Optimizing and economizing orbital welding for pipe projects
Although orbital welding technology isn’t new, it continues to evolve, becoming ever more capable and versatile, especially for pipe welds. An interview with Tom Hammer, a journeyman welder at Axenics, Middleton, Mass., reveals some of the many ways this technology can be used to solve difficult welding challenges.
Orbital welding has been around for about 60 years, adding automated functionality to the gas tungsten arc welding process. It’s a reliable, pragmatic approach to performing multiple welds, though some original equipment manufacturers and fabricators have yet to use the power of orbital welding machines, relying on manual welding or other tactics for the joining of metal tube and pipe.
The principles of orbital welding have been in place for decades, but capabilities on new orbital welding machines make them more powerful tools in the welder’s toolkit, as many now feature “smart” functions for easier programming and making quick, refined adjustments before the actual welding begins, ensuring consistent, pure, and reliable weldments.
The team of welders at Axenics, Middleton, Mass., a contract component manufacturer, guides many of its clients toward the practice of orbital welding if the right elements are present for the job.
“When possible, we look to eliminate the human factor in welding, as an orbital welding machine generally results in higher-quality welds,” said Tom Hammer, a journeyman welder at Axenics.
Hi-purity Plumbing Systems for Semiconductor Wafer Production
Although the earliest welding was performed 2,000 years ago, modern welding is an extremely advanced process that is indispensable to other modern technologies and processes. For example, orbital welding can be used to make high-purity plumbing systems for producing semiconductor wafers, which in turn go into essentially everything electronic these days.
One of Axenics’ customers is part of this supply chain. It looked for a contract manufacturer to help expand its production capabilities, specifically creating and installing clean stainless steel pathways for gases to travel through as part of the wafer manufacturing process.
Exceptional cleanness. When producing semiconductors, even a miniscule piece of dust can wreak havoc.
Exceptional welds. Since potentially corrosive gases flow through the system, all welds must have essentially perfect quality to ensure workplace safety and keep the system running smoothly.
Consistent welds. Production for this fabricator was expected to increase by 30%, so it needed a large number of welds. On a small project, a little variation might be acceptable, but as a job grows in scope, consistency from one weld to the next becomes more critical.
Few fittings. A smooth, consistent flow is optimal for most processes and key for semiconductor wafer production. Reducing the number of fittings reduces the number and severity of flow disruptions.
Hammer and the welding team reviewed the customer’s requirements and asked questions, taking cost and time factors into consideration:
- What type of tubing is already being used in the project? Does it need to remain the same?
- What are the size and diameter of the tube being welded?
- How many fittings are needed?
- How much space is required between welds and fittings?
- What kind of finishing is needed?
- Does Axenics have the right head for the orbital welding machine in-house?
- If not, what is the cost to purchase the needed head or produce a custom head for the machine?
The rotating, enclosed orbital welding machines Hammer uses are the Swagelok M200 and Arc Machines model 207A. They can accommodate tube and pipe from 1/16 to 4 in.
“Microheads allow us to get into really tight spots,” he said. “One limitation on orbital welding is whether we have a head that will fit a specific joint. But today you can also wrap chains on pipes to be welded. The welding machine can go over chains, and you’re essentially unlimited on the size of welds you can perform. I’ve seen some setups that perform welds on 20-in. pipe. It’s impressive what these machines can do today.”
Orbital welding is a wise choice for this type of project, taking into consideration the purity requirement, the number of welds needed, and the light wall thickness. For gas flow process control tubing jobs, Hammer often welds on 316L stainless steel.
“That’s when it gets really delicate. We’re talking about welding on paper-thin metal. With manual welding, the slightest adjustment could ruin the weld. That’s why we like to use the orbital weld head, where we can dial in each section of the tube and get it perfect before we put the part in there. We tone the electricity down to a specific amount so we know when we put the part in there, it will be perfect. By hand, the variance is done by eye, and if we step on the pedal too much, it might blow right through the material.”
This job includes hundreds of welds that must be exactly the same. The orbital welding machine used in this job performs one weld in three minutes; Hammer can manually perform a weld on the same piece of stainless steel pipe in about a minute when he’s performing at top speed.
“However, the machine doesn’t slow down. You come in first thing in the morning, and it’s running at max speed, and at the end of the day, it’s still running at max speed,” Hammer said, “I’m at max speed first thing in the morning, but at the end of the day, that’s not the case.”
Keeping contaminants from getting into the stainless steel tubing is essential, which is why high-purity welding for the semiconductor industry is generally performed in a cleanroom, a controlled environment that prevents impurities from entering the weld area.
Hammer uses the same presharpened tungsten in his manual torch that also is used in the orbital machine. While pure argon gas provides external and internal purges in both manual and orbital welding, the welds made by the orbital machines also benefit from taking place in an enclosed space. As the tungsten comes out, the enclosure fills with gas and protects the weld from oxidation. With a hand torch, gas blows on only the side of the tube that is currently being welded.
Generally, orbital welds finish cleaner since gas covers the tube for a longer period of time. Once the weld begins, the argon provides a shield until the welder determines that the weld is cool enough.
Alternative Energy Industry Fabricator
Axenics partners with several alternative energy customers that fabricate hydrogen fuel cells that power a variety of vehicles. For example, some forklifts built for indoor use rely on hydrogen fuel cells to prevent chemical byproducts from damaging edible inventory. The only byproduct of a hydrogen fuel cell is water.
One such customer has many of the same requirements as the semiconductor fabricator, such as weld purity and consistency. It wanted to use 321 stainless steel for thin-wall welds. However, this job was a matter of prototyping a manifold with several valve clusters, each jutting out in different directions, leaving little space for welding.
An orbital welding machine suitable for this job costs around $2,000, and it would be used to fabricate a small number of parts projected to cost the client $250. This wouldn’t make financial sense. However, Hammer has a solution that melds manual and orbital welding techniques.
“In this situation, I would use a spin table,” Hammer said. “It is literally the same action as an orbital welder, but you’re spinning the tube instead of rotating the tungsten electrode around the tube. I use my hand weld torch, but I can clamp my torch into position with a vise to be hands-free, so there’s no wobbling or shaking from a human hand to damage the weld. That cuts out a lot of the factors of human error. It’s not as perfect as an orbital weld, because it’s not in an enclosed environment, but this type of weld can be performed in a cleanroom environment to eliminate contaminants.”
Testing Is Key Even With “Perfect” Orbital Welds
While orbital welding technology offers purity and repeatability, Hammer and his fellow welders know weld integrity is essential to prevent shutdowns caused by weld failures. The company uses nondestructive testing (NDT) on all orbital welds and uses destructive testing on occasion as well.
“Every weld we do gets sight confirmation,” Hammer said. “After that, the weld gets a helium spectrometer test. Some welds get X-ray radiographic testing, depending on the code or customer requirements. Destructive testing is also an option.”
Destructive testing can include a tensile strength test to determine the weld’s ultimate tensile strength. To measure the maximum stress that a weld on material such as 316L stainless steel is able to withstand before failing, the test pulls and stretches the metal to its breaking point.
Welds for alternative energy customers sometimes receive ultrasonic NDT on component weldments for three-pass heat exchanger hydrogen fuel cells used in alternative energy machinery and vehicles.
“It is a key test, since most components we ship will have potentially dangerous gases traveling through them. It’s very important to us and the customer that the stainless steel is flawless with zero leak points,” Hammer said.
Source: The fabricator www.thefabricator.com