The American folktale of John Henry tells how this “steel driving man” vowed his sledgehammer and drill bit could bore a dynamite hole faster than any machine. Henry wins the contest, then collapses from the effort. But what if John Henry had taken his heart, muscle and work ethic and applied them to working with the machine? Could he have doubled anyone else's output?
Judging by the most recent collaborative effort of men, machines and welding technology to build a cross-country natural gas pipeline, the answer seems to be a resounding “yes.”
On the first entirely U.S. application of mechanized welding, contractor Murphy Bros., Inc. of East Moline, Ill., and workers from United Association Local 798 Pipeliners Union produced the best-ever American results: an average repair rate of 4.5 percent for the project overall, and a repair rate of 3.0 percent for the last month. Now consider that Murphy Bros. put in an average of 170 joints per day and that the welding power sources had zero downtime.
The project began when Colorado Interstate Gas (CIG, an El Paso Company) ordered a 155-mile loop for its Medicine Bow Lateral. This pipeline will carry natural gas from the Powder River Basin, near Douglas, Wyo., to a mainline just southwest of Cheyenne, Wyo.
Advanced Technology for Speed, Simplicity
The Medicine Bow Lateral Loop provided the opportunity for a combined “technology first” for CRC-Evans Automatic Welding of Houston (mechanized systems) and Miller Electric. This project paired CRC-Evans' P-600 double-headed welding system with distributed control technology with Miller Electric's Invision™ 456MP inverter-based power source with built-in pulsing controls.
“The major benefit of both the P-600 and Invision 456MP is that they simplify the system. Any time you simplify a machine, it becomes more reliable and easier to operate,” says CRC-Evans Vice President Brian Laing. It also becomes faster.
The main gang used seven welding shacks to average 125 joints per day, and 140 joints by the end of the project.
By the end of the project, the main gang averaged 140 joints per day of 36 in. diameter, .531 in. wall pipe,” says Sonny Daniell, a technician for Murphy Bros. on the project. “That's pretty good for 17 welding operators.” Speed was an essential factor on this job, as the entire project, including remediation, had to be completed by November 1 — and it didn't start until June 19.
“We chose mechanized welding because of the time and associated cost constraints,” says Steve Rooney, project supervisor, Murphy Bros. “The customer had supply commitments to keep, and we felt mechanized welding would best achieve the production levels required.”
Because of time constraints “and because we felt it was more efficient, Murphy Bros. went with a main gang and a mini gang,” says Rooney. “The main gang was a bigger crew. We tried to keep the main gang pounding on the real easy welds to improve efficiency and lower the cost per foot. The mini gang was responsible for road and creek crossings, tie-ins, assembling the first few joints of a length and other difficult tasks.” Overall, the main gang on the Medicine Bow Lateral Loop averaged 125 joints per day. The 12-welding operator mini gang averaged 55 joints per day.
Evolution of the Bug
Mechanized welding involves several components, the heart of which is a single- or double-headed welding system, or “bug.” The mechanized bug clamps to a band affixed to the outside diameter of the pipe. Powered by a constant speed, 24-volt DC motor, the bug travels along the band and holds the welding torch(es) in the proper position. The P-600 also features a through-the-arc seam tracker to keep the weld puddle centered in the joint.
“Another advantage of the P-600 is that it provides distributed control,” says Laing. “This means the PC boards controlling the process are physically located on the bug and other system components. With each 'node' providing its own intelligence, we can simplify cabling to a single communication wire between each node.”
CRC-Evans Hardware/Software Engineering Manager, Shankar Rajagopalan, adds that, “This system features the CAN (Control Area Network) communication protocol. Bosch developed CAN for automotive applications, and it has since become an industry standard now that vehicles are computer controlled. The CAN protocol is very robust, so it ensures communication between nodes, and it is very open-ended architecture. This helps us to expand into the digital realm as manufacturers like Miller develop welding power supplies that communicate digitally.”
Baked, Frozen and No Downtime
Though calm now, dusty winds often obscured the next tractor in line. Even in such dusty conditions, the Miller inverters had no downtime.
CRC-Evans selected the Invision 456MP because it is the only power source with built-in controls for pulsed MIG welding. This eliminates the need for pendant-type pulsing controls or programmable wire feeders, eliminates the need for cables between the inverter and pulsing control and improves reliability. “We had zero breakdowns on the Miller inverters,” says Daniell. “Having no downtime at all sure did surprise me, because that's not typical. The other brands of inverters I've used for pulsing had quite a bit of downtime.”
Conditions on the Medicine Bow Lateral put Miller inverters to a rigorous test, too.
“Most days on the early part of the job, the temperatures soared to more than 100 degrees Fahrenheit. Before we were through, it snowed on us several times,” comments Daniell. “The inverters were subjected to plenty of dust, too. Sometimes you couldn't see the tractor in front of you because it was so dusty and windy. For maintenance, I'd take an air compressor and blow out the inverters twice a week, but that was all I ever had to do.”
With America's thirst for natural gas and petroleum, the next large-scale use of mechanized welding is just around the corner. In fact, like the Medicine Bow Lateral Loop, two big lines are set for loops. The Kern River project will stretch from Evanston, Wyo. to Long Beach, Calif., and a second Alaskan Pipeline will run from the North Slope to the lower 48 states. Given their reliability and productivity, there's more than a good chance equipment from Miller Electric and CRC-Evans will be on the job, along with Murphy Bros.
Mechanized Welding Components
1. The tractors. The tractors carry the welding power supplies. For pulsed MIG welding on the three
fill passes, this involves four Invision 456MP inverters and the controllers that link them to the CRC-Evans system. For the short-circuit MIG passes (bead, hot and cap passes), this involves Mille's XMT® 304 inverters.
2. The shack. The tracto's side boom crane hoists a welding shack that fits over the pipeline. The shack prevents wind from affecting the shielding gas and provides a platform for the welding operators and helpers.
3. The central control unit. A cabinet in the shack contains the master controller that runs the entire application. For the P-600 system, this cabinet also contains the wire feeders and their 30-lb. wire spools.
4. Remote control pendant. The P-600 is operated via a remote pendant and can be equipped with CRC-Evans proprietary through-the-arc weld bevel tracking technology. It also features microprocessor control and programmable weld parameters including voltage, current, wire feed speed, travel speed, torch oscillation and shielding gas flow. These features ensure consistent “in spec” welds. The P-600s efficiency allows operators to meet production goals using fewer welding stations as compared to single torch systems. The result is less on-site equipment and a more efficient pipe gang.