and post-application of CP; for almost all categories, the time between breaks post-CP is higher than
pre-CP. This is especially noticeable for the length of time between the fourth and fifth breaks. For preCP, the time between the fourth and fifth break is less than 2 years, whereas for post-CP, it is more than
10 years between the fourth and fifth break. The exception is the time between the sixth and seventh
breaks, which is slightly higher for pre-CP pipes than post-CP. In both cases, breaks occur frequently
(less than 2 years apart).
The probabilities of pipes breaking within a specified time period was determined for CP and non-CP
pipes, as listed in Tables 3 and 4, respectively. Tables 3 and 4 list the probabilities that pipes of a
selected material in a specific soil type will break in the next time period (increasing by 5year increments).
Table 3 lists the probabilities of breakage for CI and DI pipes that have had CP applied. It indicates that
the probability increases with time and that CI pipes have a greater probability of breakage than DI pipes
(e.g., a 15% likelihood that CI pipes broke for the first time in the next 15 years, whereas only an 8% such
likelihood for the DI pipes, for the same silt and clay soil conditions). Table 4 demonstrates the same
probabilities for pipes located in Etobicoke, without CP.
Table 3 shows the probability of a DI pipe with CP in silt and clay breaking in the next 5 years is 0.06 (i.e.,
if CP is applied to a pipe, it has a 6% chance of breaking in the next 5 years). This information can be
used as part of budget planning for pipe repair costs on an annual basis (the expected values and the
95% range of costs for pipe repair that might be incurred) and further, can be used to establish tradeoffs
to determine whether the cost of placing CP on pipes is justified. Specifically, the probability of a pipe
break occurring within the next 10 years decreases significantly with the application of CP to pipes [e.g.,
the probability of a DI pipe placed in silt and clay breaking in the next 15 years is 0.14% (Table 4),
whereas if CP has been applied, this probability is almost halved to 0.08% (Table 3)]. Similarly, for CI
pipes in silt and clay, the probability of a break in the next 15 years is 0.34% (Table 4), but once CP has
been applied, this is reduced to 0.15% (Table 3).
[FIGURE 2 OMITTED]
The cost savings of CP can be quantified by applying typical CP and repair costs to 100 pipes with
lengths of 10 m and diameters of 150 and 300 mm, given average annual pipe break rates pre- and postCP (Table 2). The cost of repair of a pipe break is approximately CAN$5000 (3) and the cost of CP is
CAN$50/m for 150 mm pipes and CAN$100/ m for 300 mm pipes. The costs of pipe repair over a 10-year
period for DI, 150 mm, non-CP pipes is CAN$300000 as per Table 5. Over a 10-year period, the overall
repair costs for pipes with CP represent only one-third of the non-CP repair costs for 150 diameter pipes
(CAN$100 000 versus CAN$300000), and one-half the non-CP repair costs for 300 mm diameter pipes
[Table 5 (CAN$150 000 versus CAN$300000)]. A similar comparison using CI pipes (Table 6)
demonstrates savings where the cost of CP and repair represent approximately 60% of the cost of repair
in the absence of CP for 150 mm pipes, and a reduction to approximately 70% of the repair costs for 300
mm pipes.
From the results presented in Tables 5 and 6, it is apparent that there is a benefit from applying CP to
water distribution pipes, particularly for DI pipes. It is also noted that the preceding analyses could be
refined with knowledge of the soil resistivity.
Conclusions
A large historic database from the GTA allowed for analyses of the trends in pipe break occurrence ,
demonstrating the effectiveness of cathodicprotection (CP) on pipe break reduction and thus improved
asset management. For DI pipes in silt and clay, there was an increase between breaks from 2.3 to 6.1
years. Examples of the cost savings for DI pipes indicate that the application of CP on these pipes
reduces the total costs of repair to one-third that of non-CP 150 mm diameter pipes, and one-half the
costs of non-CP 300 mm diameter pipes. The cost savings for CI pipes are not as dramatic, but
nonethless beneficial, with a reduction to 60% of the repair costs for non-CP 150 mm diameter pipes and
a reduction to 70% of the repair costs for non-CP 300 mm diameter pipes.
Acknowledgements
The authors would like to thank the City of Toronto, particularly Robert Klimas and Abdul Syed, for
providing pipe break data. Thanks are also due to Jeanne Huang for assistance in the data manipulation
and to Krista Palen for assistance with data assembly. Funding was provided through the Joint
Infrastructure Interdependency Research Program and Canada Research Chair funds.
Received 13 February 2007. Revision accepted 4 July 2007. Published on the NRC Research Press Web
site at cjce.nrc.ca on 7 March 2008.
Written discussion of this article is welcomed and will be received by the Editor until 30 June 2008.
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List of Symbols
[J.sub.k] total number of pipes of material k, placed in the ground
k type of pipe material: k = 1 for CI pipes; k = 2 for DI pipes
n number of pipe breaks, within an individual pipe, since placement in the ground
L number of 5-year time intervals
[P.sub.k](t,n) probability that pipes of material type k break for the nth time
t number of periods since pipe placement in the ground (assumed for purposes herein that each period is
5 years in duration)
[X.sub.k,y](n) number of pipes of type k, broken for the nth time, up to and including within time period t
C. Schuster and E. McBean. (1) School of Engineering, University of Guelph, Guelph, ON N1G 2W1,
Canada.
(1) Corresponding author (e-mail: emcbeanC&uoguelph.ca).
(2) Shymko, R. The status of the cathodic protection program to minimize the effects of corrosion of
existing ductile iron water mains within the region of Durham. Report to the Region of Durham, Ontario,
January 2006.
