Design of Flexible Risers

R.Chandwani, I.Larsen

Proceedings of the "Workshop on Subsea Pipelines", COPPE/UFRJ-Federal University of Brasil, Rio de Janeiro, Brasil, December 8-9 1997

Flexible pipes, composed of bonded, unbonded or high strength steel or other alloy materials, used as high pressure dynamic risers have increased multifold in the past 20 years or so. Since 1978, when flexible risers were first specified and installed in the Enchova field, offshore Brazil, as part of a floating production system, developments in the design of particularly unbonded and steel risers have made the exploitation of oil/gas resources in deep waters with hostile environments economically viable. Also, in deep waters a compliant topside structure is more economical than a fixed platform. Various designs of compliant topside structural systems such as converted tankers, semi-submersibles with single or multi-point mooring systems with different types of turret and DP systems, tension leg platforms, deep draft platforms, spar platforms, etc., with varying specifications are currently available which comply with the wave motions rather than resist them. Flexible risers are critical components of such floating production systems because they provide the means of transferring the condensate from the seabed to the topside structure and also to exporting the processed fluids from the structure.
In this workshop lecture, some aspects of the design of dynamic flexible risers, unbonded, steel or titanium, are discussed.