Riser Design Criteria

  1. Subsea
  2. Production Facilities
  3. Production Engineering


In general, a DNV F2 curve is used for the weld joints and a DNV B curve for the riser connectors (coupling). Two stress concentration factors (SCFs) are used in fatigue analysis, one is 1.2 for the girth welds, and the other is roughly 2.0 for riser connectors, depending on the type of risers. In recent years, fatigue qualification testing has been performed to determine the actual S-N curve data. An engineering criticality assessment (ECA) analysis is conducted to derive defect acceptance criteria for inspection. For the drilling riser, the safety factor on fatigue life is 3 because the drilling joints can be inspected. The fatigue calculations are to account for all relevant load effects, including wave, VIV, and installation-induced fatigue. In some parts, such as the first joints nearest the lower flexjoint (LFJ), the fatigue life could be less, in which case the fatigue life will determine the inspection interval.

Component Capacities

For strength checks, various component capacities need to be defined such as:

  • Wellhead connector;
  • LMRP connector;
  • LFJ;
  • Riser coupling and main pipe;
  • Peripheral lines;
  • Telescopic joint;
  • Tensioner/ring;
  • Active heave draw works;
  • Hard hang-off joint;
  • Soft hang-off joint;
  • Spider-gimbal;
  • Riser running tool.

References

[1] World Oil, Composite Catalog of Oilfield Equipment & Services, forty fifth ed., Gulf Publishing Company, Houston, 2002/03.

[2] International Standards Organization, Petroleum and Natural Gas Industries – Design and Operation of Subsea Production Systems – Part 7: ompletion/Workover/Riser System, ISO 13628-7, 2005.

[3] T. Clausen, R. D’Souza, Dynamic Risers Key Component for Deepwater Drilling, Floating Production, Offshore Magazine, vol. 61, (2001), May.

[4] P.R. Geiger, C.V. Norton, Offshore Vessels, Their Unique and Applications for the Systems Designer, Marine Technology, vol. 32 (No. 1) (1995) 43–76.

[5] American Petroleum Institute, Recommended Practice for Design, Selection, Operation and Maintenance of Marine Drilling Riser Systems, API-RP- 16Q (1993).

[6] American Petroleum Institute, Design of Risers for Floating Production Systems (FPSs) and Tension-Leg Platform (TLPs), API-RP- 2RD (1998).

[7] H. Matlock, Correlations for Design of Laterally Load Piles in Soft Clay, OTC, 2312, Offshore Technology Conference, Houston, Texas, 1975.

[8] K. Vandiver, L. Lee, User Guide for Shear7 Version 4.1, Massachusetts Institute of Technology, Cambridge, 2001, March 25.

[9] J.F. Archard, Contact and Rubbing of Flat Surfaces, Journal of Applied Physics, vol. 24 (No. 8) (1953) 981.


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