Practical Welding Today - May/June 2009

As it embarks on its journey to California, a girder A fabricated by Stinger Welding is emblazoned with a message from the crew to the people of Oakland.

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-hydro-gen, 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 re-configuration 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.