RIASSUNTO
ABSTRACT
SCRs have been found to have the advantages of relatively low manufacturing cost and good adaptability of floating platform's motion. For deepwater SCRs in extreme harsh environment, a steel lazy-wave riser has been adopted for reducing vessel payload and to decouple vessel motion in touch down zone. However, the challenge in installation and add on cost of buoyancy modules with their uncertain hydrodynamic response have motivated the use of a deep-draft semisubmersible to support conventional SCRs for Lingshui 17-2 field. This paper investigates the design of conventional SCRs to be used in South China Sea.
As the application moves to deepwater and harsh environment, challenges of a conventional SCRs increase significantly in terms of the global performance, fabrication, and installation. This paper starts with SCR properties, coating, VIV suppression device, interface with the pipeline and the semi-submersible platform. This paper further explores the challenges and likely solutions to deepwater SCRs application for Lingshui 17-2 field. One of the challenges is the potential typhoon induced vessel heave motions that may cause significant compression loads at the touchdown zone (TDZ). It may be difficult in designing a SCR to meet working stress-based API RP 2RD requirement thus the newly released API STD 2RD is used to assess riser strength, especially under 1000-yr cyclone environmental conditions.
The SCR design starts with wall thickness sizing for dealing with shut in tubing pressure, flowing temperature, and hang off tension. With the wall thickness sized, the global strength and fatigue assessment of the SCR are investigated to fit for the strength and fatigue requirements. The installation concerns come from the capacity of an installation vessel, and riser pipe size and the water depth. This paper studies the feasibility of S-lay installation for Lingshui 17-2 SCRs. It further investigates the SCR fatigue caused by Vortex-Induced Vibration (VIV) from ambient current. Moreover, Vortex-Induced Motion (VIM) of a semi-submersible platform can adversely affect the result of a SCR fatigue.