20180537 Ver 4_Construction Process - Final_20190827

Page 1 of 4 PIPELINE CONSTRUCTION PROCESS
PIPELINE CONSTRUCTION PROCESS
1. In order to make the right-of-way into a suitable work area, a clearing and grading (reclamation) crew prepares the pipeline corridor so the construction equipment can operate safely.
2. All waterway crossings are flagged prior to clearing to indicate the minimal disturbance zone where equipment and work activities are restricted until the waterway crossing takes place. Access over watercourses is facilitated by using portable bridges installed to span the waterway. For more information, see
WATERWAY CROSSING METHODS on page 4.
3. Next, the mechanical excavation of a trench, dug to a specified depth for pipe placement, is done by the trenching crew. Occasionally, rock drilling and blasting is required to break rock in a controlled manner.
4. After the pipe is delivered to the right-of-way, the contractor "strings" segments of steel pipe by laying the pipe joints on wooden skids adjacent to the trench.
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5. A bending machine is used to tailor the shape of the pipe to conform to the contours of the terrain or to make changes in the direction of the line.
6. The welding crew begins the process of joining the steel pipe into long continuous segments. Welds are then radiographically inspected (X-rayed) to assure pipe joints have been welded in accordance with project specifications.
7. The pipe joints are cleaned and coated and the ditch bottom is cleared of rocks and debris or padded with soft dirt and the pipe is lowered-
in to the ditch by sideboom tractors using belts or cradles in a carefully coordinated action. The ends of the pipe segments are then welded together to form one continuous pipeline.
8. The trench is then backfilled. When soil conditions are not suitable to be directly placed on the pipe, specialized equipment designed to pad the pipe and protect it from sharp rocks and abrasion is utilized.
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9. The newly constructed pipeline must be subjected to pressure testing before it can be placed into service. The purpose of a pressure test is to assure that no defects exist within the pipeline that might threaten its structural integrity. After the test, the pipeline is dried, cleaned and connected to the existing pipeline system.
10. The final phase of the construction is
cleanup and restoration of the right-of-way. This involves replacing topsoil, replanting the right-of way, removing construction material, and restoring the area, as closely as possible, to its original pre-construction condition.
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WATERWAY CROSSING METHODS There are four basic methods for crossing waterways. The crossing method selected for a particular waterway depends on its width and depth, flow rate, environmental sensitivities, adjacent land use and soil conditions. 1.Open-Cut Wet-Ditch MethodThe open-cut wet-ditch method of construction consists of digging an open trench through theundiverted flow of the waterway, laying a prefabricated section of pipe and then backfilling.2.Open-Cut Dry-Ditch MethodThe open-cut dry-ditch method of construction uses sand bags to divert the flow of waterthrough flume pipe(s) that span the construction area to facilitate dry construction conditionsand inhibit water quality impacts.3.Dam & Pump-Around MethodThe pump-around method of construction can act as a substitute to the open-cut dry-ditchmethod of construction for narrow, low-flow streams. In application, small sand bag dams areconstructed both upstream and downstream around the work area across the stream channel.Stream flow is then diverted around the work area using pumps and hoses.4.Horizontal-Directional Drilling (HDD) MethodInstallation of a pipeline by HDD is generally accomplished by drilling a directionallycontrolled hole beneath the waterway and subsequently pulling a pre-fabricated pipe sectionthrough.