Weight-optimised steel catenary risers and their applications in harsh deepwater environment

In recent years, offshore reservoirs have been developed in deeper and deeper water environments. Steel catenary risers (SCRs) are being considered used in conjunction with a semi-submersible in deepwater and harsh environments such as Northern North Sea, which presents significant design challenges. To increase the understanding of SCR behaviour and improve the design of such systems in deepwater harsh environments, the design modelling framework of deepwater SCR with weight-optimised coating was developed and investigated.The research began by reviewing extensive publications relevant to the understanding of SCRs, limitations in their usage in deepwater and harsh environments had been addressed and establishing a methodology that could effectively unlock the physics and efficiently solve the problem.At a first step, a parametric study on the strength design and analysis for a deepwater SCR with conventional coating, connected to a semi-submersible was carried out to deal with the factors that mainly influence the loading conditions of the riser. However, after every possible regulation of the major design parameters, the dynamic performance of the deepwater SCR with conventional coating was improved but far from meeting the design code requirements.From the outcome configuration with conventional coating, the deepwater SCR was further optimised by weight coating with various distribution plan, thickness and densities. Extreme dynamic analysis showed that the obtained deepwater SCR with weight-optimised coating could satisfy the strength requirements according to the design codes.Following dynamic analysis, fatigue damage verification was executed from nonlinear random time domain analysis results by using specified bilinear S-N curve and rainflow cycle counting. Fatigue analysis results showed that the deepwater SCR with weight-optimised coating can meet the service life requirement. This suggested that weight-optimised coating as a mitigation method for deepwater SCR was effective and adequate for improving its both dynamic and fatigue performance.Investigation was also conducted on the safety of the deepwater SCR with weight- optimised coating. Limit state functions with various models were assessed and compared. A bilinear S-N model based limit state function with wide band correction was found appropriate for fatigue reliability analysis, showing a matching result with fatigue life prediction.A full design procedure for the deepwater SCR with weight-optimised coating, meeting design requirements including strength, fatigue life, and reliability was concluded, which can be applicable for SCRs with various deep water depths. While it is acknowledged that current model may be limited by its semi-empirical basis and issues associated with modelling simulation, it is noted that considerable possibilities for future research and development remains to be explored.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral-pg

Grantor dc:publisher.institution

University of Strathclyde

Year dc:date.issued

2008

Author dc:creator

• Xia, Jie

DOI

10.48730/5f58-mp47

Identifier

uk.bl.ethos.501801
T12251

OAI identifier oai:identifier

oai:strathclyde:5m60qr89m