A 3 year research program in the U.K. has led to development of equipment to isolate sections of subsea pipelines-equipment said to be useful for installing emergency shutdown valves.
The isolation system uses basic hot tapping and plugging techniques with certain differences.
Comex U.K. Ltd. completed the research program with support from the U.K. Offshore Supplies Office and seven major oil companies.
Because it is not always possible to obtain a perfect seal between the plugging head and the inside pipe wall, the system provides for insertion of a secondary barrier designed to ensure a safe working environment for divers and technicians.
HOW IT WORKS
The secondary barrier, developed by International Testing & Commissioning Ltd., Chesterfield, England, is equipped with spring loaded, retractable drive disks that allow divers to push it into an open ended pipeline with little effort. When the barrier is in place, divers release drive disks and activate the sealing system, using an umbilical to inflate four seals.
The umbilical allows constant monitoring of the secondary barrier, checking its position and sampling the annulus between each seal. A vent between the secondary and primary seals prevents pressure buildup.
The umbilical can be disconnected upon completion of work, allowing the barrier to be pigged out of the line after primary seals have been withdrawn.
In tests at the British Gas Underwater Engineering Facility at Blyth, Northumberland, a 36 in. secondary barrier exceeded its primary design specification, which was to withstand a differential pressure of 29 psi.
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