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First S-Lay barge fairing application on Independence Hub riser

13/02/2007

Shell Global Solutions Leads Team to Complete First S-Lay Barge Fairing Application on Independence Hub Riser.

Shell Global Solutions (US) Inc., along with the crew of the Allseas pipelay vessel “Solitaire” and the Independence Hub Integrated Project Team, has achieved the first successful application of fairings during S-Lay operations. The fairings were installed during the laying of a steel catenary riser (SCR) pipeline from the S-Lay vessel in approximately 8,000 feet of water.

“In water this deep, it is prudent for operators to install either helical strakes or fairings to reduce riser vibration induced by vortices caused by ocean current,” said Chris West, project manager for Shell Global Solutions (US) Inc. “It is much more economical to install the vortex induced vibration (VIV) suppression devices during riser installation rather than retrofitting at a later date.”

Historically, helical strake devices have been the only choice for installation during S-Lay operations. In this process, pipe leaves the vessel in an essentially horizontal position and is rolled off a “stinger” (a structure on the back of the ship that curves down into the water and controls the bend radius of the pipe as it transitions to a vertical orientation). Fairings by design rotate freely around the pipe and heretofore have not been able to pass through the v-shaped rollers on the stinger without the possibility of the fairing’s  “tail” being sheared off by the rollers in the stinger.

In the Independence Hub application, polyurethane strakes could not be used on the top portion of the riser because they would provide too much insulation for the gas pipeline. The gas is pressurized at the sea floor and, as it rises and decompresses, it naturally cools and must be heated by the surrounding water to be easily handled at the platform. Engineers determined that helical strakes fastened around the pipeline would insulate the pipe so well that gas would arrive at too cold a temperature for the processing equipment at the platform to handle. So fairings, which allow water to flow around the pipe, were the only option to provide VIV suppression without the unwanted insulation.

Shell Global Solutions developed unique hardware and a rigging procedure that secures the fairing tail in a position away from the stinger rollers of the S-Lay vessel and uses a remotely operated vehicle (ROV) to release the fairing to “weathervane” about the SCR shortly after it enters the water. Fifty-two joints of fairings were successfully installed on the first 10-inch diameter SCR at the Independence Hub, a soon-to-be-installed deep-draft semi-submersible platform in the Mississippi Canyon Block 920 of the Gulf of Mexico. Ten natural gas fields will initially be connected to the platform. Anadarko Petroleum will operate the Independence Hub, which is jointly owned by Enterprise Products Partners L.P. and Helix Energy Solutions, and eight of the initial ten fields.

“Hopefully, operators all over the world will consider this option for their future pipeline projects,” West continued. “Our first job was one of the deepest pipelines in the world, so we know we can handle applications in many more areas.”