Thermal
Spray Metalizing - Applications
Journal
of Protective Coatings & Linings
November 1999
Dam
Metallized in Freezing Conditions To Beat Schedule
(continued)
by Lori R. Huffman, Associate Editor
Job Holds Many Challenges
Working around the operation requirements of the
clam was one of the chief challenges for the contractor.
With the prospect of interrupted work and nearly
complete demobilization demands, the contractor
decided instead to work through the winter months
when the dam was out of service. Because operations
would lace interruption again in the middle of
May when the dam resumed operations and because
of the expense involved in heating containments
for two winters, the contractor launched an aggressive
work schedule to complete the whole project in
one winter and spring, says Turcotte.
Riveted, built-up box beams and lattice work would
make access with abrasive blasting and metallizing
equipment difficult, he adds. The project's location
in an environmentally sensitive area and the presence
of lead-based paint on the structure added another
challenge to the job-total containment of the
operation. The structure is situated over a nautical
waterway popular for sport fishing and tourism.
Previous work clone to the lock and dam over the
last 10 years had already generated environmental
lawsuits, so the present contract was clear on
the need to contain all particulate from the blasting
operation, notes Turcotte.
Project Demands Influence Equipment Selection
The project would require application equipment
to be run almost continuously, yield high production
rates, and be handled easily. The contractor evaluated
metallizing equipment from six manufacturers.
After narrowing its choice to two candidates,
the contractor invited both manufacturers to demonstrate
their equipment. The contractor based its decision
on the deposition rates determined at the demonstration,
the ability of the equipment to spray-, 3/16-inch
(4.8 mm) 85/15 zinc aluminum wire, the size and
weight of the equipment, and the weight of the
gun and leads. Ultimately, the contractor purchased
7 units for the project, says Turcotte.
Double-Walled Containment
Keeps Particulate in, Weather Out A double-walled
containment designed for the project served two
purposes: protecting the environment and providing
a work area sheltered from ambient conditions
almost always below freezing, says Turcotte. The
containment measured 140 ft (42 m) long by 50
ft (15 m) wide, by 30 ft (9 m) high, allowing
an entire span to be enclosed. The exterior was
composed of a proprietary enclosure system constructed
of extruded aluminum m with " C " channels.
Insulated tarps with welt hems were anchored through
the channels. Separated from the exterior by a
two-foot cavity, the interior wall was made of
plastic shrink wrap and attached to steel scaffolding
with plywood flooring.
The contractor used three containments during
the operation: one for abrasive blasting; another
for metallizing; and a third for the next area
to be worked on. To allow workers a fast transition
from one area to the next, the third containment
was set up while the other two were in use, says
Turcotte (Fig. 2).
Inside the containment, the contractor maintained
air movement with three dust collectors (with
60,000 cfm t1,800 cmmi, 45,000 cfm f1,350 cmm],
and 30,000 cfm t900 cmm] output). Spent abrasive
was removed by a vacuum truck and automatic offloader,
says Turcotte. Within the metallizing enclosure,
gas heaters maintained temperatures above freezing
on milder days and just below freezing on days
when the ambient temperature was -22 F (-30 C).
Gas heaters were also used in the abrasive blasting
containment to maintain conditions and an environment
comfortable for the blasters, he says.
Blasting and Metallizing the Steel
The contractor's crews operated two, ten-hour
shifts seven days a week to complete the abrasive
blasting and metallizing, says Turcotte. Twelve
workers on the night shift handled the preliminary
abrasive blasting. Because of the difficulty of
achieving bright lighting at night, another four
to six workers performed the touchup blasting
during the day, he says. Seven metallizers also
worked during the day.
The specification required solvent washing (SSPC-SP
1 ) to remove chloride and oil contamination from
the steel, then blasting to an SSPCSP 10 (Near-White
Metal) finish with a two- to three-mil (50- to
75-micrometer) profile. Areas of pack rust in
joints were to be abrasive blasted to a depth
equal to or greater than the width of the joint,
metallized, then sealed with an elastomeric caulk,
says Turcotte. In the humid areas above the dam
gates, steel connections were to be metallized,
then stripe coated with a urethane mastic.
The contractor used coal slag for blasting. Spent
abrasive, paint debris, and dust from the dust
collectors were tested for hazardous content at
an independent laboratory.
According to Turcotte, hazardous waste was transported
to a licensed waste disposal site. Waste classified
as non-hazardous was disposed of in a certified
landfill licensed for solid industrial non-hazardous
waste.
Following approval of the surface preparation
by all inspectors, the contractor applied the
85/15 zinc aluminum metallizing by arc spray equipment.
The specification called for a minimum 1 0-mil
( 2 5 0-micrometer) thick coating; the dry film
thickness of the metallizing averaged 1213 mils
(300-325 micrometers), owing to the actual surface
profile of the steel, which measured 3 to 4 mils
(75 to 100 micrometers), says Turcotte.
The greater profile was attributed to the contractor's
use of blast pressures of 110 to 120 psi (758
to 827 kPa) to remove tightly adherent pack rust
from the steel. Because metallizing relies on
its mechanical bond for adhesion, says van Ginkel,
the deeper profile was beneficial. Also, the profile
required the deposition of a thicker coat of metallizing,
thus increasing the amount of zinc available for
cathodic protection.
