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 Corrosion rate (inches penetration per year):
(0.704"-0.500")/4 = 0.051 ipy
51 mils/year (1 mil = .OOl inches)
Subsequent to thickness measurements, a detailed diver report and
photographs were made. The diver inspection included observations starting at
the surface and concluded at the mud line. Below water, the surface condition
changed and was observed to be covered by a soft powdery corrosion product
that was black in color. This film was easily removed to reveal the
underlying steel which seemed in good shape. This condition persisted all the
way to the mud line indicating uniform corrosion beneath the water. Although
no thickness measurements were made below water, the divers indicated the
piling appears to be sustaining leas damage below water than in the tidal zone.
Solution: The corrosion rate and damage to the pilings was unacceptable. Two
methods were recommended to control the corrosion rate:
The system providing the best protection was a near white blast of
a.
the steel followed by a 40 mil coat of carboglass 1601 polyester
glassflake manufactured by Carboline Company. Several other coating
systems performed well, but the glassflake received the highest evaluation
in the atmospheric, immersed, and sand-swept zones. The system also
provided excellent abrasion resistant and would hold up to the abrasion
produced by the camel mooring system used for the submarines. The problem
with using this system would be the cost of removing and reinstalling the
pilings. However, this would be protection recommended for any fender
pile system during initial construction or installation.
b.
A second method that would afford protection could be applied with
pilings in place. It is a system of epoxy encasement of the steel piling
in the tidal zone. A fiberglass form is placed around the piling and the
epoxy mortar is poured to seal out the corrosive environment. The firm
that provided this information is Logan Engineering Contracting Company in
Jacksonville, Florida. Since encasement of the piling all the way to the
mud line would be extremely expensive, catholic protection could be used
in conjunction with this system to yield acceptable results. However,
there is no documented corrosion performance data available on this
encasement system.
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