Welding Preheat Time Reduced in Lambeau Field Structural Steel Project

Steel reinforcements call for weld preheating

Miron Construction began work on reinforcing existing steel structures at Lambeau Field in September 2011. To support the structures for the new video board and the new seating in the south end zone, Miron added an additional bay to the existing bowl and built seven new levels on top of the existing three levels. It required major reinforcement of the existing steel columns.

This reinforcement included extending base plates and adding plating and bar stock to the existing columns. They also added large 3-inch plate steel caps to the top of each column to act as a base for the new steel structure. In order to do this and meet structural requirements, they had to bring the new plate steel as well as the existing column (16 inches by 16 inches) to a temperature of 150 degrees Fahrenheit — and maintain that temperature during the welding process.

Preheating in welding helps prevent rapid cooling of the weld metal, relieves stresses and drives out hydrogen, which can lead to cracking and embrittlement. In the construction industry, contractors typically use use propane-fueled torches (aka rosebuds, weed burners, etc.) to preheat steel for welding. This method of heating, however, poses problems, including:

• Inconsistent heating throughout the steel. The large size of the columns combined with the cold weather when Miron performed much of this work made it difficult to evenly maintain temperature.
• Purchasing, storage and handling of volatile heating fuel.
• Safety dangers associated with using a high-temperature open flame.
• Constant starts and stops during the welding process to bring the column back up to temperature using a heating torch.

A different solution

With the ProHeat™ 35 induction heating system from Miller, Miron Construction was able to bring each column or cap plate to temperature, leave the induction heating coils in place, and make the complete weld without stopping (except to switch out stick electrodes). This saved a substantial amount of time and provided uniform heating throughout the weld area.

“The induction heating system has actually been great for plating the columns and welding on the side,” explains Jake Wirkuty, an ironworker with Miron Construction. “It saves a lot of time on the preheat setup. Instead of welding 3 inches, preheating and then welding 3 inches, it’s been excellent just to slap the coil on the side of the column. We have an 8-foot setup, which, with two guys, one on each side of the column welding and keeping that temp up, it saves probably half the time or more of preheating.”

Benefits of induction heating

An induction heating system creates heat electromagnetically in the material rather than by surface heating, as with an open flame. Heat is induced by placing the steel in an alternating magnetic field created by liquid-cooled induction heating cables. In this application, Miron Construction rigged an 8-foot-long strip of plywood with the induction heating cables so it could be quickly and easily placed along each 2 1/2-inch thick reinforcement plate. The induction cables do not heat up themselves, but create eddy currents that generate heat throughout the plate and column. Two welders then worked down the side of each column plate.

“What we ended up doing with the coils for the unit was taking an 8-foot sheet of plywood, cutting it down to the size of our column plate, and zip-tying our coils to it and clamping the plywood to the edge of the column,” says Wirkuty. “When that side is done and heated, you just unclamp it and move to the other side. It makes it very easy to get around.”

The process is safer, faster and easier to use than other heating methods and typically provides more uniform heating throughout the part. The part comes to temperature within minutes and is kept at that temperature until the welding process is completed and the system is turned off or ramped down. Unlike heating with a torch, where the uniformity of heat is at the mercy of a number of factors — including ambient temperature, operator technique and the size of the column — induction heating heats the piece evenly throughout. Since they completed much of the work in winter in northern Wisconsin, the ability to reach and maintain that temperature was important.

“It’s been very important to have an even heating system,” says Wirkuty. “That way our welds, if you’re welding on the plate and trying to heat the column at the same time, with a weed burner or torch it seems like it’s very hard to keep that heat consistent. With this heat induction unit, that heat flows right through the plate evenly and it heats the column evenly.”

Safer, versatile option

In addition to uniform heating throughout, induction heating also creates its heat without an exposed heating element, making it considerably safer than using a propane torch. There is no open flame to burn anyone or catch anything on fire, and the coils remain cool to the touch even during the heating process. It also reduces the need to handle potentially volatile heating gases, which improves overall safety and helps lower that consumable cost.

“It will be a lot easier because you don’t have to switch out the fuel so often,” says Wirkuty. “And storing them you have to set up your own site and cages with the right signage and everything else. This system, you can just roll in. You don’t have to worry about any of that.”

The unit plugs into most standard 480-volt three-phase receptacles found onsite or on generators, making it extremely versatile no matter the type of jobsite.

“Being electric, just hooking it up into the building, you don’t have to run a giant generator,” says Wirkuty. “You can just hook it up and go.”

Improve preheating quality, safety and efficiency

While quality and safety are paramount, productivity is also an obvious factor. With this being a high-profile project with strict deadlines to meet, any process that increases productivity is going to be given serious consideration.

Induction heating allows welders to bring the part to temperature in less than half the time of heating with a torch and eliminates the need to stop welding to reheat the part — reducing total welding cycle times. When factoring in all of the benefits, Wirkuty knows it’s a viable and much more efficient technology for this application that will help lower total weld cycle costs.

“I think over the long run, the machine would actually pay for itself between the cost of acetylene and oxygen or propane heating it,” says Wirkuty. “And the productivity of it jumps way up.”

Reader’s note: This is the fourth in a series of articles detailing the expansion of Lambeau Field in Green Bay, Wisconsin, home to the Green Bay Packers of the National Football League. Miller Electric Mfg. LLC and Hobart were named the Official Welding Equipment Provider for the Lambeau Field Expansion by the Green Bay Packers. Through a partnership with Miron Construction Co., Inc. — the Official Provider of Construction Services for the Green Bay Packers and Lambeau Field — Miller and Hobart worked to bring the latest welding technology to the site.