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CATHODIC PROTECTION
Table
1 presents the results of a cost comparison study that shows the
economic benefit of employing cathodic protection in manholes.2
Even after replacing the anodes three times, the costs of cathodic
protection are only a small percentage of the costs of replacing
the entire pipe.
|
1
Kilometer
|
Replacement
Costs
|
Cathodic
Protection Costs
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Savings
|
Costs
of Cathodic Protection as a Percentage of Replacement Costs
|
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6
Inch Water Main
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$800,000
|
$20,000
X 3 cycles
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$740,000
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7.5%
|
|
12
Inch Water Main
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$1,100,000
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$37,500
X 3 cycles
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$978,500
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10.25%
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Table
1: Comparison of the Cost of Replacement and Cathodic Protection
of One Kilometer of Water Mains in Ottawa-Carleton, Ontario Canada
VALVE CASE STUDY CONCLUSIONS
The
case studies showed the significance of quality and cost of protective
coatings, but, more importantly, they showed the overall quality
that could be achieved by the use of some high quality coating materials.
With the valve chamber protected with a wax coating 40 to 50 years
of protection can be expected.
Monitoring
of chambers is still essential in the maintenance process. In light
of the potential for the stainless steel to fail as a result of
crevice corrosion, close monitoring is required of the valve chambers
even where stainless steel bolts have been installed. Each valve
chamber will act differently in the corrosion cycle as the conductivity
of the soil surrounding the chamber and, by default, the water entering
the chamber is different. Again, each chamber will maintain infiltration
and retain the water at a different rate thus affecting the corrosion
rate.
These
test sites will be monitored on a regular maintenance schedule as
well as spot checks on some of the areas of a more critical nature.
This will be a long process in the total assessment of the valves,
both chambered and direct buried.
Careful
progress will be required to understand all the possible types of
corrosion that can affect the system. The most important part of
this process is to gain the support of the staff on the necessary
changes. The norm is always, "if it ain't broke don't fix it." Staff
will perform a detailed review of each valve chamber and assess
the valve condition and make the necessary changes, so that the
correct field decisions are made. This decision-making matrix will
only arrive through training and understanding of the application
of corrosion control.
ACKNOWLEDGEMENTS
A special thanks to Winston Revie and Tim Biere for their
support and encouragement in preparing this paper.
REFERENCES
-
J.T.N. Atkinson and H. Van Droffelaar, Corrosion and
Its Control, An Introduction to the Subject, 2 nd Edition, NACE
Intermational Houston, 1995 Page 270, 280, 281, 281.
-
D. Raymond, "Cathodic Protection of Water Infrastructure
in Cold Climate-Experience in the Region of Ottawa-Carleton,
Ontario, Canada," Paper 01310, Corrosion 2001, NACE, Houston,
2001.
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