Pipeline construction is
divided into three phases, each with its own activities: pre-construction,
construction and post-construction.
Pre-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
prepared, 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.
Construction
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.
Post Construction
Pressure Testing
The pipeline is pressure
tested for a minimum of eight hours using nitrogen, air, water or a mixture of
water and methanol.
Final clean-up
The final step is to reclaim
the pipeline right-of-way and remove any temporary facilities.
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