New Studies Focus on Deepwater SCR Technology

OTC participants learn the latest information on up-and-coming industry solutions during technical sessions.

An integral part of an offshore system - the Steel Catenary Riser (SCR) - was the focus of the first technical session at the Offshore Technology Conference (OTC) in Houston today.

Presenters highlighted various aspects of SCR design, stability and fatigue issues facing the offshore industry. Additionally, another study explored the feasibility of a midwater transfer system that currently is under consideration for an offshore project.

Presenter Roberto Alvim of 2H Offshore said the midwater transfer system he and his co-author P. Elman studied would use a flexible U-shaped riser suspended between an FPSO and a dry tree production platform. "The distance between the vessels is very important to allow for the presence of shuttle vessels," he said. "We recommend a maximum riser length of 1,850 meters." One of the challenges is to make sure the riser never passes below the riser collapse limit. The study also suggested adding a coating to the riser to aid in its buoyancy and installing the riser while it is empty. 

In a paper titled: "Steel Catenary Riser Design Based on Prescribed Motions From Coupled Analysis Methodology," M.V. Rodrigues of Det Norske Veritas suggested that due to a shift to deeper water, more accurate methodologies for SCR design should be based on a coupled analysis rather than the more traditional de-coupled analysis. Under the coupled analysis, all the interactions between the hull, mooring and riser lines are taken into consideration as an integrated dynamic system. "One of the challenges to analysis is the amount of computer time required," he said. "Our study showed the coupled analysis is much more efficient since it uses less computer time." Additionally, the coupled methodology brought better and more realistic results in their study.

Soil conditions were the focus of two different papers: Thomas Langford of the Norwegian Geotechnical Institute presented results from a model test study of SCRs in marine clay while Prof. Charles Aubeny of Texas A&M University studied cyclic tests of model pipe in kaolin.

Stability and fatigue - two highly important issues for SCRs - also received attention from M.K. Hossain of Fugro who did an analysis of subsea umbilical stability while Tom Power of Stress Engineering contrasted the difference between spectral and cycle-counting fatigue damage estimation methods.

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