Golden Gate Bridge Maintenance Is More Productive with NLB
WIXOM, MICH – A switch from sandblasting to high-pressure water jetting has reduced maintenance time for floor beams on the Golden Gate Bridge by some 60 percent, while minimizing flash rusting on the landmark structure.
Constant exposure of the bridge's metal surfaces to salt air produces rust that penetrates the metal and leads to distortion. Although the rust is regularly sandblasted, using needle guns and hammering to remove the heaviest build-up, some rust is always left behind, painted over and left until the next inspection. So the Golden Gate Bridge Highway and Transportation District is now using ultra-high pressure (UHP) water jetting equipment from NLB Corp. on the floor beams.
Rotating water jets at pressures up to 40,000 psi penetrate deeply between the rust and metal, removing rust and old coatings more productively than sandblasting without damaging the surface. A stress plate that previously required an entire shift to clean is cleaned to the SSPC WJ-2 standard in just 30 minutes by an operator with a lightweight NLB NCG8450A-3 rotating lance. The surface is then dried with compressed air so that a moisture-cured primer can be applied the same day, reducing the chances of flash rust.
After the primer, repairs are made and fasteners replaced as needed, followed by the application of a moisture-cured urethane coating (three coats). Completing this entire process on a single beam took four weeks when sand blasting was used, but with water jetting four beams can be completed in six weeks.
The UHP water is provided by an NLB 40125D pump unit, a diesel-powered unit that is convertible in about 20 minutes to any of eight pressures, from 6,000 psi to 40,000 psi (415 bar to 2,800 bar). The NLB 40125D has a 125 hp engine and delivers flow of up to 4.4 gallons per minute (16.5 lpm). Due to the limited space on the bridge, NLB made changes in the unit's standard configuration and manufactured a custom skid that would fit on a side path. The custom skid evenly distributes the weight of the pump unit, including its water and fuel.
In addition to improving surface preparation productivity, the Golden Gate Bridge Highway and Transportation District has found that water jetting simplifies containment and disposal. Keeping sand from falling into the bay during sandblasting, or onto the heavily-traveled bridge, was a major challenge, with pounds of sand and rust piling up on the scaffold to be shoveled into buckets and lifted to the deck.
Water jetting generates much less less debris, which is contained by a filter fabric installed over the floor. The water drains to trailer-mounted tanks below and taken away for treatment. Water jetting also generates no dust, eliminating the need for ventilation.
NLB's role in the project went beyond manufacturing the equipment. The company provided technicians to set up the pump unit on the bridge, conducted operator training and safety training and spent two days on-site trouble-shooting.
About NLB:
NLB Corp. (www.nlbcorp.com), a global leader in high-pressure and ultra-high pressure water jet systems, manufactures a full line of quality water jetting pump units and accessories for contractor and industrial uses. Applications include drill pipe cleaning, tube and pipe cleaning, product removal, surface preparation, pavement marking and rubber removal, tank cleaning, tube bundle cleaning, concrete hydrodemolition, concrete and pipe cutting, and more.
The NLB pump unit was specially configured to fit the Golden Gate Bridge.
Contact:
Jim Van Dam
Phone: 248-624-5555
Fax: 248-624-0908
e-mail: jim.vandam@nlbusa.com
