During construction of our Mariner East and Mariner East 2X pipelines, we have received questions regarding dual-pipeline pullbacks on horizontal directional drill operations where this construction practice is recommended.
Dual-pipeline pullbacks are used to safely install multiple pipelines at once by joining them on a common pulling head and installing them as a bundle. This process has been safely and effectively used for decades in a wide range of infrastructure projects, including water, sewer, energy pipelines and other underground utilities.
Our construction contractors on the Mariner East projects have expert experience with this method, having successfully executed dual-pipeline pullbacks right here in Pennsylvania. They have also used this construction method to safely install infrastructure throughout North America.
The process for installing and pulling back two pipelines using the horizontal directional drilling method is nearly identical to the process for pulling back a single pipe.
- Drill a small-diameter pilot hole along a designed directional path
- Enlarge the pilot hole to a diameter suitable for installation using a reamer
- Skilled and trained pipeliners lay out and weld the pipe sections together
- Pipelines are connected to a swivel head and pulled through the enlarged borehole
Dual-pipeline pullbacks introduce the use of spacers to separate the pipes to prevent metal-to-metal contact. There are no regulations or requirements pertaining to a separation of space between pipelines within the same system.
There are many benefits of installing pipelines using a dual-pipeline pullback construction method. Pipeline operators can safely and efficiently install two pipelines at once, which limits disturbance to the geology by drilling only one borehole at a larger diameter. Additionally, it greatly reduces the construction time by installing two pipelines at once.