Pipe Bending Operation to Commence
November 2, 2009
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Over the next few weeks, LOIS contractors will begin towing long sections of pipe to this area for bending. |
With its pipe fusing operation in full swing, the LOIS team is preparing for the next phase in the project which involves bending the fused lengths of High Density Polyethylene (HDPE) pipe into an s-curve for the buoyant, tethered portions of the pipeline. The s-curve design is necessary to allow for temperature fluctuations in the lake.
Since Oswego Lake is a fairly shallow body of water, its temperature can change up to 40 degrees through the seasons. With that kind of change, the pipeline can shrink and grow up to 14 feet over the 2-mile long stretch. The LOIS system design accommodates those temperature fluctuations in three ways: tethers restrain the pipe from bowing up, attached buoyancy pipes restrain the pipe from bowing down, and the s-curve limits side-to-side movement. These measures act in unison to ensure the right grade for gravity flow to the treatment plant.
If the pipe had no s-curve, the pipe could bow to the side, causing the fixed tether to pull the pipe down several feet. That pull would alter the required grade of the pipe. The s-curve limits side-to-side bowing to a fraction of an inch, which allows the system to maintain its seven-foot slope eastward to the wastewater treatment plant.
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The s-curve begins at the buoyant portion of the pipeline. Internodal cables are attached to hold the pipe into the required curve. |
The process of bending 1,200-foot pipe lengths into an s-curve demands a space of at least 300 feet by 1,200 feet on the lake. The work area must also be away from the existing interceptor and away from the areas where piles and anchors have already been installed. With these criteria in mind, an area east of the Lake Grove Swim Park was chosen for pipe bending. A 40-foot by 10-foot barge will mechanically pull the flexible pipe into shape using winches. When the pipe has "relaxed" into the required curve, internodal cables will be attached to the pipe to keep the curve intact. The barge will then move to the opposite side of the pipe and repeat the process until the s-curve is complete for the entire pipe length.
Pipe lengths that will be pile supported won't need bending. After fusing they will be towed to the right location and ‘sunk' into place. These pipe lengths will be installed during the Lake Down phase of the LOIS Project, starting in September 2010.