Plasma provides pleasant parting process for pipeline project

Situation

Seaway Crude Pipeline Co. LLC, a joint venture that built Seaway pipeline in the mid-1970s, won a contract to build Seaway 2. The second pipeline is much like the first—the pipe is 30 in. dia., ¾ in. thick, and it runs 500 miles, from Cushing, Okla., to Freeport, Texas.

A key difference is that, this time around, the crew, which comprises employees from Enbridge Inc. and Enterprise Products Partners L.P., is using plasma for cuts and repairs rather than oxyfuel. Oxyfuel requires large tanks that can weigh more than 150 lbs. apiece, making them cumbersome to move around on the job site. Also, running out can sometimes mean making a 100-mile round trip to the main staging yard to exchange the empty cylinders for full ones. Meanwhile, an idle crew has to wait until the truck returns.

Resolution

For this project, the crew uses the Freedom PPA, a prototype system from Hypertherm. It consists of a 28-kW, 240-V generator; a built-in air compressor; and the company’s Powermax85 air plasma unit. Capable of cutting 1-in.-thick metal at 20 inches per minute (IPM), the unit has a footprint of 54 by 44 in., allows it to fit onto the small buggies that move along the line.

On the Seaway 2, the unit does a number of tasks, including welder testing and pipe fabrication at the yard, cutting pipe to length and beveling it in the field, and gouging out welds needing repair. In the field, the crews have found that eliminating the use of gas cylinders is just one improvement. Another is cutting speed.

“It’s 100 percent faster,” said Mario Garcia, a welder charged with making engineered cuts to pipe on the line. “With oxyfuel, you’ve got to preheat the pipe, burn the coating back, then make the cut. With [plasma], you just make the cut.”

Cut quality is another factor. The cuts need to be formed with just the right amount of bevel so a welder can come in and properly join the pipe to the line. Dusty Syprett, a welder with about a dozen years of experience on pipelines, said that the process produces smooth, accurate cuts.

Just down the line from Syprett, Ruben Garza is tackling another job common on the pipeline: weld repair. This is perhaps the toughest job for a welder here. Garza has to fix a weld that didn’t pass inspection because it contained a small defect picked up during ultrasonic testing. He needs to remove the old weld and create a new, stronger weld. He worries, though, that he’ll accidentally burn a hole in the pipe. If that happens, the pipe can’t be repaired. A crew will need to come in and replace it completely.

The plasma unit pushes the molten metal out of the groove smoothly, kicking up less molten metal and sending fewer sparks through the air than before. Garza can actually see what he’s doing. “You can see every defect real clearly and keep on gouging until it goes away,” he said. “I have so much more control this way.”

More control means the chances of Garza accidentally melting a hole in the pipe are much lower. Fewer sparks flying through the air results in less risk of a fire breaking out.

Another welder involved in a repair, Levi Rodriquez, also has found that he has more control over the process.

“The best advantage of plasma … is that you can thread a needle with that thing,” he said. “You can take out as little or as much of the weld as you want,” Rodriquez said. “It takes the work right out of the repair. It’s two times faster. It doesn’t throw the fire. There’s no snap. It’s quiet, just a little whistle.”

“I was 12 repairs in the hole when I got here,” he continued. “It took me three days to catch up, and that was with more repairs being added. I was so fast, they had to put another welder behind me. That thing is fast.

Based on this prototype, the manufacturer has developed and released the Freedom 38 PPA. It has more power, 38 kW, and it uses a 125-amp plasma unit. The changes mean workers have the ability to cut slightly thicker pipe, up to 1 in. wall, without sacrificing cut speed or quality.