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API RP 16Q checks for drilling risers

Two preliminary analyses may be performed for a drilling riser:

  • Recommended limits for design and operation: According to the API RP 16Q, a table of inputs and outputs is provided to check the riser stability. For the selected drilling riser model, the minimum slip ring tension and top tension are calculated to ensure the stability of the riser, (so the effective tension is always positive all along the riser). Furthermore, the minimum tension to disconnect the riser with the LMRP is provided. The model would include a tensioner object and a slip joint. The results display in the post-processing window, in the API RP-16Q Check pane, under the Minimum tension tab.

  • Iso-angle curves: According to API RP 16 Q, the top and bottom angle must remain less than maximum allowable angle values. A DeeplinesGUI facility consists in providing envelopes of static iso-angle curves. These curves are displayed in the post-processing window, sheet API RP-16Q Check, in the Iso-angle curves tab.

Warning

The following assumptions are used when computing the minimum tension:

  • Only one mud density is considered along the riser (first line value selected if several lines defined in drilling riser object, tab Mud).
  • Same mud as for main tube used for the auxiliary lines.
  • If included, the TJOB is taken into account.
  • The weight of the riser is derived from the nominal position (no static nor dynamic calculation), and accounts for the buoyancy of submerged parts.

Warning

The analysis is based on a pseudo-analytical calculation with the riser in nominal position (neither static nor dynamic FEM calculation). The range of tension depends on the top tension applied through a tensioner object or directly using an external force. If no tension is defined, the maximum tension would be twice the apparent weight full of mud (same assumption than for Minimum Tension preliminary calculation). The current included in the relevant analysis is used to build the curves, as well as the flexible joints at boundaries.