Pipeline construction is divided into three phases, each with its own activities: pre-construction, construction and post-construction.
Surveying and staking
Once the pipeline route is finalized crews survey and stake the right-of-way and temporary workspace. Not only will the right-of-way contain the pipeline, it is also where all construction activities occur.
Preparing the right-of-way
The clearly marked right of way is cleared of trees and brush and the top soil is removed and stockpiled for future reclamation. The right-of-way is then leveled and graded to provide access for construction equipment.
Digging the trench
Once the right-of-way is prepare, a trench is dug and the centre line of the trench is surveyed and re-staked. The equipment used to dig the trench varies depending on the type of soil.
Stringing the pipe
Individual lengths of pipe are brought in from stock pile sites and laid out end-to-end along the right-of-way.
Bending and joining the pipe
Individual joints of pipe are bent to fit the terrain using a hydraulic bending machine. Welders join the pipes together using either manual or automated welding technologies. Welding shacks are placed over the joint to prevent the wind from affecting the weld. The welds are then inspected and certified by X-ray or ultrasonic methods.
Coating the pipeline
Coating both inside and outside the pipeline are necessary to prevent it from corroding either from ground water or the product carried in the pipeline. The composition of the internal coating varies with the nature of the product to be transported. The pipes arrive at the construction site pre-coated, however the welded joints must be coated at the site.
Positioning the pipeline
The welded pipeline is lowered into the trench using bulldozers with special cranes called sidebooms.
Installing valves and fittings
Valves and other fittings are installed after the pipeline is in the trench. The valves are used once the line is operational to shut off or isolate part of the pipeline.
Backfilling the trench
Once the pipeline is in place in the trench the topsoil is replaced in the sequence in which it was removed and the land is re-contoured and re-seeded for restoration.
The pipeline is pressure tested for a minimum of eight hours using nitrogen, air, water or a mixture of water and methanol.
The final step is to reclaim the pipeline right-of-way and remove any temporary facilities.
Reference: “Pipeline Construction”. http://www.cepa.com/about-pipelines/pipeline-design-construction/pipeline-construction. January 2014.