Step 3: Excavating the Trench
The trench for the pipeline is dug after the ROW is cleared of trees. As seen in several of the photos below, the hillsides are so steep that trench diggers are lowered and secured to larger bulldozers with a tether line. If rocks ledges are encountered, track hoes with jack hammers are brought in to create the trench. Sandbags are placed within the trench to restrict water flow and to support the pipe.
Step 4: Pipe Transport, Stringing, & Assembly
When the trench is completed, pre-coated segments of pipe, usually 40 ft in length, are transported from stockpiles in the staging area to the right-of-way. Pipes are laid above ground beside the trench, or within the trench on top of supportive sandbags in steep terrain. Certain pipe sections are bent using a pipe bending tool to allow the pipeline to follow the planned route and the terrain. The pipe sections will then be welded together, sand blasted, and the weld joints coated with epoxy to prevent corrosion. Finally, the weld joints are inspected with x-ray to ensure their quality. Connected lengths of pipe can then be lowered into the trench.
Step 5: Obstacles: Roads & Streams
Pipelines cross existing roads, highways, streams, rivers and wetlands. Typically, pipelines are constructed underneath these obstacles by either boring for shallow depth or using horizontal directional drilling (HDD) for deeper placement. Other obstacles include abandoned mines, karst topography, and densely populated areas. Each obstacles requires a unique method and order of operations.
Step 6: Testing & Restoration
After the pipe is inspected, the trench is filled in. Before completing the project, the pipeline integrity must be verified using hydrostatic testing. Pipeline companies receive permits to withdraw millions of gallons of water from streams and rivers along the pipeline path. This water is sent through the pipeline and the pressure is increased to above the maximum operational level. If the pipeline remains intact during this test, it is deemed operational. After this, the surface of the ROW is seeded and fertilized, and above-ground markers are placed along the pipeline path.