STT® Welding Technology – application for pipe welding in shop and outsite

Lincoln Electric’s Patented Surface Tension Transfer® Welding Process Simplifies Six-Month
Industrial Air Separation Plant Process Pipeline Expansion

The job: A major exterior service line expansion at an industrial gas separation plant serving Cleveland’s steel industry. The time frame: Six months. The scope: A labyrinth of exterior piping, ranging in diameter from 6 inches to 30 inches, requiring more than 700 weld joints.

The question: How do you make such a massive project as time-effective and cost-effective as possible?

It’s a daunting task even in the best of conditions, but the welding pros at Ayrshire Inc., a Chardon, Ohio-based industrial and piping contractor, accepted the challenge and succeeded.

For years, pipe fabricators have sought a faster, easier welding method than TIG (GTAW) and stick (SMAW) welding to make single-sided root welds on pipe.  Ayrshire welders have discovered both in the shop and in the field that Surface Tension Transfer® (STT®) is the answer – a gas metal arc welding process used for six months onsite while welding the industrial gas plant’s new external process pipeline.

Since 1978, Ayrshire has responded to the demands of the process, manufacturing, and energy industries.

Lincoln Electric’s patented STT® process eliminates the need for time-consuming TIG and stick welding on pipeline root welds.
The ability to save several different procedure settings in the wire feeder’s digital memory allowed operators to get back to work faster and kept the job moving.

The company understands what it takes to develop durable, quality pipe and seeks the best joining methods to achieve this.  That’s where the company’s conversion to STT® from TIG and stick welding on pipe began.

With a blue-chip client list that includes such companies as the Lubrizol Corp., Millennium Inorganic Chemicals, Ferro Corp., AGA Gas, Kraftmaid, Praxair, Air Products and Duke Energy, Ayrshire strives not only to meet customer expectations for strict quality, but for time-constrained productivity as well. With this in mind, converting to the STT® process on large-scale pipe jobs was a logical step.

“We wanted to use a process that was quicker than old-fashioned stick welding,” says Ayrshire Vice President Ken Jameson. “Wire feeding was an obvious direction for us to take.”

Developed by Lincoln Electric, STT® is a patented, controlled short-circuit transfer GMAW process made possible by the Company’s exclusive Waveform Control Technology®.  The STT® process produces a low hydrogen weld deposit and makes it easier to achieve a high-quality root weld in all positions.

Welders can complete a root pass using STT® and then switch to a different welding process for the fill and cap when using an advanced multi-process welding power source like Lincoln Electric’s Power Wave® 455M/STT®.  The same capabilities are available in the Power Wave® S350 and Power Wave® S500 when paired with an STT® Module.

The Power Wave® welding power sources are high-performance, digitally controlled inverter units designed to be part of a modular, multi-process welding system. Using a compact semiautomatic wire feeder, the STT® process eliminates the need for time-consuming TIG and stick welding on pipeline root welds.

Ayrshire welders quickly learned how efficient this welding process can be – in all kinds of outdoor weather, from 28 degrees F and howling winds to 96 humid degrees F in blazing sun.

“People think of this as an inside welding process because you’re using wire and a shielding gas, but it can be used quite successfully in the field,” says Jim Mikus, of Advanced Gas & Welding Solutions (AGWS) LLC, an independent welding distributor based in Wickliffe, Ohio.

Matt Reuschling, Ayrshire Supervisor (left), Jim Mikus, Advanced Gas (right)

Jim Mikus, Advanced Gas (left), Jason McKee, Ayrshire (right)

Ayrshire first tested the process using this equipment on a large in-shop job in 2009 before taking it into the field in 2010 for the gas plant expansion. Welder Jason McKee says throughout the six months the Ayshire team has been on the job, they have used the STT® process for root welds on all pipe larger than 6 inches in diameter.  The largest diameter pipe the team worked on was 30 inches.

“It’s nothing like stick welding,” McKee says. “It’s easy to pick up and because it’s all digital, you can easily run the settings for the appropriate pipe size and set them in the wire feeder memory for future use.”

Jameson agrees, adding that the digital functionality offers easy setup for each welder.

“Being able to save up to six different welders’ settings saves setup time,” he notes. “If one guy welds at a different wire speed or heat than the guy before him, he simply can push a button and go back to his own settings. It gets him back on the job faster and keeps things moving.”

With a proven quality record, STT® eliminates the lack of penetration and poor sidewall fusion problems commonly encountered when using other, more traditional GMAW power sources.

The STT® process produces a low-hydrogen weld metal deposit in open-root joints with easier operation, better back beads and sidewall fusion, and less spatter and fumes than other processes.

For example, while TIG welding produces good pipe welds, travel speeds are slow, and the heat input required for successful welds is high.

And stick welding with cellulose electrodes provides good fusion characteristics but leaves deep wagon tracks, which requires more labor for grinding. Also common are highly convex root welds and a high-hydrogen deposit which can lead to weld cracking.

In comparison, the STT® process produces a low-hydrogen weld metal deposit in open-root joints with easier operation, better back beads and sidewall fusion, and less spatter and fumes than other processes. It is a viable option for welding in any position and is effective for welding mild and high-strength steels, as well as stainless steel and related alloys.

The original job estimate factored in welding time using TIG root and stick fill and cap for welds on 30-inch pipe at 12 hours for one 30-inch weld.  Using the STT® process onsite, with .045 inch diameter wire and 100% CO2 shielding gas on the root pass and .035 inch diameter wire and a 90% Ar / 10% CO2 shielding gas mix on the fill and cap pass, McKee said he and the welding team could complete two 30 inch, x-ray-quality pipe welds in less than six hours.  The complete project had more than 200 circumferential weld joints on 30 inch pipe and 500 other joints on 6 inch to 24 inch pipe.

“It really does save time,” McKee says. “That’s the biggest benefit.” Another benefit, he shared, is the STT® process capability to easily fill larger gaps on the root pass weld.

“It can fill root gaps up to ¼” to ⅜” inches wide, x-ray quality welds,” he notes. “You couldn’t do that with stick welding. It would be a mess.”

While the STT® equipment is traditionally used in the shop, Jameson knew it would be the perfect solution out in the field.  The Lincoln Electric and AGWS teams worked with him to take a bench model wire feeder designed for stationary use and make it more portable.  Using longer than typical power and control cables (roughly 30 to 50 feet), the wire feeder could be positioned close to the work with a scissor lift while leaving the power source on the ground.

“It makes it a much smaller component and got the job done – on schedule and with quality welds,” Jameson says. “We really credit Lincoln Electric and AGWS for helping us come up with such a workable solution.”

McKee says it was almost effortless for the Ayrshire team to certify on the STT® process thanks to the user-friendly characteristics of STT® and the intensive training program provided by Lincoln and AGWS.

“It only took me about one or two days in the shop to get up to speed before I took and passed the certification test,” he said. “Obviously, welding experience helps, but even guys who had no experience picked it up quickly. While it’s an entirely different machine, it is easier than stick and faster than TIG.  Plus, it’s self-correcting and takes a whole lot of error out of welding. That saves time on the job, too.”

The result:  Ayrshire finished the project on time and on budget and has firmly established itself as the bidder to consider in future pipe welding opportunities.

“The construction industry is a competitive field to say the least, so we’re always looking for an edge” Jameson says. “When we’re putting out bids, if we can say we can finish the job by using the STT® process in one-third of the time that it takes someone using TIG and stick welding, we’ve given ourselves an advantage.  If we can weld a single 30 inch pipe in three to four hours, like we did on this job, and the other guys are doing it in 12 hours, then obviously we can prove we can be the most efficient choice.”