N2K

Safety key as pipelines go under water

Underwater pipeline safety is a key component to pipelines proposed to run to Prince Rupert LNG facilities - TransCanada Pipeline photo
Underwater pipeline safety is a key component to pipelines proposed to run to Prince Rupert LNG facilities
— image credit: TransCanada Pipeline photo

Any pipeline carrying liquefied natural gas from the Northeast to Prince Rupert will make its final approach to the terminal not from the mountains of the coast but from the deep waters of the Pacific Ocean.

It's a process unlike any other seen before on the North Coast; while natural gas flows between the Lower Mainland and Vancouver Island, gas flow in the region stops in Prince Rupert or Kitimat. But laying pipe in the marine environment is nothing new to companies like TransCanada Pipeline, which outlined what is entailed in the process to N2K.

"A contractor with global expertise in laying marine pipelines would use a barge or ship specifically outfitted for marine pipelines. After the pipe segments are welded, they are slowly fed into the water at an angle that avoids overstraining the pipe. The completed pipeline would typically rest on the seabed, but some sections may be buried in a trench to avoid obstruction and to protect the pipe ... the pipe is typically covered in concrete and in some cases may be covered in rock to protect it," explained Davis Sheremata with the TransCanada Corporation.

"The pipeline will rest on the seabed in deep water, up to 600 metres below the surface, or be buried below the seabed ... due to its weight, it will naturally partially bury itself in softer sediments on the seabed so that only a portion of the pipe may remain visible. Where this happens, the pipeline will have no effect on normal fish activity. If harder sediments are encountered the pipeline may not naturally sink into the seabed. Where this is the case and an effect on fish activity is identified, the pipeline can be buried or covered to mitigate the potential effect."

While fish habitat may be impacted during construction, TransCanada notes that the pipeline itself or rock used to protect the pipeline could create new habitat. The company is still determining the best route for the pipeline and is taking into consideration the location of eelgrass beds and other valuable habitat.

Gas flowing through the underwater pipeline would be monitored around the clock at the company's gas control centre, which gathers real-time data on pressure, flow and temperature and would sound a warning of a leak or rupture either on land or under sea. Valves on land at each end of the marine section of pipeline would allow any release to be isolated and stop further flow into the area.

In the event a leak is detected, however, TransCanada said the impact would be almost negligible.

"Natural gas poses few environmental concerns to the ocean in the event of a leak from the pipeline on the seabed. The natural gas will form bubbles and quickly rise to the surface with no direct effect on water quality," explained Sheremata, noting specific emergency response plans are still being developed.

"Natural gas is lighter than air and therefore, on reaching the surface, will disperse into the air and dissipate quickly."

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