Cheyenne Plains Gas Pipeline recently constructed a $425 million natural gas line from Cheyenne, Wyo., to Greensburg, Kan., using 385 miles of X80 steel pipe, a material never before used for pipelines in the United States. Welds on the high-yield steel are prone to hydrogen cracking. The most productive solution for tie-in welds called for a combination of stick and flux-cored wire welding, and that put Miller's PRO 300 CC/CV welding generators in the hands of many pipeline welders for the first time.
Mechanized welding, with inverters, finished the mainline joints, but in 125 miles of the project's first spread, there were 400 manual tie-in welds at river and road crossings. Pipe made from more common steel is traditionally joined with downhill stick welds, but that process would not satisfy all of the concerns about hydrogen cracking.
"Welding uphill with a flux-cored wire was a lot quicker than welding uphill with a low-hydrogen stick electrode, so that's what we selected [for fill and cap passes]," says Sonny Weems, assistant superintendent with Associated Pipe Line, the contractor on Spread 1. Downhill root and hot welds were specified with low-hydrogen stick electrodes.
Older, constant-current (CC) DC generators favored by veteran pipe welders can't deliver the constant-voltage (CV) necessary for wire welding. Associated Pipe Line and welders from Local 798 made practice welds with several wire feeders.
Miller isn't normally the choice of North American pipeline welders, but they chose the PRO 300 for its multi-process capabilities and rented 12 of them to use on the project. The 22-hp CC/CV generator delivers 410 amps of welding output. A single solid-state control board allows it to produce stick, TIG, MIG, and wire welds.
"We had welders put CV boxes (constant-voltage controls) on older DC generators, but they never did perform as well with flux-cored wire," says Weems. "Eventually, we quit using those machines and ran all the procedures with the PRO 300."
Having never used a Miller diesel engine drive, many of the Local 798 welders were hesitant to put them on their trucks. Work on the Cheyenne Plains project changed some attitudes.
"The PRO 300 welded really well — I mean, it has a smooth arc," says welder Junior Blair. He appreciated its four-position Dig control that allowed him to tailor arc force for use with the low-hydrogen stick electrodes. "I could just stick the bead pass in there without turning the heat up or down."
In addition to delivering arc quality necessary for both stick and wire welding, the 22-hp PRO 300 is more efficient than traditional 300-amp welding generators. Miller estimates that it burns 40 percent less fuel.
"I can run the PRO 300 for about four days before I fill up [the 11.5-gallon tank]. If I was running a [competitive machine], I'd need to put in about 10 gallons a day," says Gary Evans, another welder on the project. "We buy our own diesel, so using less fuel makes a big difference."
Miller's PRO 300 has a suggested list price of $9,711.