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Catenary Riser System sizing and selection?

asked Oct 9, 2015 in Offshore-Upstream by everetttam (305 points)
What are the typical requirements for a Catenary Riser System in an Offshore Loading System?

4 Answers

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answered Oct 10, 2015 by AngelPenavega (1,025 points)

Select the catenary riser based on the followings:

  • The pipe wall thickness should be selected according to the following criteria:
    1. Maximum internal operating or hydrotest pressures
    2. Collapse due to external hydrostatic pressure during installation or in-service
    3. Local buckling due to the combined effects of external pressure and bending
  • Buckle arrestors should be used in preference to selecting a pipe wall thickness that is sufficient to withstand buckle propagation.
  • Full-scale pipe collapse / buckle propagation testing should be considered in order to confirm the methodologies used in Item b and c above.
  • The Catenary Riser and riser piping should include a minimum corrosion allowance / excess wall thickness of 0.125 in.
  • The wall thickness selected from the above criteria may need to be revised as a result of the strength and fatigue analyses.
  • Standard API line pipe sizes should be used where possible.
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answered Oct 12, 2015 by DeanBidot (360 points)

The Catenary Riser layout should be depended by the subsea pipeline layout and should take into account the following constraints:

  • SCR route should be selected so as to allow riser and flowline installation with regard to the following:
    • Mooring requirements
    • Lay depth
    • Lay curvatures
    • Initiation
    • Termination envelopes
  • Catenary Riser layout should take account of the field mooring systems and the proposed installation method of the Catenary Riser and Floating Facility.
  • Catenary Riser layout should prevent any riser-to-hull, riser-to-riser, or riser-to-mooring line interference for all installation and operational conditions.  If it is found to be impractical to prevent all contact, it should be demonstrated that any limited contact will not be detrimental to the integrity of the riser system or to contacted equipment.
  • Catenary Riser layout should optimize the riser attachment positions for installation considerations and to minimize motion effects.
  • Catenary Riser and pipeline route should provide adequate resistance to prevent slippage of the nominal Catenary Riser touchdown point.
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answered Oct 14, 2015 by AngelPenavega (1,025 points)

Interference analysis should be performed to ensure that the Catenary Riser will not interfere with other risers, mooring lines, or structures.  The potential clashing of the risers that may be caused by vessel motions and riser vortex induced vibration should be analyzed if multiple risers are planned.

The analysis should include effects of Reynold number and uncertainty/inaccuracy in riser tension.  The following contacts should be avoided:

  • Riser to riser
  • Riser to mooring
  • Riser to structure

However, contact may be allowed if it can be demonstrated that the contact condition is rare and the associated forces do not cause any detrimental damage to the riser systems and/or the other components.

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answered Nov 10, 2015 by DeanBidot (360 points)

You should take into account the suppression devices such as helical strakes and fairings that may need to be installed on the riser to suppress vortex-induced vibration (VIV), as determined through a detailed VIV analysis.

The design of the suppression devices should address the following:

  • Installation of the suppression device onto the riser
  • Installation of the riser
  • Maintenance and corrosion protection

The effectiveness of the suppression device should be validated through qualification testing or properly qualified/acceptable prior experience in a similar application.

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