Welding Update for Infrastruture:Building the bridge to anywhere
An Arizona-based bridge fabricator dares to be different, and succeeds
Stinger Welding Inc. has only been around for 12 years but quickly has established itself as a premier fabricator of bridges and bridge components in the southwestern U.S. Two years ago a projectinvolving an Oakland, Calif., bridge sent the company into thespotlight for its efforts in fabricating 12 girders in just eight days.
To say that Stinger Welding Inc. is unique could be considered an understatement. After all, the AISC-certified fabricator of bridges and bridge components from Coolidge, Ariz., prides itself as a team whose very livelihood is to fabricate, piece together, and erect components that hold human life in the balance. And given the projects the company has taken on—and the way in which they were carried out—who would be brave enough to dispute them?
Up and running since 1996, Stinger Welding has asserted itself as a fabricator to be reckoned with in the Southwest. Home to approximately 100 welders, the company—best known for its ability to complete projects quickly—has found success because of the quality of its work force and the commitment given by each individual, said Gary Gardner, quality assurance/quality control manager and CWI for Stinger.
"One of the things I really love about this place is we've got a very good work force," Gardner said.
"It starts with the people in production. If they're not completely committed to this, there's nothing that quality control can do to fix that. No matter how hard you inspect something, you're not going to turn something bad into something good. It has to come from the grass roots."
Working Fast, Maintaining Quality
Stinger's commitment to completing projects quickly does not mean the company sacrifices quality. Everything is built to quality requirements specified by codes and beyond, explained Gardner.
"We've got a very low defect rate coming out of this place."
Part of the reason that the quality of the welds has been so good, according to Gardner, is the processes the company leans heavily upon. The company chooses to use flux-cored arc welding, gas metal arc welding with metal-cored wire, stud welding, and submerged arc welding (SAW) for the larger pieces. In fact, it's not uncommon to see the welders using a SAW unit out in the field.
Typically, bridge fabrication and shielded metal arc welding (SMAW) go hand-in-hand. But at Stinger, SMAW is not the process of choice. Instead, FCAW makes up 80 to 90 percent of the welding done in the shop and on the job site.
"We'll take along a generator with constant voltage and a suitcase welding unit with wire feeder and gas bottles and crane those up wherever we need to weld. I've heard a few DOTs come by and say, 'We've never seen anybody do this before. You erect with flux-core?' Yes, we do. You can go up and X-ray it or ultrasonic test it and it will pass."
There are times when SMAW is the obvious choice, Gardner explained, such as in a tight spot where the welder can bend the electrode to reach around a corner. But for heavy structural applications in which the welds have to be really good, Gardner said SMAW doesn't make sense.
"It's very slow and it's more difficult to control your electrode. With FCAW we almost always get really high-quality welds with very little rework. We can sleep at night because we know we've put up something good."
In 2007 a gasoline tanker overturned on California Interstate 880, caught fire, and destroyed two spans of the overpass bridge on Interstate 580 near Oakland. The California Department of Transportation (Caltrans) immediately put the bridge reconstruction project out to bid for this span of highway—known locally as the MacArthur Maze—that handles in excess of 150,000 vehicles a day.
"The tanker accident had immediate and far-reaching effects on the local economy. Traffic had to be rerouted, other construction projects were delayed, and public transportation was terribly overloaded. Caltrans initially estimated it would take at least six months to complete the reconstruction," Gardner explained.
Stinger Welding won the subcontract for 12 plate girders, which would allow for emergency repairs to be made.
The company's experience in constructing fracture-critical bridge structures (projects that necessitate special certification due to the load-bearing configurations) helped it win the bid.
Stinger's steel buyer got on the phone immediately and found all the right grades of steel in about a half hour. Because this was a federally funded project, the steel had to be U.S.-made.
Once the steel was ordered, the company enlisted dual truck drivers to transport the material nonstop from the East Coast or the Southwest directly to Stinger's facility.
"Steel started coming in the day after we ordered it. It went right onto the burn table and we started cutting it into pieces," Gardner said.
Meeting both AWS and Caltrans stringent standards, the plate girders—or structural supports—for the MacArthur Maze were 42 in. tall, with the longest one measuring 90 ft. and the shortest about 60 ft. They are constructed from A709 Grade 50, a high-strength, low-alloy structural steel.
The majority of each plate girder fabricated on-site at Stinger's plant was done so using SAW. Stinger chose Lincoln Electric's Idealarc® DC-1000 power sources, LT-7 tractor wire feeders, NA-3 wire feeders, with Lincolnweld® LA-75 wire and 888™ flux.
The power sources were used in conjunction with three tractors and two feeders on manipulators to enable fabrication of these girders with SAW. Stinger found the combination of the wire and flux, along with the power source with the three tractors and the wire feeder, provided a number of advantages throughout the manufacturing process.
First, it satisfied the need for low-hydrogen, high-strength wire and flux, which is necessary for reliably welding the bridge's AASHTO M270/ASTM A709 Grade 50 steel in accordance with the AWS D1.5 code.
"The welds resulting from this combination consistently meet mechanical property requirements and provide extremely good low-temperature impact strength," Gardner said.
The wire electrode and flux combination is multipurpose, and Stinger was able to use the same consumable pairing for all its SAW applications, including the welding of weathering steel. This translated into time and cost savings as fewer procedure qualification records (PQRs) and welding procedure specifications (WPSs) were necessary.
The equipment also allowed for rapid reconfiguration for different welding processes, including FCAW, gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), and SMAW, as well as SAW, which decreased the amount of time Stinger spent on periodic calibration per AWS requirements.
Running two 10-hour shifts, the company was able to fabricate the 12 plate girders in just eight days, allowing the I-580 bridge spans to be reopened in just three months—six weeks ahead of best estimates. Caltrans initially estimated it would take at least six months to complete the reconstruction.
"Caltrans had six full-time inspectors on-site inspecting and nondestructively testing 10 percent of the welds, and they almost couldn't keep up with us. We had never seen a DOT move so fast," Gardner said.
In addition to its fast turnaround, Stinger's attention to detail translated into each of its 12 girders on the MacArthur Maze passing inspection without any required on-site rework.
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