Pipe Contractor Eliminates Back Purge on Stainless Steel Pipe Welds

Pipe welding root pass change

Increased quality, reduced costs, higher productivity and a motivated workforce: How do you get one without sacrificing another? Pipe fabricator Dixie Mechanical found the answer with a change from traditional methods.

Pipe shops accept an argon back purge as part of the welding process — one that consumes time and drives up costs. Dixie Mechanical was able to eliminate the back purge and generate savings as a result.

With a recent switch in welding processes and a new welding system, the company doubled the number of welds completed every day without compromising quality, allowing them to finish more jobs and meet demanding timelines.

“We’re looking for whatever it takes to make it faster, but we want quality,” says Keith Henline, Dixie Mechanical shop foreman. “At the end of the day, it’s about how much time did you save that operator to make more welds?”

Based in Tuscaloosa, Alabama, Dixie Mechanical fabricates pipe and completes field installation and construction for customers in power and energy, oil and gas, and chemical sectors nationally and internationally. In these critical environments, weld quality is paramount, but fast production and efficiency aren’t far behind.

“Projects are just so much faster nowadays. Being able to meet the customer’s schedule is important, and sometimes the schedules are really demanding,” says Dixie Mechanical President Greg Howell, who founded the company in 2002. “Technology is going to change every day, so you’ve got to keep up with it or you’re going to be behind.”

Welding stainless and carbon steel pipe

With about 75 employees in shop and field operations, Dixie Mechanical typically has four to five projects in the works at any given time. A sizable project for the shop may involve fabricating 2,000 spool pieces; they often produce 300 to 400 feet of pipe daily.

Capabilities include the fabrication of large-bore and small-bore piping, with outer diameters ranging up to 72 inches and wall thickness up to 2-1/4 inches. Commonly welded materials include carbon steel, stainless steel, duplex stainless and chromes. All of the company’s weld procedures and operators are tested and certified to meet ASME Section IX standards.

While weld quality has always been important for Dixie Mechanical, the company wanted to find ways to help save time and produce quality welds more efficiently. Any technology they considered had to demonstrate a good return on investment.

“It’s extremely important that we look at costs every day,” Howell says.

Before: Back purging stainless steel pipe

For welding stainless steel pipe, Dixie Mechanical followed the traditional process of using a TIG root pass with an argon back purge followed by flux-cored fill and cap passes.

The back purge on stainless steel was an especially time-consuming process, typically requiring 20 to 30 minutes depending on the pipe size to set up the argon shielding gas and tape the pipe ends for purging. In addition, the argon gas used for back purging added to consumable costs.

Another productivity killer: Swapping leads and polarities when they changed from TIG welding for the root pass to flux-cored welding for the remaining passes.

“It is just time wasted, really,” Howell says.

After: Eliminating back purge with a multiprocess solution

In looking for efficiency improvements, Dixie Mechanical worked with their local welding supply distributor to test several welding power sources from different manufacturers. They knew it was important to get buy-in from the welders who would use the machines.

“The welders chose the Miller, hands down,” Howell says.

The clear favorite was the PipeWorx 400, a multiprocess system that offers capabilities for MIG, TIG, stick and flux-cored welding as well as the Regulated Metal Deposition (RMD^®) process, a modified short-circuit MIG process from Miller.

With PipeWorx, Dixie Mechanical switched from a TIG root pass to an RMD root pass with high silicon wire from Hobart — allowing them to eliminate the time consuming and costly back purge on stainless steel pipe. RMD uses precisely controlled metal transfer to provide uniform droplet deposition, which makes it easier for the welder to control the weld puddle. Controlled metal transfer and faster puddle freezing mean a less turbulent puddle and that the shielding gas exits the MIG gun relatively undisturbed. This allows the shielding gas to push through the open root, displacing the atmosphere and preventing sugaring or oxidation on the back side of the weld. Such gas coverage is only needed for a short time since the puddle freezes so quickly; eliminating the need for a back purge.