The specification required a minimum adhesion
value of 700 psi (48 MPa) for the metallizing
when application took place with steel in air
temperatures of less than 39.2 F (4 C). Measured
adhesion values ranged from 700 to 1,100 psi (48
to 76 MPa). Adhesion was checked on an hourly/daily
basis using pull-off adhesion testers. Thickness
measurements were taken using coating thickness
and tooke gauges.
Considerations for Safety, Health, and
the Environment
The contractor followed an extensive worker protection
program, producing a job-specific safety manual
for the work and keeping a safety manager on staff.
In addition to its regular training, the contractor
held three, one-day worker training sessions on
lead, general health and safety, confined spaces,
and traffic control, says Turcotte. It also conducted
a pre-job safety hazard analysis and formed an
on-site safety committee, he says.
The contractor provided workers with decontamination
and shower facilities, protective clothing, and
respiratory protection. Supplied air respirators
were used during blasting and blow down, positive-flow
filtered air respirators were used in transit
to the work area within the containment, and HEPA-filtered
half mask respirators were used at all other times.
The contractor also implemented a medical surveillance
program, which included on-site audiometric testing
and blood lead level testing, says Turcotte.
In addition to the use of the double-walled containment,
a program of testing and monitoring of occupational
and ambient air, soil, wastewater, dust deposition,
blasting waste, and filter dust was undertaken.
In addition, breathing air samples were collected
and analyzed.
The contractor provided a site specific safety
plan, environmental compliance plan, and hazardous
waste disposal plan in addition to its general
safety policy and lead abatement program.
Layers of Inspections
Inspection of the surface preparation and metallizing
was of primary importance on this project, owing
to the unforgiving nature of metallizing, says
van Ginkel. According to Turcotte, the project
encompassed four layers of inspection. First,
the blasters on the job would review their work,
followed by the contractor's job inspector. Then
the contractor's NACE Level III inspector would
sign off on the work. Finally, the Public Works'
third party inspector, also certified by NACE,
would approve or disapprove of the completed work.
According to Francis Burke, president of the inspection
company hired by the owner, if areas did not conform
to the specifications, the inspector would inform
the contractor's inspector and have the abrasive
blasters or metallizing applicators return and
rectify the problems.
Davidson notes because of the complexity of the
structure, the contractor had to go over some
areas a number of times to remove the original
mill scale and make sure the areas behind rivets
were adequately prepared. Metallizing the steel
was also tricky, says Burke, because areas could
be easily missed owing to the similar appearance
of bare blasted steel and metallizing.
According to Burke, the contractor did a good
job. "When problems were brought to their
attention, they cleared them up quickly. The contractor
was dedicated to doing the job well and on time,"
he says.
Five-Year Warranty with a Twist
As stipulated by the contract, the contractor
provided a five-year, single-source warranty on
the metallizing. The unique aspect of the warranty,
according to van Ginkel, is that the contractor
was required to give the owner $300,000, to be
held in reserve during the warranty period. After
completing three-, four-, and five-year inspections
and any necessary repairs to the metallizing,
the contractor will be given $100,000 and the
interest accrued on the $300,000 after the five-year
inspection, says van Ginkel.
Less than 5% of the total contract, the warranty
money is enough to ensure a good job, but not
so much as to increase the tender price of the
contract or place a financial burden on the contractor,
van Ginkel notes.
The engineering firm will be responsible for providing
follow-up inspections on the dam and bridge as
part of the warranty provisions, he says.
Following up the Project
"The job] restored my faith in project coordination,"
says Davidson. "The project went very well,
and everyone involved worked as a team to accomplish
a complicated task in a short amount of time."
The project was conducted when the dam frames
were raised. When lowered, the PWGSC found that
some areas had been missed, says Davidson. The
contractor returned to the site in September for
touch-up metallizing, says Turcotte.
Clara Industrial Services Ltd. (Thunder Bay, Ontario)
managed the project and prepared and metallized
the structural steel. Wardrop Engineering (Winnipeg,
Manitoba) performed the cost-benefit analysis,
coating selection, and contract administration.
To-Spec (Ottawa, Ontario) performed inspections
for the owner. Mulder's Inspection Services (Hamilton,
Ontario) performed inspections for the contractor.
The exterior containment was made by Walton Technology,
Inc. (Richardson, TX). Scaffold Connection (Edmonton,
Alberta) installed the containment and manufactured
the shrink wrap elastic. Thermion Metallizing
Systems, Ltd. (Silverdale, WA) manufactures the
metallizing equipment. Caroline (St. Louis, MO)
supplied the urethane mastic coating.
Reference
1. John Davidson, David Bowen, Kristina Hunter,
and Robert van Ginkel, 'Fortifying the St. Andrews
Lock and Dam Zinc Arc Spray Metallizing,"
presented at The March 99 Workshop, sponsored
by Wardrop Engineering, March 23, 1999, Winnipeg,
Manitoba.
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