A pipeline construction project looks much like a moving assembly line. A large project typically is broken into manageable lengths called “spreads,” and utilizes highly specialized and qualified workgroups. Each spread is composed of various crews, each with its own responsibilities. As one crew completes its work, the next crew moves into position to complete its piece of the construction process.
The construction process generally follows the steps outlined as follows:
Before construction begins, crews survey environmental features along proposed pipeline segments. Utility lines and agricultural drainages are located and marked to prevent accidental damage during pipeline construction. Next, the pipeline’s centerline and the exterior right of way boundaries are staked.
Clearing and Grading
The pipeline right of way is cleared of vegetation. Temporary erosion control measures are installed prior to any earth-moving activities.
Topsoil is removed from the work area and stockpiled separately in agricultural areas. Crews use backhoes or trenching machines to excavate a pipeline trench. The soil that is excavated during ditching operations is temporarily stockpiled on the non-working side of the trench.
Individual joints of pipe are strung along the right of way adjacent to the excavated ditch and arranged so they are accessible to construction personnel. A mechanical pipe-bending machine bends individual joints of pipe to the desired angle at locations where there are significant changes in the natural ground contours or where the pipeline route changes direction.
Welding and Coating Pipe
After the stringing and bending are complete, the pipe sections are aligned, welded together, and placed on temporary supports along the edge of the trench. All welds are then visually and radio graphically inspected. Line pipe, normally mill-coated or yard-coated prior to stringing, requires a coating at the welded joints. Prior to the final inspection, the entire pipeline coating is electronically inspected to locate and repair any coating faults or voids.
Lowering Pipe in and Backfilling
The pipe assembly is lowered into the trench by side-boom tractors. The trench is backfilled using a backfilling or bladed equipment; no foreign materials are permitted in the trench.
After backfilling, the pipeline is hydrostatically tested following federal regulations. Test water is obtained and disposed of in accordance with applicable federal, state and local regulations.
Our policy is to clean up and restore the work area as soon as possible. After the pipeline is backfilled and tested, disturbed areas are restored as close as possible to their original contours. Restoration measures are maintained until the area is restored, as closely as possible, to its original condition.
Williams proposes to use a shore to water HDD for the shoreline approach and a water to water HDD crossing of the Ambrose Channel. This technology will enable Williams to avoid sensitive environmental areas near the shoreline while burying the pipe at depths greater than could be achieved with traditional trenching. Williams is proposing a drill under the Ambrose Channel to ensure the pipe is buried at depths to ensure it is adequately protected. From there it will be tied back into the existing Transco offshore pipeline.
In 2016 the company conducted extensive sub-sea survey work in the project area to fully identify the location of environmentally sensitive areas on the ocean floor. Extensive hydrographic & geophysical surveys were conducted using the very latest multi-beam echo sounder, side scan sonar, magnetometer and sub-bottom profiler, technology. As a result, Williams has been able to develop a proposed route that minimizes environmental impacts, including avoiding hard live-bottoms entirely.
Offshore Lay Barge
A lay barge will be used to install the remaining portions of the offshore loop, which would connect to the Rockaway Delivery Lateral one mile offshore form the Rockaway Peninsula.
A lay barge is a complete seagoing plant that allows the pipeline to be assembled and laid continuously along the selected route either on top of the ocean floor or in trenches on the seafloor.
The completed pipeline is lowered into the water by way of the inclined ramp and a stinger attached to the ramp to guide the pipeline to the seafloor at the proper angle. The pipe curves downward from the stern through the water until it reaches the “touchdown point,” or its final position on the seabed. The pipeline is coated with Fusion Bond Epoxy (FBE) coating to prevent external corrosion and a high-density concrete to overcome buoyancy so that it can be sunk into place.
The entire pipeline will be buried in a subsea trench. The pipeline will be lowered below the seabed along its entire length such that the top-of-pipe is a minimum of four feet below the pre-disturbed natural bottom. Upon completion of the pipeline installation, the seabed will be returned to its original contour. The entire offshore construction process is expected to last approximately 12 months.
Horizontal Directional Drill
Williams proposes to use horizontal directional drill (HDD) for two sections of the pipeline route. The first HDD will be a shore approach from Morgan NJ to near offshore. This technology will enable Williams to avoid a major road and rail line in Morgan that traditional trenching would require each to be out of service. The second will be a water-to-water HDD under the Ambrose channel to eliminate additional congestion in the already busy channel.
The project is being designed to have no negative effect on Rockaway or its beaches.
A complete and thorough environmental analysis is being conducted as part of the Federal Energy Regulatory Commission’s review of the project’s certificate application. This application reflects the data collected during extensive sub-sea survey work that has allowed Williams to create a plan to avoid sensitive areas on the ocean floor. Any impacts to the sea floor are largely expected to be temporary in nature.
The company has conducted extensive offshore sediment sampling along the entire project route, in addition to using computer modeling to understand how the pipe burial will affect the sediment movement within the water column. By employing the proposed jet trenching method, nearly all of the sediment would be retained in the trench as the pipeline is lowered. The computer modeling shows that the fraction of the sediment released during jet trenching will remain in the lower half of the water column, such that there would be no visible surface plume. These suspended sediments would settle within the proposed offshore temporary workspace far from the Rockaway Peninsula beaches.