Update on the Design of Steel Catenary Riser Systems

SUT, Deep & Ultra Deepwater Offshore Technology
March 1999
S. Hatton

The concept of the steel catenary riser is now well established in the industry. The technology has advanced through numerous studies and JIPs and there are now 4 installations, with more planned in Brazil and Gulf of Mexico in the near future. Steel catenaries are believed by many in the industry to be cost-effective riser solutions that enable deepwater developments. But how mature is the technology? What are the key design issues? How does it compare against competing technologies and what are the future development requirements of the technology?

The steel catenary concept is inherently simple. Lay a pipeline on the seabed and simply pick up the end and connect to the production vessel forming a free hanging ‘simple’ catenary. The beauty of this concept is that it allows the pipeline to be extended to the vessel using standard grade steel, which is cheap. Additionally the riser can be installed using the same lay vessel as the pipeline, saving a dedicated mobilisation.

This arrangement may lead people to the conclusion that deepwater riser systems will in fact be simpler and cheaper than shallow water systems where costly flexible pipe must be considered. However, when steel catenary arrangements are engineered at a detailed level a more complex and costly design emerges. Key issues such as VIV, TDP interaction, thermal insulation/process flow assurance and requirements for weld and inspection quality can cause significant technical complication.

The STRIDE (Steel Risers for Deepwater Environments) JIP was established in 1997 by 2H Offshore Engineering with the objectives of better understanding key issues. The JIP is supported by 20 participants and has been funded to a total of $2.5million. The scope of the JIP covers the following activities:

  • Riser basic sizing and parametric studies
  • Global analysis methods
  • Codes and Standards
  • Installation methods
  • VIV analysis and testing
  • Touch down point analysis methods and testing
  • Material assessment and fabrication requirements

The initial thrust of the JIP was aimed at large diameter risers and extreme environments such as West of Shetland. However, this has now been extended to other environments such as West Africa where there is considerable industry interest.

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