Taming the Tiger |
January 16, 2012 |
Michels Uses Cradle Bore Machine to Speed Pipeline Project
By Curt Grandia
In the southern United States, where natural resources are abundant and the domestic energy they provide is more and more important to meeting the nation’s demands for fuel, pipeline projects must be fast-tracked and online as quickly as possible to begin paying back the large investment in infrastructure. The $1 billion Tiger Pipeline provides a good example of the speed required on major pipeline projects. Construction began in May 2010 with a firm target service start date of Dec. 1, 2010, so contractors had about six months to install 175 miles of 42-in. natural gas pipeline, stretching from the Carthage, Texas, area to Perryville, La.
The new pipeline’s route followed two existing pipelines for approximately 98 percent of its path. It has a capacity of 2 billion cubic feet per day (Bcf/d), with future committed expansion plans to 2.4 Bcf/d. Ultimately, the Tiger Pipeline will carry natural gas to seven interstate pipelines and one intrastate pipeline supplying natural gas to the Midwest and Northeast.
Working for Energy Transfer Partners, Michels Pipeline Construction, a division of Brownsville, Wis.-based Michels Corp., was one of two contractors on the project to handle under-road bores. The company’s work consisted of approximately 50 bores in northeast Louisiana, beginning at Delhi and continuing west to the Washita River near Monroe. The stretch covered more than 50 miles. Work began in early July and finished in September. To speed its work, Michels’ crews used three McLaughlin CBM 48 cradle boring machines.
“I’ve been around cradle boring machines since I started in the pipeline business, but this is the first time I’ve used a McLaughlin machine,” says Marty Layton, a foreman for Michels. “It takes a lot of power to turn that 42-in. auger, and the McLaughlin cradle bore machines were great on this project. We’ve had cradle rigs and track rigs and different types of boring rigs, but a cradle boring machine in this part of the country is just the fastest, most efficient way to go.”
The McLaughlin CBM 48 cradle boring machine can install steel casings ranging in diameter from 10 to 48 in. and can install casing sections up to 120 ft in one pass.
The cradle boring method helps save pipeline contractors time because it’s not necessary to set up the project as a construction pit, which is often necessary with pit-launched auger boring. Using a track auger boring machine is effective for bores longer than 200 ft and where rock is prevalent. But for shorter bores, like the under-road bores performed by Michels’ crews, cradle boring is ideal. In cradle boring, the crew excavates a trench the length of the casing and the cradle boring machine and casing are suspended in the trench using pipelaying or sideboom equipment. The reduction in setup time helps pipeline contractors complete more bores per day.
“We completed an average bore in one day and that was for a 100-ft bore,” Layton says. “To actually bore, we would pull about 18 in. a minute, so a 90-ft bore would only take about an hour and the rest of the time was spent setting up the site.”
Speed Boring
“The first step in cradle boring is to create the approach to the road crossing by excavating dirt to attain the cover required on the project, which in this case was 5 ft,” Layton says. “The crews used two backhoes to excavate approach areas and attain the required cover.”
At the surface, auger flighting is inserted into each section of a dummy steel casing and the casings are welded together to form a continuous string. A jacking lug, or “dead man,” is installed crossways over the top of the bore pit entrance to provide reaction force for a winch used to pull the assembly forward into the bore.
Then the dummy steel casing is attached to the cradle boring machine by placing the casing string into a cradle on the front of the machine. The auger flighting is attached to the machine and three chains running over the top of the casing secure the string to the cradle boring machine.
The chains are attached to hydraulic cylinders, which provide even pressure on the casing to ensure a secure fit throughout the bore.
Michels had three crews on the project, each of them equipped with a McLaughlin CBM 48 cradle boring machine, two backhoes and two sidebooms. The crews used the backhoes and sidebooms to lower the casing string and cradle boring machine into the trench and help maintain the direction and grade of the bore. A powerful 32.5-ton hydraulic winch pulls the machine forward in the trench as the auger flighting removes spoil.
After sufficient pipe is installed to provide support and maintain line and grade, the casing cradle is removed and only the boring machine is supported. Spoil from the bore is removed by the auger flighting inside the casing back to the machine and deposited into the trench or pit.
Once the casing is installed, the cradle boring machine is disconnected and the auger flighting is pulled back through the installed casing to remove any remaining spoil from the dummy pipe. Then the dummy pipe is extracted and the permanent pipe is installed using the cradle boring machine.
“The McLaughlin machines are getting pretty popular,” Layton says, “especially when installing larger diameter pipe. And that’s because they’re such a strong machine. Completing 50 bores within three months is no easy feat, but the cradle boring machines made that possible.”
Curt Grandia is a features writer for Two Rivers Marketing.