CONNECTORS USED IN N. SEA ESV INSTALLATION
Unocal U.K. Ltd., Aberdeen, has recently completed installation of an emergency shutdown valve (ESV) assembly on a North Sea pipeline using connectors rather than welding.
Unocal chose Big-Inch Marine Systems' Flexiforge and ball-flange connectors for inserting the ESV into its Heather Alpha gas-import pipeline in 550 ft of water. This was the first use of mechanical connectors for ESV work in the North Sea. All previous ESV installations have been made with hyperbaric welding, according to Big-Inch.
The installation was completed on contract with Stena Offshore.
Stena divers used the Big Inch cold-forge system to install end connectors on the subsea pipeline on both sides of a new ESV skid. Each forging took 1 hr, with the completion time at 7.5 hr.
The metal-to-metal connection process involves swaging the pipe outward to create a remolded fit into the sleeve part of the connector, making a permanent metal-to-metal seal. This seal is made with an hydraulically powered forging tool which uses tapered planetary rollers driven by a central tapered cone.
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