May 2009 - In a single pass, a submerged-arc welding system lays down a 10-ft.-long bead to join two massive panels of steel. The segments are up to 90 ft. long, and after a series of them are brought together, they’ll produce an approximately 260-ft.-tall, 14-ft.-wide wind tower. To join sheets of steel that colossal and to construct a structure that immense, the welds have to be strong, and they have to be precise.

Although a wind tower’s 40-story height, from the base to the tip of a blade extended vertically, is impressive, the fabrication required is just as monumental when one considers how many wind towers are required to produce a substantial amount of electricity. They don’t typically work alone; they come in fields.

These wind tower generators are appearing everywhere from the Midwestern plains to the East and West Coasts of the United States. One company that builds the bases for these towers is Katana Summit LLC, Columbus, Neb., a joint venture between T Bailey Inc., Anacortes, Wash., a steel tank manufacturer, and Sumitomo Corp., Tokyo, a multinational Japanese corporation.

T Bailey is primarily a construction company specializing in large steel storage tanks. It was started by Darrell Lehmann and Gene Tanaka in 1991. The company manufactures and builds large steel storage tanks, drill shaft casings, large-diameter water pipes and wind towers.

The company’s first towers were built in 2001. "Then the wind towers took on a life of their own," says Lehmann, president. In 2005, he and Tanaka formed another company, Katana Industries. Then they were approached by Sumitomo Corp. of America, New York, which was looking to purchase a wind tower company.

"We sold them half of Katana Industries, and then the name changed to Katana Summit LLC," says Lehmann. "We broke ground in Columbus, Neb., in 2007 and went into production in 2008. It’s been a fast-track, and now we are doing more than $100 million a year in sales."

Generating wind
Complete wind tower packages are usually developed by the companies that provide the turbines, such as General Electric Co. or Mitsubishi Power Systems. They provide the turbine, the nacelle (which houses the turbine/generator system), the main support tubular structure and the blades. Katana Summit is a subcontractor, manufacturing towers to the specifications of GE, as well as other wind power providers.

These companies then sell the wind turbine system to a developer that buys the land, produces the application permits and sells it to the community to provide energy or to become the main electric grid. The business is primarily driven by private developers, says Lehmann.

"One of the support structures we’re working on now will provide 2 MW of power at about $1 million per MW," he says. "There’s really no such thing as a standard unit. They’re approaching large designs now where it becomes impractical to move them because transporting is the key to the size of wind towers."

Lehmann adds that if the tower becomes too large, special transportation permits are needed, which dramatically increase the cost of the unit. These costs play a large role in the size and style of the tower. Companies offer larger units like 5-MW turbines primarily for shoreline applications.

Construction
A wind tower turbine’s base is made of carbon steel. The base is constructed of tubes (or cans, as they are known in the industry) that don’t have any framework within the base because the thickness of steel offers the needed support. Inside the cans, steel supports are welded for things such as a ladder for service personnel, along with electrical lines or electrical parts.

Cans start out having a greater diameter on the bottom then narrowing toward the top. Steel for construction is normally high-strength, low-alloy with some A36 modified or 709 also used. All of it has stringent impact requirements, says Lehmann.

The thickness of the steel varies as to the requirements of the base. "It’s a calculation of diameter, height and load bearing," says Lehmann. "Larger-diameter tubes can use thinner steel, but smaller-diameter tubes need thicker steel. We just finished a tower for a company that’s 80 m high that had a small diameter base using a steel thickness of 48 mm. The steel base diameter is 13 ft., 10 in. The ones we are working on now have a 14-ft. diameter that tapers to 10 ft., using 22-mm-thick steel."

The nacelle, blades and turbine/generator weigh about 100 tons. Usually, a nacelle has a steel frame structure and a fiberglass casing around it. The blades are also made from fiberglass. Typically, the blades will be half the size of the tower height, generally 40 m long. The entire height of the wind tower is 80 m, plus another 40 m of blade height, which is normal for a 2-MW unit.

Lehmann says the company will buy about 100 sets of steel plate for 100 towers, which will take a few months to produce.

"When we start production, we’ll pull the plate for the various tubes according to our production schedule," he says. "If the tower section is made up of 10 cans, it means that one can at each end has a flange on it as an attaching area. Those will come on top of the pile, and we make sure they get to the flange station, so when everything hits the main production line, the timing sequence is in order.

"Our process starts with the production of single cans," he says. "The steel plates from the mill aren’t precut to exact size. We have to cut everything and bevel the edge for welding. Next, the steel is plasma cut, abraded to remove the scale, bent into a can and welded. Then the cans are built into the tower sections and welded together using a submerged MIG arc system provided by Amet Inc. [Rexburg, Idaho] with the welder power supplies from The Lincoln Electric Co. [Cleveland]. Welding is crucial, and every weld is inspected using ultrasound.

"After the tower section is built up, it goes to a clip-and-clean area, where all the welds are detailed, and the final inspection is completed. This is where the supports or the bosses are welded on for the ladders. They are then bolted together, as well as access platforms, power cabling or the turbine’s electric bus system. All welding is finished at this point. Now the finished base moves on to the blast and paint departments and then to final assembly, where all the internal parts are put in, such as platforms, cabling, lighting and ladders. From here, it leaves the building, covered and shipped to just about anywhere in the United States."

Tried and true
Although Lehmann says his companies have used different welding equipment manufacturers over the years, he always comes back to Lincoln Electric. "I’ve had good experiences with Lincoln Electric for more than 40 years of my life," he says. "It’s dependable, the service support is second to none and when you have technical issues, you get someone on the phone quickly. The company is aggressive on product development, and they don’t sell equipment before it’s fully developed. Lincoln also works with us for product development and use of consumables, such as getting the proper flux and wire combinations. We get good support from them."

Amet makes the controls and manipulators for the submerged arc welding system to weld the diameter seam of the cans.

"They’re closely tied to Lincoln," says Lehmann. "They’re good controls and manipulators integrated into a nice package."

Katana Summit uses Lincoln’s Power Wave AC/DC 1000 units to do all of its submerged arc welding. It’s a new technology that uses a balanced wave, which balances the DC positive and negative to improve control over the weld gap with high deposition, notes Lehmann.

"We use a twin-wire technology, where we have a lead arc and a trailing arc to get the proper weld," he says.

For hand-held MIG welding applications, the company uses Lincoln Electric’s M350, 380 and 400 welding systems.

"All of our welding operators are certified," says Lehmann. "We’re welding an average 10-ft. seam of 1.5-in. steel with the Lincoln equipment, averaging one every hour. We try to tailor our processes to using only one wire, one flux and one set of parameters. All of our welding is done to AWS D11 welding specifications. Along with getting a proper weld, overall weld appearance is important. We have three welding engineers who work hand in hand with Lincoln to develop the best welding practices."

Lehmann says wind tower manufacturers are offering many new designs to increase the output to up to 5 MW of power. He says 1.5 MW can light roughly 15,000 houses. But even with the many that are going up, wind-power generation satisfies only 0.5 percent of the total electric power demand in the United States. FFJ

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