Unbonded Flexible Pipe Solutions – An Established Technology for Offshore Nova Scotia & Newfoundland Field Environments

Published: November 2000 | 19^th Offshore Technology Association of Nova Scotia – Petroleum Society Technical Seminar: “New Opportunities – New Challenges” | October 3 – 5, 2000 | Halifax, Nova Scotia, Canada

Abstract

Unbonded flexible pipe solutions are a critical element of floating production systems for the production of oil and gas in offshore field developments. Current applications of flexible pipe solutions encompass high temperatures of up to 130ºC, design pressures as high as 75 MPa, with sour service fluids, for typical internal pipe diameters up to 380 mm (15-inch) for production applications, and even larger in export applications, in water depths as deep as 2000m. Severe environmental conditions; extreme wave and current loads coupled with significant vessel excursions, challenge the design and construction of flexible pipe structures.

In designing a new pipe structure for a riser system application, which is outside the existing envelope of qualification, a full program of prototype testing is usually undertaken to verify the fitness for purpose of the pipe for the intended application. This programme incorporates full scale dynamic tests on prototype pipes, with combined loads of tension, bending and internal pressure. This simulates the vessel loading on the riser during the life of field. The loading conditions for the tests presented are based on floating production systems in the North Sea environment. Examples are given of floating production systems currently in operation in the North Sea to which these rigorous testing regimes were applied.

End fittings are a critical component of the flexible pipe system. They must assure a leak tight transition between subsea and surface facilities, during the applied severe environmental loads and thermal cycling due to start-up and shutdowns, with changes in the fluid barrier material properties over the designed service life. The results of analyses and tests conducted to verify the integrity of the end fitting with thermal cycling and fluid barrier changes due to high temperature production fluids are presented herein.

This paper concludes with a summary of the innovation and qualification programmes that has resulted in Wellstream’s flexible pipe technology been qualified for ultra deep water applications to 2000m, applicable for the future developments of the Scotian Shelf and the Flemish Pass.

Authors:

Tuohy, J., Wang, Dr. D., Baldwin, L.