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TEAM
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Water
Tank Coating Selection Not
long ago the hardest decision for
the water tank owner to make in coating or recoating his
water storage tank was the selection of the finish color. Both interior
and exterior were prime coated with a red lead primer. The standard interior
finish coatings were a phenolic or bitumastic. If a "long life" exotic
system was desired, a "hot applied coal tar enamel" was used. If a
short life, inexpensive system was desired, the interior was quickly coated with
a "grease wax" coating. In fact, some of these coatings were applied
while the painter floated in a raft as water was drained from the tank. The
exterior was generally topcoated
with two coats of a leafing alkyd
aluminum. That
was yesterday. Today, coating selection for the water tank literally requires a
specialist. Coatings must comply with environmental regulations and yield
acceptable service life. There are so many requirements today that even we who
specialize in this field must constantly keep updating our knowledge of the
industry. This is normally done by attending refresher classes, seminars
participating in professional trade associations such as the Steel
Structures Painting Council (SSPC) and NACE International (NACE) and continually
upgrading our knowledge of OSHA, EPA , State and
Local governing agency requirements. Some
of the issues facing tank owners considering painting or repainting are:
*Open air abrasive blasting.
*VOC Compliant coatings
*Existing Lead based coatings
*OSHA Rules for workmen.
*Hazardous material/waste handling and disposal.
*Health Board approval of potable tank linings. Many
questions must be answered before
making the coating selection, among them are: :
*Is the tank structurally sound?
*What is the condition and type of existing coating?
*Do the existing coating systems contain lead?
*Can the existing coating be touched up?
*Does the existing interior coating meet Health Board
requirements?
*What about environmental conditions?
*What are the environmental concerns? The
first question that must be answered before selecting a coating system is to
determine if the existing coating
contains lead based paint and to determine what effect this lead based paint
will have on the recoating process. Prior
to 1977 most paint systems were
based on red lead primers. This one
time work horse of the coating industry, now
classified as "hazardous material", creates one of the greatest
problems in repainting structures. If
the interior coating of a potable water storage tank contains lead, the problem
cannot be ignored. This coating
must be removed and the surfaces re-coated with a material that is approved for
potable water use. If exterior
coatings contain lead based paints, alternate solutions to complete
removal may be available. If
complete removal is required, the lead must be contained, the workmen
protected, and removed paint and spent abrasive disposed of in an
acceptable manner. It
is not surprising to see the cost of a re-paint job be more than the cost of a
similar size new tank. A recent low bid to re-paint a 100,000 gallon, lead
based, elevated water tank was $269,000.00. The current value of that tank,
brand new today, would be about $175,000.00 complete with foundations and
painted. That owner decided to let
that tank "rust" away. In
the last 15 years, the costs for a re-paint job have increased by as much as 80%
for non lead based paints and can be as much as 700%
for lead based projects that may have hazardous waste removal.
The
cost to field paint
new tanks has also increased significantly over the past 15 years. These
costs have risen from about 5% of the total tank cost to more than 15%.
What
is a tank owner to do? Select
a competent, experienced engineering firm to perform the following: A.
An evaluation to determine the structural condition of the tank and what
repairs and renovations are necessary and their estimated cost. B.
Tests of the existing coatings including:
1.
Adhesion tests.
2.
Thickness tests.
3.
Lead tests. C.
Prepare an engineering report that describes the present condition of the
tank and it's coating. This report should address estimated costs for performing
repairs and renovations and recoating costs. Options should be presented that
outline a Value/Engineering approach to assist the owner in selecting a cost
effective solution within available budget
constraints. D.
Prepare a comprehensive, detailed specification
that will yield a maximum benefit contract at a minimum cost. E.
Provide a competent inspection
program administered by trained professionals that will assure the project is
achieved to the specification and will achieve the desired life expectancy. The
days of grabbing a bucket of primer and a pail of finish paint to start painting
the city's water tank are over. Today's
coatings are sophisticated, designed materials that are designed to yield low
maintenance long life cycles if properly applied. The key to achieving the
manufacturers performance expectations is "proper application".
It is estimated that 85% of coating failure are attributable to improper
application of the coating. |
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