Steps of Construction

Step 3: Depositing the Pipeline and Backfilling

Depositing the Pipeline

 

 

Lowering the welded pipe into the trench demands close coordination and skilled operators.

Using a series of side-booms, which are tracked construction equipment, operators simultaneously lift and carefully lower the welded pipe sections into the trench. Non-metallic slings protect the pipe and coating as it is lifted and moved into position.

In rocky areas, a contractor may protect the pipe and coating from damage by placing sandbags or foam blocks at the bottom of the trench on the pipeline prior to placing the pipeline in the trench.

Backfilling

With the pipeline successfully laid in the trench, crews begin backfilling the trench. This can be accomplished with either a backhoe or padding machine depending on the soil type. As with previous construction crews, the backfilling crew takes care to protect the pipeline and coating as the soil is returned to the trench. 

Soil is returned to the trench in reverse order, with the subsoil returned first, followed by the topsoil. This ensures the topsoil goes back to its original position. In areas where the ground is rocky and coarse, crews check the backfill material to remove rocks, bring in clean soil to cover the pipeline, or cover the pipe with a protective material to guard against sharp rocks.

Testing

Before natural gas is transported through a new pipeline, the entire length of the pipeline is pressure tested using water. This hydrostatic testing is one of the final tests to assure safety of the pipeline before it goes into operation.

Requirements for this test are prescribed in DOT’s federal regulations. Each pipeline section is filled with water and pressured up to a level higher than the maximum pressure at which the pipeline will operate when carrying natural gas. 

The test pressure is held for a specific period of time to determine if the pipeline meets the design strength requirements and if any leaks are present. Once a section successfully passes the hydrostatic test, water is safely emptied from the pipeline according to EPA and FERC regulations and the pipeline is dried to ensure that no water is present when natural gas begins to flow.