(3) Klimas, R. City of Toronto, personal communication, 2006.
Table 1. Summary of pipe breaks in the Greater Toronto Area
(GTA) database.
No. of distri-
No. of pipes
No. of times
bution pipes
that have
pipes have
in inventory
broken
broken *
Scarborough
6519
3129 (48%)
12 635
Etobicoke
6566
3401 (52%)
11 946
East York
1584
506 (32%)
1 064
York
2340
438 (19%)
929
* Data only included up to the 10th break of an individual pipe and
post-1960.
Table 2. Average breaks per year and average time between breaks
pre- and post-application of cathodic protection (CP), for different
pipe material and soil types.
Average
breaks per year
Material and soil
type
Pre-CP
Post-CP
CI silt and clay
0.07
0.03
CI sand and gravel
0.10
0.00
DI silt and clay
0.06
0.01
DI sand and gravel
0.09
0.01
Average time
between breaks (years)
Material and soil
type
Pre-CP
Post-CP
CI silt and clay
3.86
4.79
CI sand and gravel
3.03
--
DI silt and clay
2.26
6.14
DI sand and gravel
1.98
7.50
Average
Average
Material and soil
year of
year of CP
type
construction
application
CI silt and clay
1965
1997
CI sand and gravel
1965
1997
DI silt and clay
1973
1997
DI sand and gravel
1974
1996
Note: CI, cast iron; DI, ductile iron.
Table 3. Probability of first break for pipe materials and soil
types post-application of cathodic protection (CP) for the cities
of Scarborough, Etobicoke, York, and East York.
Cast iron pipes
Next pipe
Sand-
Silt-clay
break in:
gravel
(%)
5 years
--
0.09
10 years
--
0.12
15 years
--
0.15
20 years
--
0.16
Ductile iron pipes
Next pipe
Sand-gravel
Silt-clay
break in:
(%)
(%)
5 years
0.07
0.06
10 years
0.08
0.07
15 years
0.08
0.08
20 years
0.08
0.08
Note: Data obtained from R. Klimas, City of Toronto, personal
communication, 2006.
Table 4. Overall probability of first break for pipes without
cathodic protection (CP), for different pipe material and soil type
for the City of Etobicoke.
Cast iron
pipes
Ductile
iron pipes
Next pipe
Sand-
Silt-clay
Sand-
Silt-clay
break in:
gravel (%)
(%)
gravel (%)
(%)
5 years
0.07
0.10
0.02 *
0.03 *
10 years
0.23
0.24
0.08
0.08
15 years
0.28
0.34
0.13
0.14
20 years
0.36
0.43
0.17
0.19
25 years
0.44
0.53
0.21
0.23
30 years
0.53
0.59
0.26
0.30
35 years
0.57
0.66
0.29
0.33
40 years
0.58
0.70
0.30
0.35
Note: Data obtained from R. Klimas, City of Toronto, personal
communication, 2006.
* For these two conditions, ductile iron pipes in sand-gravel and
silt/-clay, there is actually a lower probability of a pipe breaking
post-CP than pre-CP. These probabilities are likely the result of the
damage that occurred prior to CP placement.
Table 5. Annual costs associated with 100 ductile iron (DI) pipes, 10m
long and 150 or 300 mm in diameter, placed in silt and clay, with and
without cathodic protection (CP).
Average annual
Pipe
break rate per
Cost of CP
diameter (mm)
CP
100 pipes *
(CAN$)
150
No
6
N/A
150
Yes
1
300
No
6
N/A
300
Yes
1
100 000
50 000
Costs over
Pipe
Annual cost of
a 10-year
diameter (mm)
repair (CAN$)
period (CAN$)
150
30 000
300 000
150
15 000
100 000
300
30 000
300 000
300
15 000
150 000
Note: N/A, not applicable.
* Using average break rate per year for DI pipes in silt and clay
pre- and post-CP from Table 2.
Table 6. Annual costs associated with 100 cast iron (CI) pipes, 10 m
long and 150 and 300 mm in diameter, placed in silt and clay, with
and without cathodic protection (CP).
Average annual
Pipe
diameter (mm)
CP
break rate per
Cost of CP
100 pipes *
(CAN$)
150
No
7
N/A
150
Yes
3
300
No
7
N/A
300
Yes
3
100 000
50 000
Costs
Pipe
Annual cost of
over a 10-year
diameter (mm)
repair (CAN$)
period (CAN$)
150
35 000
350 000
150
15 000
200 000
300
35 000
350 000
300
15 000
250 000
Note: N/A, not applicable.
* Using average break rate per year for CI pipes in silt and
clay pre- and post-CP from Table 2.
Schuster, C.J.^McBean, E.A.
http://callisto.ggsr
en
Full Text: COPYRIGHT 2008 NRC Research Press.
http://www.nrc-cnrc.gc.ca/main_e.html
Source Citation:
McBean, E.A., and C.J. Schuster. "Impacts of cathodic protection on pipe break probabilities: a Toronto case
study." Canadian Journal of Civil Engineering 35.2 (2008): 210+. Gale Science In Context. Web. 4 Oct.
2011.
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Anti-corrosion systems gaining; the method
could save hundreds of thousands of bridges
The New York Times , June 8, 1988
GALE|A6398322
Anti-corrosion sy
The New York Tim June 8, 1988
¶¶¶¶¶
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Source Citation:
Sims, Calvin. "Anti-corrosion systems gaining; the method could save hundreds of thousands of bridges."
New York Times 8 June 1988: D8. Gale Science In Context. Web. 4 Oct. 2011.
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Gale Document Number: GALE|A6398322