Thermal
Spray Metalizing - Applications
Journal
of Protective Coatings & Linings
November 1999
Dam
Metallized in Freezing Conditions To Beat Schedule
by Lori R. Huffman, Associate Editor
Beginning in mid-November 1998 and working almost
continuously through the end of May 1999, a contractor
endured frigid winter weather to abrasive blast
and metallize the St. Andrews Lock and Dam in
Lockport, Manitoba, Canada. The dam is the largest
of the world's three camera-type moveable dams,
which use wooden curtains that are lifted and
lowered on steel frames to regulate water levels.
("Camere" is the name of the river over
which this type of dam was first used.)
Tendered by the Public Works and Government Services
Canada (PWGSC) in the summer of 1998, the $8 million
contract specified that the 380,000,sq ft (35,300
sq m) of structural steel be solvent cleaned,
abrasive blasted, and metallized with 85/15 zinc
aluminum. The project's completion date was set
as March 31, 2000. In spite of work limitations
due to the operation of the lock and dam, the
contractor completed the project on June 23, 1999,
9 months ahead of schedule.
The
federal government has owned and operated the
camerestyle dam since its construction in 1910,
says John Davidson, senior project manager with
PWGSC. The structure was built to facilitate transportation
along the Red River by regulating water levels.
In 1913, a road deck was installed to link west
and east Lockport. A paper Davidson co-authored
about the metallizing project describes the structure
as follows.
"The
structure consists of six identical 38.6 m [127.4
ft] long river spans that house a 6-bay spillway
with a camera-type moveable dam, a lock, a seventh
38.6 m [127.4 ft} overland span adjacent to the
east approach, three cast approach spans totaling
73.0 m [24().9 ft] and an 89.9 m [296.7 ft] west
approach compromised of two spans. The six river
spans are made up of three trusses upper framing
members supporting the road above a working floor
providing access to the moveable dam, a main floor,
sway bracing and the moveable clam frames. The
main trusses are comprised of built-up lattice
box beams riveted together.
Channels, I-beams, and latticed built-up sections
were employed to make up the other components
of the structure. Below the working floor are
the moveable. tapered/ built-up, dam frame girders.
These are supported by an elaborate system consisting
of steel hangars, thrust wedges, and steel castings.
The seventh span is made up of two main trusses
identical to those supporting the road deck in
Spans 1-6. It also includes a crane storage facility
Figure 1 is a schematic of the lock and dam.
A thorough maintenance painting of the dam had
not occurred since the early 1970s. Most of the
existing coatings on the structure were composed
of lead-based alkyds. The condition of these coatings
varied, depending on the location of the coated
steel. Steel members directly under the road surface
were in fairly good condition, while the truss
and box beams closer to the water were failing,
says Jamie Turcotte, project coordinator for the
contractor.
Selecting the Coatings and Altering the Specification
The recently completed work was a continuation
of a $25 million rehabilitation project done by
PWGSC. In 1996, the owner hired Wardrop Engineering
to select the coating system and administer the
contract. Surface preparation and coating were
to take place on the six river spans, the dam
frames above the water line, and the single overland
span adjacent to the east approach.
The engineering firm conducted a cost-benefit
analysis of topcoated and untopcoated metallizing
versus over 70 combinations of high-performance
coating systems, including inorganic zinc/highbuild
epoxy/ poly-urethane, coal tar epoxy, moisture-
cured urethanes, and calcium sulfonate. The aim
of the analysis was to find the most cost-effective
system for a 50-year service life. According to
Robert van Ginkel, principal project manager for
the engineering firm that consulted on the job,
the cost-benefit analysis considered the location
of the substrate to be coated and the constraints
peculiar to the lock and dam. The analysis also
considered materials and labor costs, application
costs, containment requirements, overhead and
inspection costs, and winter work costs, as detailed
in Reference 1.
The study showed that although the initial cost
of metallizing was higher than that of traditional
coatings, the operation and maintenance costs
for metallizing were lower than costs for liquid-applied
coatings, says Davidson.
For the purposes of coating selection and cost-benefit
analysis, the firm divided the structure into
four corrosion zones. These zones were included
in the specification document to identify areas
that would be metallized or coated with a calcium
sulfonate coating. A calcium sulfonate coating
was originally specified on part of the structure
because PWGSC believed that metallizing the entire
structure would be cost prohibitive, says Davidson.
Making up Zone 1 was the submerged portion of
the retractable dam frames, which was deemed too
badly corroded to be rehabilitated and was instead
slated for replacement. Zone 2 included the above
water portion of the dam frames, three bridge
trusses 5.9 ft (1.8 m) above the bottom chord,
and the main and working floors of the structure.
This area, exposed to water spray from the dam,
was subject to corrosion and was to he metallized.
Zone 3 (the remainder of the 6 trusses) and Zone
4 (the floor beams and stringers under the road
deck) were to he coated with a calcium sulfonate
system.
Once the project was awarded to a prequalified
contractor, PWGSC issued a change order to specify
mctallizing for Zones 3 and 4. Davidson explains
that the contractor was as asked to submit two
bids for the work, one for metallizing some areas
and coating others with calcium sulfonate, and
the other for metallizing all areas. A lower than
expected metallizing bid coupled with the long-term
operations and maintenance savings offered by
metaliizing led PWGSC to metallize all areas.
Continued>
E-mail:
thermalspraying@plattbros.com
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