Some customers were initially wary of changing from the traditional TIG process they were familiar with, but the productivity and quality results with RMD helped Dixie Mechanical change minds. The company sends customers coupon samples and test results of welds made with the RMD process that show quality just as high as what is produced with TIG welding.

“It’s just so much faster,” Howell says. “It pays dividends when the welder can stay under that hood. It allows us to do more work.”

Doubling welding productivity

Eliminating the back purge on stainless steel pipe was one major time saver for Dixie Mechanical. Where the back purge could take 20 to 30 minutes per pipe, welders could be set up for the RMD root pass in about five minutes or less.

In addition, the wire-fed RMD process is much more productive than TIG welding, allowing operators to complete more welds in the same amount of time. For an 18-inch pipe, the TIG root pass and back purge followed by flux-cored fill and cap passes often took a few hours. The RMD root pass with no back purge followed by a flux-cored cap pass takes about 30 minutes.

“On average with TIG, I was doing 10 welds, and I can get 20 with RMD. It’s definitely double,” says Joey Sullivan, Dixie Mechanical welder. “The quality is just as good, if not better, and the speed is a lot faster. Pretty impressive.”

Those time and cost savings add up for Dixie Mechanical and help the company compete for jobs and complete work faster.

“We’re gaining more arc time, we’re producing more welds on a shift,” Howell says. “You’re saving time, you’re saving money.”

Producing quality welds

Welding stainless steel presents some unique challenges. The material is often thinner than carbon steel and can’t take as much heat input during welding. The RMD process requires less heat input, helping welders avoid burn-through on the material.

Dixie Mechanical welders also like the consistent flow of the RMD arc. It penetrates well and is more forgiving to changes in welder technique or an inconsistent gap between the parts. Welders can stay in the puddle and go.

“The gap doesn’t have to be exactly the same all the way around, and it will make up for it,” says welder Jeff Hannah. “It’s a lot quicker than the TIG process we used in the past, with just as good of welds.”

Compared to the traditional short arc MIG they had been using for carbon steel pipe, the RMD process doesn’t blow out as much.

Because the RMD process is more forgiving, it helps Dixie Mechanical train new welders and get them on the floor producing quality welds faster.

“We’ve always been proud of our quality,” Howell says. “Our reject rate on testing has always been very low. But I think this makes it easier on the younger guys coming in.”

Easy setup and use

Another factor that makes training easier is the machine’s user-friendly interface. Operators simply push a button to change welding processes. The “plug and play” nature of the system makes it easy for new welders to pick up and use.

It was important for Dixie Mechanical to choose welding systems that made operators of all experience levels feel comfortable.

“After we changed, we saw how easy it was to train everybody on this, even our apprentices,” Henline says. “We can show them how to use it within a few days and before, with the old machines, it would take weeks.”

For all welders, having one machine in the PipeWorx 400 that is capable of every process that Dixie Mechanical uses is a huge benefit. The company outfitted 10 welding cells in its shop with the system, eliminating the need to have two different machines for different welding processes.

“My favorite thing about the PipeWorx is you've got one unit and everything's right there at your fingertips,” Hannah says. “You can switch from TIG to stick to MIG or RMD just by pushing a button. You don’t have to swap everything around.”

Gaining a competitive edge

Investing in PipeWorx 400 welding systems and making the switch to the RMD process has provided Dixie Mechanical with a competitive edge by helping them improve efficiency and reduce costs.

“I think we would be losing out on a lot more opportunities without it. We can produce more with the RMD process against people that aren’t using RMD,” Howell says. “It’s a money saver, no doubt.”

Dixie Mechanical customers have also noticed the efficiencies and faster turnaround times for projects.

“I can’t emphasize enough how fast this process is. We’ve probably doubled the number of welds we make in a day,” Henline says. “We can see growth and our customers notice that it’s a lot faster, too.”

This article first appeared in Welding Journal and is reprinted here with permission from the American Welding Society (AWS).