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Welding

Tack-welding integration pays off

By David G. Kilburn

Adding Lincoln Electric’s Power Wave AC/DC 1000 SD allowed United Spiral Pipe to nearly double line speed, while boosting quality

December 2013 - Each day, fabrication crews at Pittsburg, Calif.-based United Spiral Pipe LLC are charged with one task: producing high-quality, large-diameter, helical-submerged-arc-welded spiral pipe for the oil and gas industry. And they do just that—at record-breaking speeds.

The pipe mill is a joint-venture between U.S. Steel, SeAH and POSCO and uses an advanced automated two-step welding process capable of producing 300,000 net tons of line pipe per year. Outside diameters of produced spiral pipe range from 24 in. to 64 in., using A252- through X80-grade steel with wall thicknesses from 1⁄4 in. to 1 in. The process consists of one forming and three welding lines.

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Two-stepping through production

Two-step spiral SAWH-pipe fabrication begins with forming, tack welding and cutting. Hot-band coils unwind on a mandrel and feed into an edge miller that cuts and prepares strip edges for the tack welding process. The feed angle depends on strip width and final outside diameter. From there, the pipe is formed into the proper diameter and tack welded via a large-wire GMAW process and cut in lengths from 40 ft. to 80 ft.

The second step sends the tack-welded pipe into one of three final welding stations. There the pipe’s tack-welded seam is rewelded using SAWH to meet API 5L standards and customer requirements.

The tack weld is vitally important, especially in applications such as spiral-pipe production where consistency and quality are a major influence in welding speeds at later stations. Reduced spatter brings that consistency and quality at United Spiral Pipe, allowing for faster downstream speeds and the near elimination of tack-weld repairs.

Welding speed nearly doubled  

Upfront during initial tack welding is where the mill has gained true speed and efficiency with measurable quality improvements. Welding speeds have nearly doubled at the tacking station by deploying the PowerWave AC/DC 1000 SD power source from Lincoln Electric and its subsidiary, Uhrhan & Schwill GmbH.

“Thanks to this technology and our unique production process, we believe we are running at least 33 percent faster than any other pipe mill in the world,” says Charlie Lamb, United Spiral Pipe’s vice president of operations.

“If it ain’t broke, don’t fix it” is a pearl of wisdom that apparently has no traction at United Spiral Pipe. Until a year and a half ago, according to Lamb, the company’s production was on par with pipe mills around the world—including a handful in the United States—that manufacture line pipe in a similar fashion.

“Inherently there was no problem with our old tack-weld system using traditional DC-1000 Lincoln Electric power sources that provided large amounts of current to a single GMAW arc, which is the industry standard,” Lamb says, who before joining United Spiral Pipe had been in the industry for three decades. 

Uhrhan & Schwill, committed to providing unique and custom solutions to customers for 50 years, did just that at United Spiral Pipe.  

“Tack welding is a common bottleneck in both longitudinal and spiral pipe mill production all over the world,” says Elmar Schwill, chief engineer at Uhrhan & Schwill. “Working with United Spiral Pipe raised the bar for spiral tacking speeds.” 

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Lincoln Electric’s relationship with United Spiral Pipe has helped push boundaries in many areas of spiral pipe welding. Mark McDowell, Lincoln Electric’s district manager for Northern California and Nevada, has been involved with United Spiral Pipe since the beginning, and continued the partnership with this process innovation.

“From day one, our [Lincoln Electric] team has worked closely with United Spiral Pipe focusing on continual improvement,” he says. “United Spiral Pipe relies on Lincoln Electric to continually bring cutting-edge welding solutions.”

So exactly what is that new setup?

Uhrhan & Schwill integrated a paralleled master-slave configuration of the Power Wave AC/DC 1000 SD using Waveform Control Technology. Lamb says United Spiral Pipe “solely uses various diameters of Lincolnweld L-61 wire, depending on the thickness of the parent material, with a shielding gas mixture of 90/10 CO2/Ar. This, combined with the Power Wave power sources, creates a consistent tack weld with minimal spatter.”

Lincoln Electric’s Waveform Control Technology, with a specific waveform controlling a number of arc parameters for this application, allows welders to create a more consistent tack weld that helps increase welding speeds.

Waveform control, coupled with extremely fast switching speeds of the Power Wave inverter platform, results in arc behavior that is extremely responsive to changes at the workpiece. Great care is taken to control every part of the waveform, corresponding to different parts of the metal droplet transfer. This enables operators to create a more consistent tack weld at increased welding speeds, both at the forming and SAWH stations.

With precise control over metal transfer, operators have the ability to control spatter levels and increase travel speeds, while maintaining proper penetration. This enhances performance consistency from weld to weld.

Quality up, too

Uhrhan & Schwill’s integration of the Power Wave AC/DC 1000 SD system also brings significant quality improvements. Weld quality is confirmed through United Spiral Pipe’s extensive testing processes. Once the spiral pipe leaves the fabrication cycle, it first undergoes hydrostatic testing to an internal pressure of 100 percent of the pipe’s specified minimum yield strength for a minimum of 20 seconds. Next, the entire weld seam is tested using shear wave off-line ultrasonic transducers arranged to pick up longitudinal and transverse defects. Following ultrasonic testing, X-ray testing is performed before the pipe heads to United Spiral Pipe’s coating operations.

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On top of the pipe production world

With production and quality improved, United Spiral Pipe finds itself on top of the world in production speeds for large-diameter pipe for oil and gas. Its willingness to see an opportunity in a situation where it would have been easier to accept the status quo has reaped huge rewards, and positions the company for continued success.

“Any time we are getting increased tonnage out the door, as we are now, that means our bottom-line costs are reduced,” Lamb says. “United Spiral Pipe had great vision to try this new tack-welding technology.” FFJ

David G. Kilburn is the pipe mills global segment director for The Lincoln Electric Co.

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