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.”