MIL-HDBK-1004/10
have a thorough knowledge of corrosion control and to implement the best
strategy. The six-step economic process facilitates this goal. The following
examples illustrate this process.
13.4
Economic Analysis - Example 1
13.4.1
Objective.
Install a water pipeline, 4 inches in diameter and
10,000 feet long.
13.4.2
Alternatives
a)
Steel line without cathodic protection
b)
Steel line with cathodic protection
c)
Plastic line
This list is not exhaustive. All feasible alternatives should be examined
that will meet the objective. For clarity of demonstration, only three
alternatives will be considered in this example.
13.4.3
Assumptions
a) The soil resistivity is equal to 5,000 ohm-cm, pH 6, which is a
moderately aggressive corrosion environment.
b) The economic life of a water pipeline is 25 years. It is
assumed that no salvage value will be remitted in year 25 unless total
replacement is cost justified at that point in time.
c) The predicted number of leaks due to corrosion failures on the
steel line without cathodic protection increases exponentially after the first
leak in year 15. This prediction is based on historical data and technical
expertise.
d) The predicted number of leaks on the steel line with cathodic
protection is zero. Continued maintenance and protection is assumed. A major
rehabilitation of the system is required every 15 years. This prediction is
based on historical data and technical expertise.
e) The predicted number of repairs due to mechanical damage on the
plastic line is two per year. This prediction is based on historical data and
technical expertise.
f)
To compute present values, a 10 percent rate is assumed.
g)
This analysis requires no special treatment of inflation.
13.4.4
Cost/Benefit Analysis
13.4.4.1
Cost - Alternative 1--Steel Line Without Cathodic Protection. Cost
of steel line without cathodic protection - 0,000. Cost to repair leaks -
@ ,000 each.
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