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ConocoPhillips to safeguard gas lines Twin Tyonek subsea pipelines in Alaska’s Cook Inlet need repairs and protection from erosion; work will involve divers, sand bags Wesley Loy For Petroleum News
ConocoPhillips is preparing to inspect, repair and fortify its twin Tyonek subsea natural gas pipelines in Alaska’s Cook Inlet.
The company laid out its plans in an April 12 packet to regulators in the state Department of Natural Resources.
The 10-inch pipelines connect the Tyonek production platform to a shore-based, 16-inch gas line that feeds the Kenai liquefied natural gas plant.
The inlet is known for its turbulent tides, and erosion has become a threat to the pipelines on the sea floor, ConocoPhillips said.
In fact, the south Tyonek line was “taken out of service last summer due to concerns of the effects of erosion,” the company said.
Eddy effect The Tyonek platform, installed in 1968, produces natural gas from the North Cook Inlet unit.
ConocoPhillips said it plans to work on the subsea gas pipelines between May 1 and Oct. 31.
The work will be performed from boats and involves sending down divers and placing sand bags to protect the lines, the company said.
The initial focus will be the north Tyonek line.
“The purpose of this project is to ensure that the North Tyonek Subsea Pipeline can continue to operate safely by using divers to inspect the pipeline, place sand bags, and make any repairs as needed,” a project description said.
The sand bags will be placed in such a way as to disrupt the “eddy effect” believed to be causing external erosion on exposed areas of the pipelines, ConocoPhillips said.
Time permitting, the company also aims to inspect, repair and sand bag the south Tyonek line.
“These inspections and sand bagging are expected to be a yearly occurrence and will be planned for the life of the field,” the project description added.
Weld joints vulnerable An inspection of the Tyonek pipelines using a tool known as a smart pig found “areas of potential erosion damage on those portions of the pipeline where the pipeline sections are welded together,” the project description said. “Weld joints are not concrete coated, as the rest of the pipeline is, and are covered with a protective synthetic coating. The erosion damage is believed to be caused by an eddy forming between the 2 pipelines.”
On the north pipeline, inspections are planned at 15 locations.
“If external erosion damage is encountered a sleeve will be placed over the area and clamped on to ensure the integrity of the pipeline,” the project description said.
It continued: “At each inspection area, sand bags will be placed around and on top of the weld joints to disrupt the formation of an eddy. Additionally, 124 sand bag locations are planned, which will help prevent further pipeline external erosion of the weld joints on the pipeline. The South Pipeline is often adjacent to the North Pipeline, so when the North Pipeline is sand bagged, the South Pipeline will also be sand bagged in the same area.”
Inspections are planned for 98 locations on the south line, ConocoPhillips said.
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