Corrosion Engineering Companion

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Annual cost of a paint system

1. Repaint every four years.

P

$5.12

{t(P-S)/n}(P/A, i%, n)

$1.87

-(1-t)(X)(P/F, i%, n)

-$2.11

n=4

-(1-t)(X)(P/F, i%, n)

-$1.55

n=8

S(P/F, i%, n)

0

PW

-$6.91

A

-$0.917 /m2

2. Biennial touch-ups instead of repaints every four years.

Biennial touch-up costs (X) at 2, 4, 6, 8, and 10 years can be expressed as an equivalent annual touch-up cost X with the following Equation:

X = X[(P/F, 8%, 2y) + (P/F, 8%, 4y) + (P/F, 8%, 6y) + (P/F, 8%, 8y) + (P/F, 8%, 10y)](A/P, 8%, 12 y)

(P/F, i%, n)

n

0.857

2

0.735

4

0.630

6

0.540

8

0.463

10

and X' = 0.4281 X

Repainting costs alone can be expressed similarly with the following formula:

A = -P[(P/F, 8%, 4y)+ (P/F, 8%, 8y)](A/P, 8%, 12 y)

or -$0.866 /m2

To be equal or less costly the annual equivalent annual cost of touch-ups should be equal or less that the repaint program, and hence:

0.4281 X = -$0.866 and X = -$2.024