Selecting an Engine-Driven Welder for Structural Steel | MillerWelds

Selecting an Engine-Driven Welder for Structural Steel

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Whether stick or flux cored welding, there are many variables to consider when selecting a welder for structural steel applications.
Welder stick welding with Miller equipment

Held together by thousands of pounds of weld metal, today’s structural steel buildings are built under the guidelines of AWS codes D1.1-D1.9. These codes dictate specific welding processes and techniques for everything from moment frames to floor deck and handrails. But there are other variables to consider when selecting a welder generator for structural applications.

What is the best engine-driven welder for structural steel welding?

The two most common processes in structural welding are stick and flux cored. Both are self-shielded and offer less chance of contamination compared to a solid wire with a shielding gas (wind blows away the shielding gas in outdoor applications). Stick has the simplest equipment, the lowest cost, and is relatively easy to use. Flux cored is advantageous in high volume applications as it is more efficient and has higher deposition rates. The wire feeder requires a constant current (CC) or constant voltage (CV) welder. A CV welder is required with wires designed to meet specific codes/requirements, such as AWS D1.8. Such wires are not designed to run with a CC welder.

Most contractors choose a machine that performs stick, flux cored, MIG, TIG, carbon arc gouging, and are even compatible with spool guns for MIG welding aluminum (for use on handrails and other internal/finishing components). Machines ranging from 250-300 amps provide more than enough power to meet the demands of most structural electrode diameters and codes.

“We need a 300-amp machine to run the 5/64-in. wire that gets us to production speeds and allows us to be competitive,” says Kevin Callahan, project manager, Apex Steel. “A 200-amp machine isn’t going to do it.”

Power generation capabilities

Engine drives offer power generation capabilities ranging from 5,000 to 20,000 watts. Choosing the right one depends on the tools you run and if you need to simultaneously weld and run other tools. Knowing the wattage needed to run tools such as grinders (1,800 watts), cut-off saws (up to 2,400 watts) and air compressors (8,200 starting watts) will help you pick the right unit.

"When you only have to move a single unit from job to job, you have obvious cost savings in labor and fuel," says Steve Price, president, Coastal Steel (Tacoma, Wash.). "The less you have on site, the less cluttered things are, and the less equipment you have to secure at night to prevent theft. Having this one unit makes obsolete the other individual pieces of equipment. And it doesn't take any more fuel to run than just a stand-alone welder.”

Another factor to consider is whether it has enough generator power to sustain both a welding arc and power tools. Some models feature independent welding and auxiliary power, while others offer enough auxiliary power so interference is not a concern. Interference with the welding arc leads to reduced penetration, an unacceptable compromise in structural steel welding.

“If you’ve got a guy welding, and another crafter comes along and plugs in a vacuum, it will mess with his arc,” says Calahan. “It’s an advantage not having to worry about that."

Air capabilities

Manufacturers now build air compressors into engine-driven welders to create a powerful three-in-one tool. These are especially useful to structural steel welders: contractors can now weld, and run power and air tools simultaneously off one central unit. (See Miller's Trailblazer 302 Air Pak).

“We'll pull a 12/3 power cord off its auxiliary power to run the shear wrench," explains Chad Hummel, field superintendent, Coastal Steel. "And while one guy is doing that, you can run a pneumatic button punch and weld at the same time. All of that can go on if you have a unit centrally-located and enough air hose and welding lead to reach."

"There's no longer a need for a compressor and a welder,” says Price, “thereby saving the cost of transporting two machines and the fuel to run those two machines. It uses virtually the same fuel while both operations (compressor and welder) are working.”


What type of fuel do you need? The most popular engine drives are available in gasoline, diesel and even LP. Gas engines offer a lower product cost, reduced weight and a smaller size. Diesel engines use 20 to 35 percent less fuel, have longer engine lives and are required on some sites. New electronic fuel injected (EFI) gas engine-driven welders further reduce fuel use by as much as 27 percent—a major benefit as many contractors are prohibited from storing fuel on site.

“It’s not just the price of the fuel,” says Callahan. “It’s the time it takes to get it — it’s a killer. It could easily be an hour for my superintendent to take the cans and go to the gas station and fill them up. If we can improve the fuel economy of our machines, the less time we’ll spend filling them up. It’s a huge time savings.”

Equipment for structural steel welding

Consider portability before you choose a machine—are you working on a single-story building or a ten-story high rise? Will a machine on a trailer or running gear suffice, or are lifting points needed for a crane/hoist? Noise consideration may also be a concern depending on where you work. Generally, keep machines simple. Structural welding is straightforward—bells and whistles may over-complicate the process.