Inverter helps manufacturer achieve improved arc starts, arc control

Situation

Natural gas is a simple compound, CH4, but it’s extremely useful. It has so many household, commercial, and industrial uses that it would be difficult to get by without it.

Extracting it and preparing it for use requires several crucial steps, not least of which is reducing the moisture content. Moisture wreaks havoc on processing equipment, corroding it at moderate temperatures and freezing at low temperatures, so natural gas processors usually use a glycol dehydrator or similar equipment to reduce the moisture content to about 7 pounds per million standard cubic feet.

The drawback is that a dehydrator complicates matters by removing the volatile organic compounds (VOCs) that normally accompany the gas. These VOCs, mainly benzene, toluene, ethylbenzene, and xylene (BTEX), are hazardous and must be disposed of. This is where a purpose-built steam-to-liquid heat exchanger can come in handy. JATCO Inc., Oklahoma City, Okla., manufactures such a device.

JATCO’s equipment, like all of the equipment used in processing fossil fuels, must be robust. The equipment is subject to all manner of worksite stresses and the vagaries of weather, so it has to stand up to quite a bit of abuse. In the case of JATCO’s condenser, it’s a matter of keeping BTEX contained, preventing spills and soil contamination. The company needs good materials and, just as importantly, good welds.

“The condenser is made from ½-in.- OD tubing, 0.035 in. wall thickness, and 5-in.-OD pipe, Schedule 10, welded to the end sheet,” said Steve Correa, general manager. “The Schedule 10 pipe is also welded to a 150-class flange. In other words, it varies from very thin to very thick material, all of which is 304L stainless steel,” he said.

Building one condenser takes quite a bit of effort, about one shift to do all the prep work, fixturing, and welding. The bulk of that effort, of course, is welding.

JATCO had used two other welding machines to build condensers in the past, so the company was familiar with modern welding machine capabilities and had solid expectations when it was shopping around for a new one. Welder Tim Grigsby said that the main issue was plain and simple: The company’s most recently purchased welding machine, a rectifier-based unit, didn’t have very good arc characteristics. He could get the job done, but it was a struggle from the time he struck the arc.

Resolution

After weeks of trials, the company purchased an inverter-based unit, a Heliarc 281i from ESAB. The machine provides AC, pulsed AC, DC, pulsed DC, manual pulsing, and spot welding.

“With this unit, the strikes are smooth, crisp, and consistent,” Grigsby said. “After establishing the arc, it’s smooth sailing. It just runs better,” he said.

Another benefit is that it uses electrical current more efficiently. Grigsby found that he can turn the heat down and obtain just as much penetration as he did with the old machine. Less heat in the weld means less heat in the welder’s workspace, making it a more comfortable environment. It also shaves a bit off JATCO’s monthly electricity bill.

“Another big advantage is the quick-connects for the torch,” Correa said. “This makes changing the torch a breeze.” He also noted that the small footprint makes the unit easy to move around the shop from one workstation to another. “It really helps a growing company like ours,” he said.

Although JATCO has used the unit only on stainless steel so far, its AC settings make it compatible with aluminum. Waveform options such as pulsed AC and pulsed DC, and a control that balances the AC waveform, optimize the arc’s characteristics to suit the specific application.