It was an historic moment for the underground utility industry.
On Dec. 22, 2004, at approximately 5:25 p.m., the front of a single 3-mi. long pipeline section broke ground in Dare County, NC.
The 6-in. 15,700-ft. long pipeline section, which runs from Point Harbor to Kitty Hawk, was pulled through a hole that was partially drilled and partially excavated under the Currituck Sound. The installation marked a record for length of utility installed with horizontal directional drilling equipment. The pipeline was constructed to provide natural gas service to the Outer Banks of North Carolina in Dare County.
EasternNC Natural Gas Company, a joint venture between the non-profit group Albemarle Pamlico Economic Development Corporation (APEC) and Piedmont, a natural gas distribution company headquartered in Charlotte, NC, began construction in October 2004 on a 6-in. steel natural gas pipeline that will eventually serve customers in the Outer Banks. The existing pipeline that supplies gas to the Outer Banks ended at Point Harbor in Currituck County.
The biggest challenge in completing the extension to the Outer Banks was developing a plan to get the pipeline across the Currituck Sound, a 3-mi. wide body of water.
The Outer Banks is a popular and rapidly growing area, with thousands of vacationers coming every summer to enjoy the beaches. While the contract did not require the work to be done during the off-season, the permit was only valid for a limited time.
In addition, NUCA member Patterson & Wilder Co. Inc., of Wilmington, NC, wanted the minimum traffic possible because they would be working immediately adjacent to Highway 158.
Environmental restrictions required the preservation of seagrasses. Patterson & Wilder initially considered conventional pipe installation, such as excavation, dam and pump, and direct bury of the concrete-coated pipe.
However, after consulting with Michels Directional Crossings, of Brownsville, WI, contractors decided to use horizontal directional drilling technology to install the pipeline under the floor of the Currituck Sound.
Because of the environmental restrictions, it was necessary to drill a minimum of approximately 1,500 ft. on each side of the sound to protect the seagrasses.
“Since we had to drill about 1,500 feet from each side, we decided to go ahead and continue the drills as far as ground conditions would allow in order to further reduce environmental impact,” said Gray Lewis, Patterson & Wilder’s project manager and vice president. “We decided to try to connect the two drill stems together and make one long pull.”
Separate drilling rigs were set up near the Currituck County and Dare County shorelines just south of the Wright Memorial Bridge. Concurrent with drilling operations, Patterson & Wilder crews assembled 15,900 ft. of 6-in. steel pipe in two sections along a temporary work area in Currituck County. The weight of the two sections combined was in excess of 450,000 lbs.
In planning the temporary work space, Patterson & Wilder wanted to avoid setting up the drill string in sections, which would require several welds.
“Every time you stop the drill, there’s the possibility it will seize up down-hole. Then you can’t pull it in any farther, and you can’t pull it out,” Lewis said.
The required 8,000 ft. of continuous temporary workspace was difficult to acquire and the resulting route had many sharp turns and roads to cross. Patterson & Wilder crews had to open-cut three road crossings and install temporary 18-in. sleeves to pull the sections through. By installing these sleeves, traffic flow was maintained. All welds were inspected by QSL Inc., both visually and by x-ray, and the pipe was then pressure-tested to ensure pipeline integrity before the pipe was installed under the sound.
Meanwhile, Michels, the drilling subcontractor for the sound crossing, set up a drill rig on the Outer Banks side that was capable of 1.2 million lbs. of thrust and pullback capacity. Michels then drilled a total distance of 6,727 ft. under Currituck Sound. On the mainland side in Currituck County, Michels set up a drill rig capable of 840,000 lbs. of thrust and pullback capacity. This machine drilled to a maximum distance of 6,144 ft., for a total drilled distance of 12,871 ft. by both rigs. The space between the two drills was then excavated from a barge forming an underwater ditchline that would provide adequate cover for the pipeline. The marine contractor used for this portion of the work was Waff Contracting Inc., of Edenton, NC.
Once the underwater ditch was completed, the two drills then pushed out into the ditch and continued adding drill pipe until reaching one another. When the two drill stems met, they were connected, leaving one continuous length of drill stem in the installation path.
Michels then spent several days preparing the installation path by pulling the drill pipe back toward the Outer Banks side and continuously pumping a natural clay lubricant called bentonite down the drill hole.
“We used nearly 650,000 pounds of bentonite on this project to ensure good movement down-hole,” said Larry Shilman, project manager of Michels.
Another challenge was finding a way to get the product pipe to the point of entry on the mainland side. There were several businesses and a state road that had to be crossed with the pipe string without creating an interruption to traffic flow.
“We decided to use three all-terrain cranes and four shipping containers with rollers placed on them to keep the pipe string elevated enough to provide clearance for traffic. We wanted to minimize the impact to the Point Harbor community,” Lewis said.
Because of the sharp bends in the temporary workspace, Patterson & Wilder took extra time to make sure the pipe would stay on the rollers during the pull. Workers spent a full day pulling the pipeline before the actual pull to see what it was going to do.
“That’s when we learned we were going to have to do things a little differently to get this pipeline to behave — to get it to stay in place,” Lewis said.
Finally, at approximately 4 p.m. on Dec. 20, in the midst of 13-degree temperatures, high winds and snow, the product pipe was attached to the drill stem protruding on the mainland side, and the Outer Banks side rig began to pull. It took approximately 40 workers and 14 pieces of equipment to safely handle the product pipe string during the pull. After more than 49 consecutive hours of effort, the product pipe successfully emerged on the Outer Banks side. The final sound crossing was 15,713 ft.
“This is exciting,” said Lewis. “To our knowledge, nothing of this magnitude has ever been accomplished anywhere else in the world. It was an honor to be a part of a project like this.”
Over the next several weeks, Patterson & Wilder crews continued installing the pipeline along U.S. 158 to a pressure reducing station at the Virginia Dare Welcome Center in Kitty Hawk. This completed the transmission pipeline and allowed the construction of lower pressure distribution lines to provide service to customers to begin along U.S. 158 to Nags Head.
Construction of the distribution lines began in March in Nags Head. Crews from Parker-Stockstill Construction worked their way north to Kitty Hawk up Highway 158 by mid-April.
The first phase of the distribution system serves Kitty Hawk, Kill Devil Hills and Nags Head. The transmission system and the Kitty Hawk Gate station are complete and crews finished purging the transmission line April 25, bringing natural gas to the Outer Banks for the first time ever.
The completed pipeline is part of a project to bring natural gas service to 14 counties of Eastern North Carolina that previously have not had access to natural gas service. The project is being funded by $188.3 million of Natural Gas Infrastructure Bond Funds that were approved by the voters of North Carolina in 1998, and from equity investment by one of EasternNC’s owners, Piedmont Natural Gas Company (Piedmont).
(This article is reprinted, with permission, from the April 2005 issue of “Utility Contractor” magazine, the monthly publication of the National Utility Contractors Association.)
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