SCR Life Extension through Managed Shape Change

Event:
OTC
Date:
May 2017
Author:
R. Koska, D. Walters, C. Krapf - 2H, M. Santala, Y. Constantinides - Chevron

Abstract
Steel catenary risers (SCRs) are a cost effective option for deepwater developments. Throughout industry hundreds of SCRs have been deployed and have proven to be highly reliable. Nevertheless, as the inventory of SCRs across industry ages and as operators seek to extend the lives of deepwater platforms beyond their originally intended service life, strategies are needed to ensure that SCRs can continue to operate reliably. Since touchdown point fatigue damage is a strong factor determining the service life of an SCR, strategies to mitigate fatigue damage in this region may be required for service life extension. One such strategy commonly adopted is platform relocation in order to shift the SCR touch down point throughout the life of the field and hence spreading the fatigue damage along the riser touch down region; however, this typically needs to be planned for in the original concept development. In this paper, two additional strategies based on modifying the shape of an existing SCR are presented.

These strategies reduce the fatigue damage rate in the original touchdown point (TDP) region by managing the shape of an existing SCR either through adding buoyancy or by changing the length of the riser such that the original segment of riser pipe in the TDP region is moved to a low stress region. The proposed techniques also accommodate riser response during extreme environmental events. The techniques have been examined based on case studies of a production SCR and an export SCR. Trade-offs in placement of buoyancy and the impact that shape change has on meeting riser strength requirements are presented. It is shown that the potential exists to roughly double the computed fatigue life in the touchdown region.

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